Move `ArgAbi::pad_i32` into `PassMode::Cast`.

Because it's only needed for that variant. This shrinks the types and
clarifies the logic.

14 files changed, 80 insertions, 88 deletions

diff --git a/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs b/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs
index 058dee176e2..165f15bb3f1 100644
--- a/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs
+++ b/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs
@@ -100,7 +100,10 @@ impl<'tcx> ArgAbiExt<'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
                 }
                 _ => unreachable!("{:?}", self.layout.abi),
             },
-            PassMode::Cast(ref 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 +148,7 @@ impl<'tcx> ArgAbiExt<'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
                 }
                 _ => unreachable!("{:?}", self.layout.abi),
             },
-            PassMode::Cast(ref cast) => {
+            PassMode::Cast(ref cast, _) => {
                 (None, cast_target_to_abi_params(cast).into_iter().collect())
             }
             PassMode::Indirect { attrs: _, extra_attrs: None, on_stack } => {
@@ -226,7 +229,7 @@ pub(super) fn adjust_arg_for_abi<'tcx>(
             let (a, b) = arg.load_scalar_pair(fx);
             smallvec![a, b]
         }
-        PassMode::Cast(ref 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) {
@@ -284,7 +287,7 @@ 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(ref cast) => {
+        PassMode::Cast(ref cast, _) => {
             Some(from_casted_value(fx, &block_params, arg_abi.layout, cast))
         }
         PassMode::Indirect { attrs: _, extra_attrs: None, on_stack: _ } => {
diff --git a/compiler/rustc_codegen_cranelift/src/abi/returning.rs b/compiler/rustc_codegen_cranelift/src/abi/returning.rs
index 29ef5e2dfda..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(
@@ -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(ref 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(ref 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 3186b363e35..848c34211ff 100644
--- a/compiler/rustc_codegen_gcc/src/abi.rs
+++ b/compiler/rustc_codegen_gcc/src/abi.rs
@@ -117,7 +117,7 @@ impl<'gcc, 'tcx> FnAbiGccExt<'gcc, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             match self.ret.mode {
                 PassMode::Ignore => cx.type_void(),
                 PassMode::Direct(_) | PassMode::Pair(..) => self.ret.layout.immediate_gcc_type(cx),
-                PassMode::Cast(ref 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()
@@ -125,11 +125,6 @@ impl<'gcc, 'tcx> FnAbiGccExt<'gcc, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             };
 
         for arg in self.args.iter() {
-            // add padding
-            if arg.pad_i32 {
-                argument_tys.push(Reg::i32().gcc_type(cx));
-            }
-
             let arg_ty = match arg.mode {
                 PassMode::Ignore => continue,
                 PassMode::Direct(_) => arg.layout.immediate_gcc_type(cx),
@@ -141,7 +136,13 @@ impl<'gcc, 'tcx> FnAbiGccExt<'gcc, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                 PassMode::Indirect { extra_attrs: Some(_), .. } => {
                     unimplemented!();
                 }
-                PassMode::Cast(ref 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 f4493776ea2..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(ref 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 168cf3d0b58..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);
             }
@@ -336,7 +336,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
         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()
@@ -344,11 +344,6 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
         };
 
         for arg in args {
-            // add padding
-            if arg.pad_i32 {
-                llargument_tys.push(Reg::i32().llvm_type(cx));
-            }
-
             let llarg_ty = match &arg.mode {
                 PassMode::Ignore => continue,
                 PassMode::Direct(_) => arg.layout.immediate_llvm_type(cx),
@@ -364,7 +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))
                 }
@@ -434,15 +435,12 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                 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.iter() {
-            if arg.pad_i32 {
-                apply(&ArgAttributes::new());
-            }
             match &arg.mode {
                 PassMode::Ignore => {}
                 PassMode::Indirect { attrs, extra_attrs: None, on_stack: true } => {
@@ -463,7 +461,10 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                     apply(a);
                     apply(b);
                 }
-                PassMode::Cast(cast) => {
+                PassMode::Cast(cast, pad_i32) => {
+                    if *pad_i32 {
+                        apply(&ArgAttributes::new());
+                    }
                     apply(&cast.attrs);
                 }
             }
@@ -496,7 +497,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                 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,
@@ -516,9 +517,6 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             }
         }
         for arg in self.args.iter() {
-            if arg.pad_i32 {
-                apply(bx.cx, &ArgAttributes::new());
-            }
             match &arg.mode {
                 PassMode::Ignore => {}
                 PassMode::Indirect { attrs, extra_attrs: None, on_stack: true } => {
@@ -542,7 +540,10 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                     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 d46a6dd32c8..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 5b3f41263e7..5c67d3b6431 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -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"),
@@ -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 arg.pad_i32 {
-            llargs.push(bx.const_undef(bx.reg_backend_type(&Reg::i32())))
-        }
-
-        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)
@@ -1222,7 +1218,7 @@ 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 {
+            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));
@@ -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 e11ebdce80f..16aad07194d 100644
--- a/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
@@ -597,7 +597,7 @@ 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 {
+            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);
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs
index f13b658b2ff..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_i32 {
+                    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_i32 {
+            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 2fcdf6ded98..35b1fefd286 100644
--- a/compiler/rustc_const_eval/src/interpret/terminator.rs
+++ b/compiler/rustc_const_eval/src/interpret/terminator.rs
@@ -215,8 +215,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 _ => false,
             }
         };
-        // Padding must be fully equal.
-        let pad_compat = || caller_abi.pad_i32 == callee_abi.pad_i32;
         // When comparing the PassMode, we have to be smart about comparing the attributes.
         let arg_attr_compat = |a1: &ArgAttributes, a2: &ArgAttributes| {
             // There's only one regular attribute that matters for the call ABI: InReg.
@@ -239,7 +237,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             (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 },
@@ -251,7 +249,7 @@ 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_target/src/abi/call/mips.rs b/compiler/rustc_target/src/abi/call/mips.rs
index ff8f3236214..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_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);
     }
diff --git a/compiler/rustc_target/src/abi/call/mod.rs b/compiler/rustc_target/src/abi/call/mod.rs
index 33f533e68f0..d2eb804d004 100644
--- a/compiler/rustc_target/src/abi/call/mod.rs
+++ b/compiler/rustc_target/src/abi/call/mod.rs
@@ -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(Box<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_i32: bool,
-
     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_i32: false, 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(Box::new(target.into()));
+        self.mode = PassMode::Cast(Box::new(target.into()), false);
     }
 
-    pub fn pad_with_i32(&mut self) {
-        self.pad_i32 = true;
+    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 {
@@ -737,6 +734,6 @@ 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>, 64);
-    static_assert_size!(FnAbi<'_, usize>, 88);
+    static_assert_size!(ArgAbi<'_, usize>, 56);
+    static_assert_size!(FnAbi<'_, usize>, 80);
 }
diff --git a/compiler/rustc_target/src/abi/call/sparc.rs b/compiler/rustc_target/src/abi/call/sparc.rs
index ff8f3236214..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_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);
     }
diff --git a/compiler/rustc_target/src/abi/call/x86.rs b/compiler/rustc_target/src/abi/call/x86.rs
index c2d70d1160c..7c26335dcf4 100644
--- a/compiler/rustc_target/src/abi/call/x86.rs
+++ b/compiler/rustc_target/src/abi/call/x86.rs
@@ -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)
                 }
             };