Auto merge of #100999 - nnethercote:shrink-FnAbi, r=bjorn3

Shrink `FnAbi`

Because they can take up a lot of memory in debug and release builds.

r? `@bjorn3`

35 files changed, 165 insertions, 181 deletions

diff --git a/compiler/rustc_codegen_cranelift/src/abi/comments.rs b/compiler/rustc_codegen_cranelift/src/abi/comments.rs
index 37d2679c10d..7f4619b5c94 100644
--- a/compiler/rustc_codegen_cranelift/src/abi/comments.rs
+++ b/compiler/rustc_codegen_cranelift/src/abi/comments.rs
@@ -24,7 +24,7 @@ pub(super) fn add_arg_comment<'tcx>(
     local: Option<mir::Local>,
     local_field: Option<usize>,
     params: &[Value],
-    arg_abi_mode: PassMode,
+    arg_abi_mode: &PassMode,
     arg_layout: TyAndLayout<'tcx>,
 ) {
     if !fx.clif_comments.enabled() {
diff --git a/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs b/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs
index f4ad76b3bab..96e25d3a8d4 100644
--- a/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs
+++ b/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs
@@ -38,7 +38,7 @@ fn apply_arg_attrs_to_abi_param(mut param: AbiParam, arg_attrs: ArgAttributes) -
     param
 }
 
-fn cast_target_to_abi_params(cast: CastTarget) -> SmallVec<[AbiParam; 2]> {
+fn cast_target_to_abi_params(cast: &CastTarget) -> SmallVec<[AbiParam; 2]> {
     let (rest_count, rem_bytes) = if cast.rest.unit.size.bytes() == 0 {
         (0, 0)
     } else {
@@ -100,7 +100,10 @@ impl<'tcx> ArgAbiExt<'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
                 }
                 _ => unreachable!("{:?}", self.layout.abi),
             },
-            PassMode::Cast(cast) => cast_target_to_abi_params(cast),
+            PassMode::Cast(ref cast, pad_i32) => {
+                assert!(!pad_i32, "padding support not yet implemented");
+                cast_target_to_abi_params(cast)
+            }
             PassMode::Indirect { attrs, extra_attrs: None, on_stack } => {
                 if on_stack {
                     // Abi requires aligning struct size to pointer size
@@ -145,7 +148,9 @@ impl<'tcx> ArgAbiExt<'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
                 }
                 _ => unreachable!("{:?}", self.layout.abi),
             },
-            PassMode::Cast(cast) => (None, cast_target_to_abi_params(cast).into_iter().collect()),
+            PassMode::Cast(ref cast, _) => {
+                (None, cast_target_to_abi_params(cast).into_iter().collect())
+            }
             PassMode::Indirect { attrs: _, extra_attrs: None, on_stack } => {
                 assert!(!on_stack);
                 (Some(AbiParam::special(pointer_ty(tcx), ArgumentPurpose::StructReturn)), vec![])
@@ -160,7 +165,7 @@ impl<'tcx> ArgAbiExt<'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
 pub(super) fn to_casted_value<'tcx>(
     fx: &mut FunctionCx<'_, '_, 'tcx>,
     arg: CValue<'tcx>,
-    cast: CastTarget,
+    cast: &CastTarget,
 ) -> SmallVec<[Value; 2]> {
     let (ptr, meta) = arg.force_stack(fx);
     assert!(meta.is_none());
@@ -179,7 +184,7 @@ pub(super) fn from_casted_value<'tcx>(
     fx: &mut FunctionCx<'_, '_, 'tcx>,
     block_params: &[Value],
     layout: TyAndLayout<'tcx>,
-    cast: CastTarget,
+    cast: &CastTarget,
 ) -> CValue<'tcx> {
     let abi_params = cast_target_to_abi_params(cast);
     let abi_param_size: u32 = abi_params.iter().map(|param| param.value_type.bytes()).sum();
@@ -224,7 +229,7 @@ pub(super) fn adjust_arg_for_abi<'tcx>(
             let (a, b) = arg.load_scalar_pair(fx);
             smallvec![a, b]
         }
-        PassMode::Cast(cast) => to_casted_value(fx, arg, cast),
+        PassMode::Cast(ref cast, _) => to_casted_value(fx, arg, cast),
         PassMode::Indirect { .. } => {
             if is_owned {
                 match arg.force_stack(fx) {
@@ -268,7 +273,7 @@ pub(super) fn cvalue_for_param<'tcx>(
         local,
         local_field,
         &block_params,
-        arg_abi.mode,
+        &arg_abi.mode,
         arg_abi.layout,
     );
 
@@ -282,7 +287,9 @@ pub(super) fn cvalue_for_param<'tcx>(
             assert_eq!(block_params.len(), 2, "{:?}", block_params);
             Some(CValue::by_val_pair(block_params[0], block_params[1], arg_abi.layout))
         }
-        PassMode::Cast(cast) => Some(from_casted_value(fx, &block_params, arg_abi.layout, cast)),
+        PassMode::Cast(ref cast, _) => {
+            Some(from_casted_value(fx, &block_params, arg_abi.layout, cast))
+        }
         PassMode::Indirect { attrs: _, extra_attrs: None, on_stack: _ } => {
             assert_eq!(block_params.len(), 1, "{:?}", block_params);
             Some(CValue::by_ref(Pointer::new(block_params[0]), arg_abi.layout))
diff --git a/compiler/rustc_codegen_cranelift/src/abi/returning.rs b/compiler/rustc_codegen_cranelift/src/abi/returning.rs
index ff3bb2dfd00..aaa1418767a 100644
--- a/compiler/rustc_codegen_cranelift/src/abi/returning.rs
+++ b/compiler/rustc_codegen_cranelift/src/abi/returning.rs
@@ -13,7 +13,7 @@ pub(super) fn codegen_return_param<'tcx>(
     block_params_iter: &mut impl Iterator<Item = Value>,
 ) -> CPlace<'tcx> {
     let (ret_place, ret_param): (_, SmallVec<[_; 2]>) = match fx.fn_abi.as_ref().unwrap().ret.mode {
-        PassMode::Ignore | PassMode::Direct(_) | PassMode::Pair(_, _) | PassMode::Cast(_) => {
+        PassMode::Ignore | PassMode::Direct(_) | PassMode::Pair(_, _) | PassMode::Cast(..) => {
             let is_ssa = ssa_analyzed[RETURN_PLACE] == crate::analyze::SsaKind::Ssa;
             (
                 super::make_local_place(
@@ -44,7 +44,7 @@ pub(super) fn codegen_return_param<'tcx>(
         Some(RETURN_PLACE),
         None,
         &ret_param,
-        fx.fn_abi.as_ref().unwrap().ret.mode,
+        &fx.fn_abi.as_ref().unwrap().ret.mode,
         fx.fn_abi.as_ref().unwrap().ret.layout,
     );
 
@@ -75,7 +75,7 @@ pub(super) fn codegen_with_call_return_arg<'tcx>(
         PassMode::Indirect { attrs: _, extra_attrs: Some(_), on_stack: _ } => {
             unreachable!("unsized return value")
         }
-        PassMode::Direct(_) | PassMode::Pair(_, _) | PassMode::Cast(_) => (None, None),
+        PassMode::Direct(_) | PassMode::Pair(_, _) | PassMode::Cast(..) => (None, None),
     };
 
     let call_inst = f(fx, return_ptr);
@@ -92,7 +92,7 @@ pub(super) fn codegen_with_call_return_arg<'tcx>(
             ret_place
                 .write_cvalue(fx, CValue::by_val_pair(ret_val_a, ret_val_b, ret_arg_abi.layout));
         }
-        PassMode::Cast(cast) => {
+        PassMode::Cast(ref cast, _) => {
             let results =
                 fx.bcx.inst_results(call_inst).iter().copied().collect::<SmallVec<[Value; 2]>>();
             let result =
@@ -131,7 +131,7 @@ pub(crate) fn codegen_return(fx: &mut FunctionCx<'_, '_, '_>) {
             let (ret_val_a, ret_val_b) = place.to_cvalue(fx).load_scalar_pair(fx);
             fx.bcx.ins().return_(&[ret_val_a, ret_val_b]);
         }
-        PassMode::Cast(cast) => {
+        PassMode::Cast(ref cast, _) => {
             let place = fx.get_local_place(RETURN_PLACE);
             let ret_val = place.to_cvalue(fx);
             let ret_vals = super::pass_mode::to_casted_value(fx, ret_val, cast);
diff --git a/compiler/rustc_codegen_gcc/src/abi.rs b/compiler/rustc_codegen_gcc/src/abi.rs
index 0ed3e1fbe93..848c34211ff 100644
--- a/compiler/rustc_codegen_gcc/src/abi.rs
+++ b/compiler/rustc_codegen_gcc/src/abi.rs
@@ -107,45 +107,24 @@ pub trait FnAbiGccExt<'gcc, 'tcx> {
 impl<'gcc, 'tcx> FnAbiGccExt<'gcc, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
     fn gcc_type(&self, cx: &CodegenCx<'gcc, 'tcx>) -> (Type<'gcc>, Vec<Type<'gcc>>, bool, FxHashSet<usize>) {
         let mut on_stack_param_indices = FxHashSet::default();
-        let args_capacity: usize = self.args.iter().map(|arg|
-            if arg.pad.is_some() {
-                1
-            }
-            else {
-                0
-            } +
-            if let PassMode::Pair(_, _) = arg.mode {
-                2
-            } else {
-                1
-            }
-        ).sum();
+
+        // This capacity calculation is approximate.
         let mut argument_tys = Vec::with_capacity(
-            if let PassMode::Indirect { .. } = self.ret.mode {
-                1
-            }
-            else {
-                0
-            } + args_capacity,
+            self.args.len() + if let PassMode::Indirect { .. } = self.ret.mode { 1 } else { 0 }
         );
 
         let return_ty =
             match self.ret.mode {
                 PassMode::Ignore => cx.type_void(),
                 PassMode::Direct(_) | PassMode::Pair(..) => self.ret.layout.immediate_gcc_type(cx),
-                PassMode::Cast(cast) => cast.gcc_type(cx),
+                PassMode::Cast(ref cast, _) => cast.gcc_type(cx),
                 PassMode::Indirect { .. } => {
                     argument_tys.push(cx.type_ptr_to(self.ret.memory_ty(cx)));
                     cx.type_void()
                 }
             };
 
-        for arg in &self.args {
-            // add padding
-            if let Some(ty) = arg.pad {
-                argument_tys.push(ty.gcc_type(cx));
-            }
-
+        for arg in self.args.iter() {
             let arg_ty = match arg.mode {
                 PassMode::Ignore => continue,
                 PassMode::Direct(_) => arg.layout.immediate_gcc_type(cx),
@@ -157,7 +136,13 @@ impl<'gcc, 'tcx> FnAbiGccExt<'gcc, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                 PassMode::Indirect { extra_attrs: Some(_), .. } => {
                     unimplemented!();
                 }
-                PassMode::Cast(cast) => cast.gcc_type(cx),
+                PassMode::Cast(ref cast, pad_i32) => {
+                    // add padding
+                    if pad_i32 {
+                        argument_tys.push(Reg::i32().gcc_type(cx));
+                    }
+                    cast.gcc_type(cx)
+                }
                 PassMode::Indirect { extra_attrs: None, on_stack: true, .. } => {
                     on_stack_param_indices.insert(argument_tys.len());
                     arg.memory_ty(cx)
diff --git a/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs b/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
index 5fbdedac0c4..352fe7568ef 100644
--- a/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
+++ b/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
@@ -130,7 +130,7 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
                 sym::volatile_load | sym::unaligned_volatile_load => {
                     let tp_ty = substs.type_at(0);
                     let mut ptr = args[0].immediate();
-                    if let PassMode::Cast(ty) = fn_abi.ret.mode {
+                    if let PassMode::Cast(ty, _) = &fn_abi.ret.mode {
                         ptr = self.pointercast(ptr, self.type_ptr_to(ty.gcc_type(self)));
                     }
                     let load = self.volatile_load(ptr.get_type(), ptr);
@@ -320,7 +320,7 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
             };
 
         if !fn_abi.ret.is_ignore() {
-            if let PassMode::Cast(ty) = fn_abi.ret.mode {
+            if let PassMode::Cast(ty, _) = &fn_abi.ret.mode {
                 let ptr_llty = self.type_ptr_to(ty.gcc_type(self));
                 let ptr = self.pointercast(result.llval, ptr_llty);
                 self.store(llval, ptr, result.align);
@@ -416,7 +416,7 @@ impl<'gcc, 'tcx> ArgAbiExt<'gcc, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
         else if self.is_unsized_indirect() {
             bug!("unsized `ArgAbi` must be handled through `store_fn_arg`");
         }
-        else if let PassMode::Cast(cast) = self.mode {
+        else if let PassMode::Cast(ref cast, _) = self.mode {
             // FIXME(eddyb): Figure out when the simpler Store is safe, clang
             // uses it for i16 -> {i8, i8}, but not for i24 -> {i8, i8, i8}.
             let can_store_through_cast_ptr = false;
@@ -481,7 +481,7 @@ impl<'gcc, 'tcx> ArgAbiExt<'gcc, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
             PassMode::Indirect { extra_attrs: Some(_), .. } => {
                 OperandValue::Ref(next(), Some(next()), self.layout.align.abi).store(bx, dst);
             },
-            PassMode::Direct(_) | PassMode::Indirect { extra_attrs: None, .. } | PassMode::Cast(_) => {
+            PassMode::Direct(_) | PassMode::Indirect { extra_attrs: None, .. } | PassMode::Cast(..) => {
                 let next_arg = next();
                 self.store(bx, next_arg, dst);
             },
diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs
index 9eb3574e77b..0ce161d7e75 100644
--- a/compiler/rustc_codegen_llvm/src/abi.rs
+++ b/compiler/rustc_codegen_llvm/src/abi.rs
@@ -213,7 +213,7 @@ impl<'ll, 'tcx> ArgAbiExt<'ll, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
             OperandValue::Ref(val, None, self.layout.align.abi).store(bx, dst)
         } else if self.is_unsized_indirect() {
             bug!("unsized `ArgAbi` must be handled through `store_fn_arg`");
-        } else if let PassMode::Cast(cast) = self.mode {
+        } else if let PassMode::Cast(cast, _) = &self.mode {
             // FIXME(eddyb): Figure out when the simpler Store is safe, clang
             // uses it for i16 -> {i8, i8}, but not for i24 -> {i8, i8, i8}.
             let can_store_through_cast_ptr = false;
@@ -283,7 +283,7 @@ impl<'ll, 'tcx> ArgAbiExt<'ll, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
             }
             PassMode::Direct(_)
             | PassMode::Indirect { attrs: _, extra_attrs: None, on_stack: _ }
-            | PassMode::Cast(_) => {
+            | PassMode::Cast(..) => {
                 let next_arg = next();
                 self.store(bx, next_arg, dst);
             }
@@ -325,20 +325,18 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
     fn llvm_type(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type {
         // Ignore "extra" args from the call site for C variadic functions.
         // Only the "fixed" args are part of the LLVM function signature.
-        let args = if self.c_variadic { &self.args[..self.fixed_count] } else { &self.args };
+        let args =
+            if self.c_variadic { &self.args[..self.fixed_count as usize] } else { &self.args };
 
-        let args_capacity: usize = args.iter().map(|arg|
-            if arg.pad.is_some() { 1 } else { 0 } +
-            if let PassMode::Pair(_, _) = arg.mode { 2 } else { 1 }
-        ).sum();
+        // This capacity calculation is approximate.
         let mut llargument_tys = Vec::with_capacity(
-            if let PassMode::Indirect { .. } = self.ret.mode { 1 } else { 0 } + args_capacity,
+            self.args.len() + if let PassMode::Indirect { .. } = self.ret.mode { 1 } else { 0 },
         );
 
-        let llreturn_ty = match self.ret.mode {
+        let llreturn_ty = match &self.ret.mode {
             PassMode::Ignore => cx.type_void(),
             PassMode::Direct(_) | PassMode::Pair(..) => self.ret.layout.immediate_llvm_type(cx),
-            PassMode::Cast(cast) => cast.llvm_type(cx),
+            PassMode::Cast(cast, _) => cast.llvm_type(cx),
             PassMode::Indirect { .. } => {
                 llargument_tys.push(cx.type_ptr_to(self.ret.memory_ty(cx)));
                 cx.type_void()
@@ -346,12 +344,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
         };
 
         for arg in args {
-            // add padding
-            if let Some(ty) = arg.pad {
-                llargument_tys.push(ty.llvm_type(cx));
-            }
-
-            let llarg_ty = match arg.mode {
+            let llarg_ty = match &arg.mode {
                 PassMode::Ignore => continue,
                 PassMode::Direct(_) => arg.layout.immediate_llvm_type(cx),
                 PassMode::Pair(..) => {
@@ -366,7 +359,13 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                     llargument_tys.push(ptr_layout.scalar_pair_element_llvm_type(cx, 1, true));
                     continue;
                 }
-                PassMode::Cast(cast) => cast.llvm_type(cx),
+                PassMode::Cast(cast, pad_i32) => {
+                    // add padding
+                    if *pad_i32 {
+                        llargument_tys.push(Reg::i32().llvm_type(cx));
+                    }
+                    cast.llvm_type(cx)
+                }
                 PassMode::Indirect { attrs: _, extra_attrs: None, on_stack: _ } => {
                     cx.type_ptr_to(arg.memory_ty(cx))
                 }
@@ -426,46 +425,46 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             i += 1;
             i - 1
         };
-        match self.ret.mode {
-            PassMode::Direct(ref attrs) => {
+        match &self.ret.mode {
+            PassMode::Direct(attrs) => {
                 attrs.apply_attrs_to_llfn(llvm::AttributePlace::ReturnValue, cx, llfn);
             }
-            PassMode::Indirect { ref attrs, extra_attrs: _, on_stack } => {
+            PassMode::Indirect { attrs, extra_attrs: _, on_stack } => {
                 assert!(!on_stack);
                 let i = apply(attrs);
                 let sret = llvm::CreateStructRetAttr(cx.llcx, self.ret.layout.llvm_type(cx));
                 attributes::apply_to_llfn(llfn, llvm::AttributePlace::Argument(i), &[sret]);
             }
-            PassMode::Cast(cast) => {
+            PassMode::Cast(cast, _) => {
                 cast.attrs.apply_attrs_to_llfn(llvm::AttributePlace::ReturnValue, cx, llfn);
             }
             _ => {}
         }
-        for arg in &self.args {
-            if arg.pad.is_some() {
-                apply(&ArgAttributes::new());
-            }
-            match arg.mode {
+        for arg in self.args.iter() {
+            match &arg.mode {
                 PassMode::Ignore => {}
-                PassMode::Indirect { ref attrs, extra_attrs: None, on_stack: true } => {
+                PassMode::Indirect { attrs, extra_attrs: None, on_stack: true } => {
                     let i = apply(attrs);
                     let byval = llvm::CreateByValAttr(cx.llcx, arg.layout.llvm_type(cx));
                     attributes::apply_to_llfn(llfn, llvm::AttributePlace::Argument(i), &[byval]);
                 }
-                PassMode::Direct(ref attrs)
-                | PassMode::Indirect { ref attrs, extra_attrs: None, on_stack: false } => {
+                PassMode::Direct(attrs)
+                | PassMode::Indirect { attrs, extra_attrs: None, on_stack: false } => {
                     apply(attrs);
                 }
-                PassMode::Indirect { ref attrs, extra_attrs: Some(ref extra_attrs), on_stack } => {
+                PassMode::Indirect { attrs, extra_attrs: Some(extra_attrs), on_stack } => {
                     assert!(!on_stack);
                     apply(attrs);
                     apply(extra_attrs);
                 }
-                PassMode::Pair(ref a, ref b) => {
+                PassMode::Pair(a, b) => {
                     apply(a);
                     apply(b);
                 }
-                PassMode::Cast(cast) => {
+                PassMode::Cast(cast, pad_i32) => {
+                    if *pad_i32 {
+                        apply(&ArgAttributes::new());
+                    }
                     apply(&cast.attrs);
                 }
             }
@@ -488,17 +487,17 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             i += 1;
             i - 1
         };
-        match self.ret.mode {
-            PassMode::Direct(ref attrs) => {
+        match &self.ret.mode {
+            PassMode::Direct(attrs) => {
                 attrs.apply_attrs_to_callsite(llvm::AttributePlace::ReturnValue, bx.cx, callsite);
             }
-            PassMode::Indirect { ref attrs, extra_attrs: _, on_stack } => {
+            PassMode::Indirect { attrs, extra_attrs: _, on_stack } => {
                 assert!(!on_stack);
                 let i = apply(bx.cx, attrs);
                 let sret = llvm::CreateStructRetAttr(bx.cx.llcx, self.ret.layout.llvm_type(bx));
                 attributes::apply_to_callsite(callsite, llvm::AttributePlace::Argument(i), &[sret]);
             }
-            PassMode::Cast(cast) => {
+            PassMode::Cast(cast, _) => {
                 cast.attrs.apply_attrs_to_callsite(
                     llvm::AttributePlace::ReturnValue,
                     &bx.cx,
@@ -517,13 +516,10 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                 }
             }
         }
-        for arg in &self.args {
-            if arg.pad.is_some() {
-                apply(bx.cx, &ArgAttributes::new());
-            }
-            match arg.mode {
+        for arg in self.args.iter() {
+            match &arg.mode {
                 PassMode::Ignore => {}
-                PassMode::Indirect { ref attrs, extra_attrs: None, on_stack: true } => {
+                PassMode::Indirect { attrs, extra_attrs: None, on_stack: true } => {
                     let i = apply(bx.cx, attrs);
                     let byval = llvm::CreateByValAttr(bx.cx.llcx, arg.layout.llvm_type(bx));
                     attributes::apply_to_callsite(
@@ -532,23 +528,22 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                         &[byval],
                     );
                 }
-                PassMode::Direct(ref attrs)
-                | PassMode::Indirect { ref attrs, extra_attrs: None, on_stack: false } => {
+                PassMode::Direct(attrs)
+                | PassMode::Indirect { attrs, extra_attrs: None, on_stack: false } => {
                     apply(bx.cx, attrs);
                 }
-                PassMode::Indirect {
-                    ref attrs,
-                    extra_attrs: Some(ref extra_attrs),
-                    on_stack: _,
-                } => {
+                PassMode::Indirect { attrs, extra_attrs: Some(extra_attrs), on_stack: _ } => {
                     apply(bx.cx, attrs);
                     apply(bx.cx, extra_attrs);
                 }
-                PassMode::Pair(ref a, ref b) => {
+                PassMode::Pair(a, b) => {
                     apply(bx.cx, a);
                     apply(bx.cx, b);
                 }
-                PassMode::Cast(cast) => {
+                PassMode::Cast(cast, pad_i32) => {
+                    if *pad_i32 {
+                        apply(bx.cx, &ArgAttributes::new());
+                    }
                     apply(bx.cx, &cast.attrs);
                 }
             }
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index 9f364749287..f4227fbd8fa 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -161,7 +161,7 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
             sym::volatile_load | sym::unaligned_volatile_load => {
                 let tp_ty = substs.type_at(0);
                 let ptr = args[0].immediate();
-                let load = if let PassMode::Cast(ty) = fn_abi.ret.mode {
+                let load = if let PassMode::Cast(ty, _) = &fn_abi.ret.mode {
                     let llty = ty.llvm_type(self);
                     let ptr = self.pointercast(ptr, self.type_ptr_to(llty));
                     self.volatile_load(llty, ptr)
@@ -374,7 +374,7 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
         };
 
         if !fn_abi.ret.is_ignore() {
-            if let PassMode::Cast(ty) = fn_abi.ret.mode {
+            if let PassMode::Cast(ty, _) = &fn_abi.ret.mode {
                 let ptr_llty = self.type_ptr_to(ty.llvm_type(self));
                 let ptr = self.pointercast(result.llval, ptr_llty);
                 self.store(llval, ptr, result.align);
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 47a40be5d8c..5c67d3b6431 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -21,7 +21,7 @@ use rustc_middle::ty::{self, Instance, Ty, TypeVisitable};
 use rustc_span::source_map::Span;
 use rustc_span::{sym, Symbol};
 use rustc_symbol_mangling::typeid::typeid_for_fnabi;
-use rustc_target::abi::call::{ArgAbi, FnAbi, PassMode};
+use rustc_target::abi::call::{ArgAbi, FnAbi, PassMode, Reg};
 use rustc_target::abi::{self, HasDataLayout, WrappingRange};
 use rustc_target::spec::abi::Abi;
 
@@ -324,7 +324,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             bx.unreachable();
             return;
         }
-        let llval = match self.fn_abi.ret.mode {
+        let llval = match &self.fn_abi.ret.mode {
             PassMode::Ignore | PassMode::Indirect { .. } => {
                 bx.ret_void();
                 return;
@@ -339,7 +339,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 }
             }
 
-            PassMode::Cast(cast_ty) => {
+            PassMode::Cast(cast_ty, _) => {
                 let op = match self.locals[mir::RETURN_PLACE] {
                     LocalRef::Operand(Some(op)) => op,
                     LocalRef::Operand(None) => bug!("use of return before def"),
@@ -360,7 +360,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         llval
                     }
                 };
-                let ty = bx.cast_backend_type(&cast_ty);
+                let ty = bx.cast_backend_type(cast_ty);
                 let addr = bx.pointercast(llslot, bx.type_ptr_to(ty));
                 bx.load(ty, addr, self.fn_abi.ret.layout.align.abi)
             }
@@ -1158,39 +1158,35 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         llargs: &mut Vec<Bx::Value>,
         arg: &ArgAbi<'tcx, Ty<'tcx>>,
     ) {
-        // Fill padding with undef value, where applicable.
-        if let Some(ty) = arg.pad {
-            llargs.push(bx.const_undef(bx.reg_backend_type(&ty)))
-        }
-
-        if arg.is_ignore() {
-            return;
-        }
-
-        if let PassMode::Pair(..) = arg.mode {
-            match op.val {
+        match arg.mode {
+            PassMode::Ignore => return,
+            PassMode::Cast(_, true) => {
+                // Fill padding with undef value, where applicable.
+                llargs.push(bx.const_undef(bx.reg_backend_type(&Reg::i32())));
+            }
+            PassMode::Pair(..) => match op.val {
                 Pair(a, b) => {
                     llargs.push(a);
                     llargs.push(b);
                     return;
                 }
                 _ => bug!("codegen_argument: {:?} invalid for pair argument", op),
-            }
-        } else if arg.is_unsized_indirect() {
-            match op.val {
+            },
+            PassMode::Indirect { attrs: _, extra_attrs: Some(_), on_stack: _ } => match op.val {
                 Ref(a, Some(b), _) => {
                     llargs.push(a);
                     llargs.push(b);
                     return;
                 }
                 _ => bug!("codegen_argument: {:?} invalid for unsized indirect argument", op),
-            }
+            },
+            _ => {}
         }
 
         // Force by-ref if we have to load through a cast pointer.
         let (mut llval, align, by_ref) = match op.val {
             Immediate(_) | Pair(..) => match arg.mode {
-                PassMode::Indirect { .. } | PassMode::Cast(_) => {
+                PassMode::Indirect { .. } | PassMode::Cast(..) => {
                     let scratch = PlaceRef::alloca(bx, arg.layout);
                     op.val.store(bx, scratch);
                     (scratch.llval, scratch.align, true)
@@ -1222,8 +1218,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
         if by_ref && !arg.is_indirect() {
             // Have to load the argument, maybe while casting it.
-            if let PassMode::Cast(ty) = arg.mode {
-                let llty = bx.cast_backend_type(&ty);
+            if let PassMode::Cast(ty, _) = &arg.mode {
+                let llty = bx.cast_backend_type(ty);
                 let addr = bx.pointercast(llval, bx.type_ptr_to(llty));
                 llval = bx.load(llty, addr, align.min(arg.layout.align.abi));
             } else {
@@ -1622,7 +1618,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             }
             DirectOperand(index) => {
                 // If there is a cast, we have to store and reload.
-                let op = if let PassMode::Cast(_) = ret_abi.mode {
+                let op = if let PassMode::Cast(..) = ret_abi.mode {
                     let tmp = PlaceRef::alloca(bx, ret_abi.layout);
                     tmp.storage_live(bx);
                     bx.store_arg(&ret_abi, llval, tmp);
diff --git a/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs b/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
index 94ac71a4dd2..16aad07194d 100644
--- a/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
@@ -597,8 +597,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         };
 
         if !fn_abi.ret.is_ignore() {
-            if let PassMode::Cast(ty) = fn_abi.ret.mode {
-                let ptr_llty = bx.type_ptr_to(bx.cast_backend_type(&ty));
+            if let PassMode::Cast(ty, _) = &fn_abi.ret.mode {
+                let ptr_llty = bx.type_ptr_to(bx.cast_backend_type(ty));
                 let ptr = bx.pointercast(result.llval, ptr_llty);
                 bx.store(llval, ptr, result.align);
             } else {
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs
index 8ee375fa9e3..c70c2bd9f74 100644
--- a/compiler/rustc_codegen_ssa/src/mir/mod.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/mod.rs
@@ -283,7 +283,7 @@ fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                 for i in 0..tupled_arg_tys.len() {
                     let arg = &fx.fn_abi.args[idx];
                     idx += 1;
-                    if arg.pad.is_some() {
+                    if let PassMode::Cast(_, true) = arg.mode {
                         llarg_idx += 1;
                     }
                     let pr_field = place.project_field(bx, i);
@@ -309,7 +309,7 @@ fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 
             let arg = &fx.fn_abi.args[idx];
             idx += 1;
-            if arg.pad.is_some() {
+            if let PassMode::Cast(_, true) = arg.mode {
                 llarg_idx += 1;
             }
 
diff --git a/compiler/rustc_const_eval/src/interpret/terminator.rs b/compiler/rustc_const_eval/src/interpret/terminator.rs
index f23fa573100..a71a5d4b833 100644
--- a/compiler/rustc_const_eval/src/interpret/terminator.rs
+++ b/compiler/rustc_const_eval/src/interpret/terminator.rs
@@ -214,10 +214,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 _ => false,
             }
         };
-        // Padding must be fully equal.
-        let pad_compat = || caller_abi.pad == callee_abi.pad;
         // When comparing the PassMode, we have to be smart about comparing the attributes.
-        let arg_attr_compat = |a1: ArgAttributes, a2: ArgAttributes| {
+        let arg_attr_compat = |a1: &ArgAttributes, a2: &ArgAttributes| {
             // There's only one regular attribute that matters for the call ABI: InReg.
             // Everything else is things like noalias, dereferencable, nonnull, ...
             // (This also applies to pointee_size, pointee_align.)
@@ -232,13 +230,13 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
             return true;
         };
-        let mode_compat = || match (caller_abi.mode, callee_abi.mode) {
+        let mode_compat = || match (&caller_abi.mode, &callee_abi.mode) {
             (PassMode::Ignore, PassMode::Ignore) => true,
             (PassMode::Direct(a1), PassMode::Direct(a2)) => arg_attr_compat(a1, a2),
             (PassMode::Pair(a1, b1), PassMode::Pair(a2, b2)) => {
                 arg_attr_compat(a1, a2) && arg_attr_compat(b1, b2)
             }
-            (PassMode::Cast(c1), PassMode::Cast(c2)) => c1 == c2,
+            (PassMode::Cast(c1, pad1), PassMode::Cast(c2, pad2)) => c1 == c2 && pad1 == pad2,
             (
                 PassMode::Indirect { attrs: a1, extra_attrs: None, on_stack: s1 },
                 PassMode::Indirect { attrs: a2, extra_attrs: None, on_stack: s2 },
@@ -250,7 +248,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             _ => false,
         };
 
-        if layout_compat() && pad_compat() && mode_compat() {
+        if layout_compat() && mode_compat() {
             return true;
         }
         trace!(
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index 384f17b3cdf..980bb8e8615 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -3251,7 +3251,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
                 .map(|(i, ty)| arg_of(ty, Some(i)))
                 .collect::<Result<_, _>>()?,
             c_variadic: sig.c_variadic,
-            fixed_count: inputs.len(),
+            fixed_count: inputs.len() as u32,
             conv,
             can_unwind: fn_can_unwind(self.tcx(), fn_def_id, sig.abi),
         };
@@ -3323,7 +3323,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
                 }
             };
             fixup(&mut fn_abi.ret);
-            for arg in &mut fn_abi.args {
+            for arg in fn_abi.args.iter_mut() {
                 fixup(arg);
             }
         } else {
diff --git a/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs b/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
index a09b52fbfdf..cb61f76af1d 100644
--- a/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
+++ b/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
@@ -888,7 +888,7 @@ pub fn typeid_for_fnabi<'tcx>(
             typeid.push('v');
         }
     } else {
-        for n in 0..fn_abi.fixed_count {
+        for n in 0..fn_abi.fixed_count as usize {
             let ty = transform_ty(tcx, fn_abi.args[n].layout.ty, transform_ty_options);
             typeid.push_str(&encode_ty(tcx, ty, &mut dict, encode_ty_options));
         }
diff --git a/compiler/rustc_target/src/abi/call/aarch64.rs b/compiler/rustc_target/src/abi/call/aarch64.rs
index 4613a459c51..8a5ad90db71 100644
--- a/compiler/rustc_target/src/abi/call/aarch64.rs
+++ b/compiler/rustc_target/src/abi/call/aarch64.rs
@@ -77,7 +77,7 @@ where
         classify_ret(cx, &mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/amdgpu.rs b/compiler/rustc_target/src/abi/call/amdgpu.rs
index 9be97476ce8..e30dead63cb 100644
--- a/compiler/rustc_target/src/abi/call/amdgpu.rs
+++ b/compiler/rustc_target/src/abi/call/amdgpu.rs
@@ -26,7 +26,7 @@ where
         classify_ret(cx, &mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/arm.rs b/compiler/rustc_target/src/abi/call/arm.rs
index e66c2132b86..1923ea58838 100644
--- a/compiler/rustc_target/src/abi/call/arm.rs
+++ b/compiler/rustc_target/src/abi/call/arm.rs
@@ -88,7 +88,7 @@ where
         classify_ret(cx, &mut fn_abi.ret, vfp);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/avr.rs b/compiler/rustc_target/src/abi/call/avr.rs
index c1f7a1e3af5..e20f01355a4 100644
--- a/compiler/rustc_target/src/abi/call/avr.rs
+++ b/compiler/rustc_target/src/abi/call/avr.rs
@@ -49,7 +49,7 @@ pub fn compute_abi_info<Ty>(fty: &mut FnAbi<'_, Ty>) {
         classify_ret_ty(&mut fty.ret);
     }
 
-    for arg in &mut fty.args {
+    for arg in fty.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/bpf.rs b/compiler/rustc_target/src/abi/call/bpf.rs
index 466c525531c..780e7df4383 100644
--- a/compiler/rustc_target/src/abi/call/bpf.rs
+++ b/compiler/rustc_target/src/abi/call/bpf.rs
@@ -22,7 +22,7 @@ pub fn compute_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
         classify_ret(&mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/hexagon.rs b/compiler/rustc_target/src/abi/call/hexagon.rs
index 8028443b8a6..80a442048d5 100644
--- a/compiler/rustc_target/src/abi/call/hexagon.rs
+++ b/compiler/rustc_target/src/abi/call/hexagon.rs
@@ -21,7 +21,7 @@ pub fn compute_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
         classify_ret(&mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/m68k.rs b/compiler/rustc_target/src/abi/call/m68k.rs
index 58fdc00b696..c1e0f54af5f 100644
--- a/compiler/rustc_target/src/abi/call/m68k.rs
+++ b/compiler/rustc_target/src/abi/call/m68k.rs
@@ -21,7 +21,7 @@ pub fn compute_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
         classify_ret(&mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/mips.rs b/compiler/rustc_target/src/abi/call/mips.rs
index cc443197680..edcd1bab8b4 100644
--- a/compiler/rustc_target/src/abi/call/mips.rs
+++ b/compiler/rustc_target/src/abi/call/mips.rs
@@ -22,10 +22,8 @@ where
     let align = arg.layout.align.max(dl.i32_align).min(dl.i64_align).abi;
 
     if arg.layout.is_aggregate() {
-        arg.cast_to(Uniform { unit: Reg::i32(), total: size });
-        if !offset.is_aligned(align) {
-            arg.pad_with(Reg::i32());
-        }
+        let pad_i32 = !offset.is_aligned(align);
+        arg.cast_to_and_pad_i32(Uniform { unit: Reg::i32(), total: size }, pad_i32);
     } else {
         arg.extend_integer_width_to(32);
     }
@@ -42,7 +40,7 @@ where
         classify_ret(cx, &mut fn_abi.ret, &mut offset);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/mips64.rs b/compiler/rustc_target/src/abi/call/mips64.rs
index cd54167aa7f..2700f67b209 100644
--- a/compiler/rustc_target/src/abi/call/mips64.rs
+++ b/compiler/rustc_target/src/abi/call/mips64.rs
@@ -158,7 +158,7 @@ where
         classify_ret(cx, &mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/mod.rs b/compiler/rustc_target/src/abi/call/mod.rs
index 639ce64a9f5..d2eb804d004 100644
--- a/compiler/rustc_target/src/abi/call/mod.rs
+++ b/compiler/rustc_target/src/abi/call/mod.rs
@@ -26,7 +26,7 @@ mod x86;
 mod x86_64;
 mod x86_win64;
 
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
+#[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)]
 pub enum PassMode {
     /// Ignore the argument.
     ///
@@ -40,9 +40,10 @@ pub enum PassMode {
     ///
     /// The argument has a layout abi of `ScalarPair`.
     Pair(ArgAttributes, ArgAttributes),
-    /// Pass the argument after casting it, to either
-    /// a single uniform or a pair of registers.
-    Cast(CastTarget),
+    /// Pass the argument after casting it, to either a single uniform or a
+    /// pair of registers. The bool indicates if a `Reg::i32()` dummy argument
+    /// is emitted before the real argument.
+    Cast(Box<CastTarget>, bool),
     /// Pass the argument indirectly via a hidden pointer.
     /// The `extra_attrs` value, if any, is for the extra data (vtable or length)
     /// which indicates that it refers to an unsized rvalue.
@@ -463,10 +464,6 @@ impl<'a, Ty> TyAndLayout<'a, Ty> {
 #[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)]
 pub struct ArgAbi<'a, Ty> {
     pub layout: TyAndLayout<'a, Ty>,
-
-    /// Dummy argument, which is emitted before the real argument.
-    pub pad: Option<Reg>,
-
     pub mode: PassMode,
 }
 
@@ -486,7 +483,7 @@ impl<'a, Ty> ArgAbi<'a, Ty> {
             Abi::Vector { .. } => PassMode::Direct(ArgAttributes::new()),
             Abi::Aggregate { .. } => PassMode::Direct(ArgAttributes::new()),
         };
-        ArgAbi { layout, pad: None, mode }
+        ArgAbi { layout, mode }
     }
 
     fn indirect_pass_mode(layout: &TyAndLayout<'a, Ty>) -> PassMode {
@@ -548,11 +545,11 @@ impl<'a, Ty> ArgAbi<'a, Ty> {
     }
 
     pub fn cast_to<T: Into<CastTarget>>(&mut self, target: T) {
-        self.mode = PassMode::Cast(target.into());
+        self.mode = PassMode::Cast(Box::new(target.into()), false);
     }
 
-    pub fn pad_with(&mut self, reg: Reg) {
-        self.pad = Some(reg);
+    pub fn cast_to_and_pad_i32<T: Into<CastTarget>>(&mut self, target: T, pad_i32: bool) {
+        self.mode = PassMode::Cast(Box::new(target.into()), pad_i32);
     }
 
     pub fn is_indirect(&self) -> bool {
@@ -614,7 +611,7 @@ pub enum Conv {
 #[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)]
 pub struct FnAbi<'a, Ty> {
     /// The LLVM types of each argument.
-    pub args: Vec<ArgAbi<'a, Ty>>,
+    pub args: Box<[ArgAbi<'a, Ty>]>,
 
     /// LLVM return type.
     pub ret: ArgAbi<'a, Ty>,
@@ -625,7 +622,7 @@ pub struct FnAbi<'a, Ty> {
     ///
     /// Should only be different from args.len() when c_variadic is true.
     /// This can be used to know whether an argument is variadic or not.
-    pub fixed_count: usize,
+    pub fixed_count: u32,
 
     pub conv: Conv,
 
@@ -730,3 +727,13 @@ impl<'a, Ty> FnAbi<'a, Ty> {
         Ok(())
     }
 }
+
+// Some types are used a lot. Make sure they don't unintentionally get bigger.
+#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
+mod size_asserts {
+    use super::*;
+    use rustc_data_structures::static_assert_size;
+    // These are in alphabetical order, which is easy to maintain.
+    static_assert_size!(ArgAbi<'_, usize>, 56);
+    static_assert_size!(FnAbi<'_, usize>, 80);
+}
diff --git a/compiler/rustc_target/src/abi/call/msp430.rs b/compiler/rustc_target/src/abi/call/msp430.rs
index 0ba73657b5b..33ef47be009 100644
--- a/compiler/rustc_target/src/abi/call/msp430.rs
+++ b/compiler/rustc_target/src/abi/call/msp430.rs
@@ -30,7 +30,7 @@ pub fn compute_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
         classify_ret(&mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/nvptx64.rs b/compiler/rustc_target/src/abi/call/nvptx64.rs
index fc16f1c97a4..4abe51cd697 100644
--- a/compiler/rustc_target/src/abi/call/nvptx64.rs
+++ b/compiler/rustc_target/src/abi/call/nvptx64.rs
@@ -38,7 +38,7 @@ pub fn compute_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
         classify_ret(&mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
@@ -55,7 +55,7 @@ where
         panic!("Kernels should not return anything other than () or !");
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/powerpc.rs b/compiler/rustc_target/src/abi/call/powerpc.rs
index 27a5c6d2fc6..70c32db0a87 100644
--- a/compiler/rustc_target/src/abi/call/powerpc.rs
+++ b/compiler/rustc_target/src/abi/call/powerpc.rs
@@ -21,7 +21,7 @@ pub fn compute_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
         classify_ret(&mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/powerpc64.rs b/compiler/rustc_target/src/abi/call/powerpc64.rs
index c22ef9c8f2a..359bb8fc09a 100644
--- a/compiler/rustc_target/src/abi/call/powerpc64.rs
+++ b/compiler/rustc_target/src/abi/call/powerpc64.rs
@@ -132,7 +132,7 @@ where
         classify_ret(cx, &mut fn_abi.ret, abi);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/riscv.rs b/compiler/rustc_target/src/abi/call/riscv.rs
index 752b44f6434..1cb360f834e 100644
--- a/compiler/rustc_target/src/abi/call/riscv.rs
+++ b/compiler/rustc_target/src/abi/call/riscv.rs
@@ -340,7 +340,7 @@ where
             arg,
             xlen,
             flen,
-            i >= fn_abi.fixed_count,
+            i >= fn_abi.fixed_count as usize,
             &mut avail_gprs,
             &mut avail_fprs,
         );
diff --git a/compiler/rustc_target/src/abi/call/s390x.rs b/compiler/rustc_target/src/abi/call/s390x.rs
index 13706e8c217..ea23692817f 100644
--- a/compiler/rustc_target/src/abi/call/s390x.rs
+++ b/compiler/rustc_target/src/abi/call/s390x.rs
@@ -48,7 +48,7 @@ where
         classify_ret(&mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/sparc.rs b/compiler/rustc_target/src/abi/call/sparc.rs
index cc443197680..edcd1bab8b4 100644
--- a/compiler/rustc_target/src/abi/call/sparc.rs
+++ b/compiler/rustc_target/src/abi/call/sparc.rs
@@ -22,10 +22,8 @@ where
     let align = arg.layout.align.max(dl.i32_align).min(dl.i64_align).abi;
 
     if arg.layout.is_aggregate() {
-        arg.cast_to(Uniform { unit: Reg::i32(), total: size });
-        if !offset.is_aligned(align) {
-            arg.pad_with(Reg::i32());
-        }
+        let pad_i32 = !offset.is_aligned(align);
+        arg.cast_to_and_pad_i32(Uniform { unit: Reg::i32(), total: size }, pad_i32);
     } else {
         arg.extend_integer_width_to(32);
     }
@@ -42,7 +40,7 @@ where
         classify_ret(cx, &mut fn_abi.ret, &mut offset);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/sparc64.rs b/compiler/rustc_target/src/abi/call/sparc64.rs
index cc3a0a69999..1b74959ad17 100644
--- a/compiler/rustc_target/src/abi/call/sparc64.rs
+++ b/compiler/rustc_target/src/abi/call/sparc64.rs
@@ -217,7 +217,7 @@ where
         classify_arg(cx, &mut fn_abi.ret, Size { raw: 32 });
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/wasm.rs b/compiler/rustc_target/src/abi/call/wasm.rs
index 3237cde1065..44427ee5317 100644
--- a/compiler/rustc_target/src/abi/call/wasm.rs
+++ b/compiler/rustc_target/src/abi/call/wasm.rs
@@ -50,7 +50,7 @@ where
         classify_ret(cx, &mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
@@ -66,7 +66,7 @@ pub fn compute_wasm_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
         classify_ret(&mut fn_abi.ret);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/x86.rs b/compiler/rustc_target/src/abi/call/x86.rs
index c7d59baf919..7c26335dcf4 100644
--- a/compiler/rustc_target/src/abi/call/x86.rs
+++ b/compiler/rustc_target/src/abi/call/x86.rs
@@ -49,7 +49,7 @@ where
         }
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
@@ -72,7 +72,7 @@ where
 
         let mut free_regs = 2;
 
-        for arg in &mut fn_abi.args {
+        for arg in fn_abi.args.iter_mut() {
             let attrs = match arg.mode {
                 PassMode::Ignore
                 | PassMode::Indirect { attrs: _, extra_attrs: None, on_stack: _ } => {
@@ -81,7 +81,7 @@ where
                 PassMode::Direct(ref mut attrs) => attrs,
                 PassMode::Pair(..)
                 | PassMode::Indirect { attrs: _, extra_attrs: Some(_), on_stack: _ }
-                | PassMode::Cast(_) => {
+                | PassMode::Cast(..) => {
                     unreachable!("x86 shouldn't be passing arguments by {:?}", arg.mode)
                 }
             };
diff --git a/compiler/rustc_target/src/abi/call/x86_64.rs b/compiler/rustc_target/src/abi/call/x86_64.rs
index a52e01a495a..c0c071a614f 100644
--- a/compiler/rustc_target/src/abi/call/x86_64.rs
+++ b/compiler/rustc_target/src/abi/call/x86_64.rs
@@ -239,7 +239,7 @@ where
         x86_64_arg_or_ret(&mut fn_abi.ret, false);
     }
 
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }
diff --git a/compiler/rustc_target/src/abi/call/x86_win64.rs b/compiler/rustc_target/src/abi/call/x86_win64.rs
index 2aad641b1ec..1aaf0e511ca 100644
--- a/compiler/rustc_target/src/abi/call/x86_win64.rs
+++ b/compiler/rustc_target/src/abi/call/x86_win64.rs
@@ -31,7 +31,7 @@ pub fn compute_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
     if !fn_abi.ret.is_ignore() {
         fixup(&mut fn_abi.ret);
     }
-    for arg in &mut fn_abi.args {
+    for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }