Rollup merge of #137894 - compiler-errors:no-scalar-pair-opt, r=oli-obk

Revert "store ScalarPair via memset when one side is undef and the other side can be memset"

cc #137892
reverts #135335

r? oli-obk

3 files changed, 24 insertions, 62 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs
index 4b33bdeadba..acae09b2c25 100644
--- a/compiler/rustc_codegen_ssa/src/mir/operand.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/operand.rs
@@ -203,30 +203,14 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
         let alloc_align = alloc.inner().align;
         assert!(alloc_align >= layout.align.abi);
 
-        // Returns `None` when the value is partially undefined or any byte of it has provenance.
-        // Otherwise returns the value or (if the entire value is undef) returns an undef.
         let read_scalar = |start, size, s: abi::Scalar, ty| {
-            let range = alloc_range(start, size);
             match alloc.0.read_scalar(
                 bx,
-                range,
+                alloc_range(start, size),
                 /*read_provenance*/ matches!(s.primitive(), abi::Primitive::Pointer(_)),
             ) {
-                Ok(val) => Some(bx.scalar_to_backend(val, s, ty)),
-                Err(_) => {
-                    // We may have failed due to partial provenance or unexpected provenance,
-                    // continue down the normal code path if so.
-                    if alloc.0.provenance().range_empty(range, &bx.tcx())
-                        // Since `read_scalar` failed, but there were no relocations involved, the
-                        // bytes must be partially or fully uninitialized. Thus we can now unwrap the
-                        // information about the range of uninit bytes and check if it's the full range.
-                        && alloc.0.init_mask().is_range_initialized(range).unwrap_err() == range
-                    {
-                        Some(bx.const_undef(ty))
-                    } else {
-                        None
-                    }
-                }
+                Ok(val) => bx.scalar_to_backend(val, s, ty),
+                Err(_) => bx.const_poison(ty),
             }
         };
 
@@ -237,14 +221,16 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
         // check that walks over the type of `mplace` to make sure it is truly correct to treat this
         // like a `Scalar` (or `ScalarPair`).
         match layout.backend_repr {
-            BackendRepr::Scalar(s) => {
+            BackendRepr::Scalar(s @ abi::Scalar::Initialized { .. }) => {
                 let size = s.size(bx);
                 assert_eq!(size, layout.size, "abi::Scalar size does not match layout size");
-                if let Some(val) = read_scalar(offset, size, s, bx.immediate_backend_type(layout)) {
-                    return OperandRef { val: OperandValue::Immediate(val), layout };
-                }
+                let val = read_scalar(offset, size, s, bx.immediate_backend_type(layout));
+                OperandRef { val: OperandValue::Immediate(val), layout }
             }
-            BackendRepr::ScalarPair(a, b) => {
+            BackendRepr::ScalarPair(
+                a @ abi::Scalar::Initialized { .. },
+                b @ abi::Scalar::Initialized { .. },
+            ) => {
                 let (a_size, b_size) = (a.size(bx), b.size(bx));
                 let b_offset = (offset + a_size).align_to(b.align(bx).abi);
                 assert!(b_offset.bytes() > 0);
@@ -260,21 +246,20 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
                     b,
                     bx.scalar_pair_element_backend_type(layout, 1, true),
                 );
-                if let (Some(a_val), Some(b_val)) = (a_val, b_val) {
-                    return OperandRef { val: OperandValue::Pair(a_val, b_val), layout };
-                }
+                OperandRef { val: OperandValue::Pair(a_val, b_val), layout }
+            }
+            _ if layout.is_zst() => OperandRef::zero_sized(layout),
+            _ => {
+                // Neither a scalar nor scalar pair. Load from a place
+                // FIXME: should we cache `const_data_from_alloc` to avoid repeating this for the
+                // same `ConstAllocation`?
+                let init = bx.const_data_from_alloc(alloc);
+                let base_addr = bx.static_addr_of(init, alloc_align, None);
+
+                let llval = bx.const_ptr_byte_offset(base_addr, offset);
+                bx.load_operand(PlaceRef::new_sized(llval, layout))
             }
-            _ if layout.is_zst() => return OperandRef::zero_sized(layout),
-            _ => {}
         }
-        // Neither a scalar nor scalar pair. Load from a place
-        // FIXME: should we cache `const_data_from_alloc` to avoid repeating this for the
-        // same `ConstAllocation`?
-        let init = bx.const_data_from_alloc(alloc);
-        let base_addr = bx.static_addr_of(init, alloc_align, None);
-
-        let llval = bx.const_ptr_byte_offset(base_addr, offset);
-        bx.load_operand(PlaceRef::new_sized(llval, layout))
     }
 
     /// Asserts that this operand refers to a scalar and returns
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index 67555d40332..ff555f4273c 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -8,7 +8,7 @@ use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
 use rustc_middle::{bug, mir, span_bug};
 use rustc_session::config::OptLevel;
 use rustc_span::{DUMMY_SP, Span};
-use tracing::{debug, instrument, trace};
+use tracing::{debug, instrument};
 
 use super::operand::{OperandRef, OperandValue};
 use super::place::PlaceRef;
@@ -93,8 +93,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     return;
                 }
 
-                // If `v` is an integer constant whose value is just a single byte repeated N times,
-                // emit a `memset` filling the entire `dest` with that byte.
                 let try_init_all_same = |bx: &mut Bx, v| {
                     let start = dest.val.llval;
                     let size = bx.const_usize(dest.layout.size.bytes());
@@ -119,33 +117,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     false
                 };
 
-                trace!(?cg_elem.val);
                 match cg_elem.val {
                     OperandValue::Immediate(v) => {
                         if try_init_all_same(bx, v) {
                             return;
                         }
                     }
-                    OperandValue::Pair(a, b) => {
-                        let a_is_undef = bx.cx().is_undef(a);
-                        match (a_is_undef, bx.cx().is_undef(b)) {
-                            // Can happen for uninit unions
-                            (true, true) => {
-                                // FIXME: can we produce better output here?
-                            }
-                            (false, true) | (true, false) => {
-                                let val = if a_is_undef { b } else { a };
-                                if try_init_all_same(bx, val) {
-                                    return;
-                                }
-                            }
-                            (false, false) => {
-                                // FIXME: if both are the same value, use try_init_all_same
-                            }
-                        }
-                    }
-                    OperandValue::ZeroSized => unreachable!("checked above"),
-                    OperandValue::Ref(..) => {}
+                    _ => (),
                 }
 
                 let count = self
diff --git a/compiler/rustc_codegen_ssa/src/traits/consts.rs b/compiler/rustc_codegen_ssa/src/traits/consts.rs
index 5cfb56ebace..dc6b68ceff7 100644
--- a/compiler/rustc_codegen_ssa/src/traits/consts.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/consts.rs
@@ -9,7 +9,6 @@ pub trait ConstCodegenMethods<'tcx>: BackendTypes {
     /// Generate an uninitialized value (matching uninitialized memory in MIR).
     /// Whether memory is initialized or not is tracked byte-for-byte.
     fn const_undef(&self, t: Self::Type) -> Self::Value;
-    fn is_undef(&self, v: Self::Value) -> bool;
     /// Generate a fake value. Poison always affects the entire value, even if just a single byte is
     /// poison. This can only be used in codepaths that are already UB, i.e., UB-free Rust code
     /// (including code that e.g. copies uninit memory with `MaybeUninit`) can never encounter a