Propagate ScalarPair for any type.

Author: cjgillot

compiler/rustc_mir_transform/src/const_prop.rs

@@ -581,40 +581,22 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                 Some(self.operand_from_scalar(scalar, value.layout.ty))
             }
             Immediate::ScalarPair(..) => {
-                // Found a value represented as a pair. For now only do const-prop if the type
-                // of `rvalue` is also a tuple with two scalars.
-                // FIXME: enable the general case stated above ^.
-                let ty = value.layout.ty;
-                // Only do it for tuples
-                let ty::Tuple(types) = ty.kind() else { return None };
-                // Only do it if tuple is also a pair with two scalars
-                if let [ty1, ty2] = types[..] {
-                    let ty_is_scalar = |ty| {
-                        self.ecx.layout_of(ty).ok().map(|layout| layout.abi.is_scalar())
-                            == Some(true)
-                    };
-                    let alloc = if ty_is_scalar(ty1) && ty_is_scalar(ty2) {
-                        self.ecx
-                            .intern_with_temp_alloc(value.layout, |ecx, dest| {
-                                ecx.write_immediate(*imm, dest)
-                            })
-                            .unwrap()
-                    } else {
-                        return None;
-                    };
-
-                    // Assign entire constant in a single statement.
-                    // We can't use aggregates, as we run after the aggregate-lowering `MirPhase`.
-                    let const_val = ConstValue::ByRef { alloc, offset: Size::ZERO };
-                    let literal = ConstantKind::Val(const_val, ty);
-                    Some(Operand::Constant(Box::new(Constant {
-                        span: DUMMY_SP,
-                        user_ty: None,
-                        literal,
-                    })))
-                } else {
-                    None
-                }
+                let alloc = self
+                    .ecx
+                    .intern_with_temp_alloc(value.layout, |ecx, dest| {
+                        ecx.write_immediate(*imm, dest)
+                    })
+                    .ok()?;
+
+                let literal = ConstantKind::Val(
+                    ConstValue::ByRef { alloc, offset: Size::ZERO },
+                    value.layout.ty,
+                );
+                Some(Operand::Constant(Box::new(Constant {
+                    span: DUMMY_SP,
+                    user_ty: None,
+                    literal,
+                })))
             }
             // Scalars or scalar pairs that contain undef values are assumed to not have
             // successfully evaluated and are thus not propagated.

tests/mir-opt/const_prop/issue_66971.main.ConstProp.panic-abort.diff

@@ -8,8 +8,10 @@
 
       bb0: {
           StorageLive(_2);
-          _2 = (const (), const 0_u8, const 0_u8);
-          _1 = encode(move _2) -> [return: bb1, unwind unreachable];
+-         _2 = (const (), const 0_u8, const 0_u8);
+-         _1 = encode(move _2) -> [return: bb1, unwind unreachable];
++         _2 = const ((), 0_u8, 0_u8);
++         _1 = encode(const ((), 0_u8, 0_u8)) -> [return: bb1, unwind unreachable];
       }
 
       bb1: {

tests/mir-opt/const_prop/issue_66971.main.ConstProp.panic-unwind.diff

@@ -8,8 +8,10 @@
 
       bb0: {
           StorageLive(_2);
-          _2 = (const (), const 0_u8, const 0_u8);
-          _1 = encode(move _2) -> [return: bb1, unwind continue];
+-         _2 = (const (), const 0_u8, const 0_u8);
+-         _1 = encode(move _2) -> [return: bb1, unwind continue];
++         _2 = const ((), 0_u8, 0_u8);
++         _1 = encode(const ((), 0_u8, 0_u8)) -> [return: bb1, unwind continue];
       }
 
       bb1: {

tests/mir-opt/const_prop/issue_67019.main.ConstProp.panic-abort.diff

@@ -13,9 +13,10 @@
 -         _3 = (const 1_u8, const 2_u8);
 -         _2 = (move _3,);
 +         _3 = const (1_u8, 2_u8);
-+         _2 = (const (1_u8, 2_u8),);
++         _2 = const ((1_u8, 2_u8),);
           StorageDead(_3);
-          _1 = test(move _2) -> [return: bb1, unwind unreachable];
+-         _1 = test(move _2) -> [return: bb1, unwind unreachable];
++         _1 = test(const ((1_u8, 2_u8),)) -> [return: bb1, unwind unreachable];
       }
 
       bb1: {

tests/mir-opt/const_prop/issue_67019.main.ConstProp.panic-unwind.diff

@@ -13,9 +13,10 @@
 -         _3 = (const 1_u8, const 2_u8);
 -         _2 = (move _3,);
 +         _3 = const (1_u8, 2_u8);
-+         _2 = (const (1_u8, 2_u8),);
++         _2 = const ((1_u8, 2_u8),);
           StorageDead(_3);
-          _1 = test(move _2) -> [return: bb1, unwind continue];
+-         _1 = test(move _2) -> [return: bb1, unwind continue];
++         _1 = test(const ((1_u8, 2_u8),)) -> [return: bb1, unwind continue];
       }
 
       bb1: {