diff options
| -rw-r--r-- | compiler/rustc_codegen_ssa/src/mir/rvalue.rs | 14 | ||||
| -rw-r--r-- | compiler/rustc_codegen_ssa/src/traits/builder.rs | 10 | ||||
| -rw-r--r-- | tests/codegen/intrinsics/transmute.rs | 37 |
3 files changed, 34 insertions, 27 deletions
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs index cbbb0196890..bf3b1e73b94 100644 --- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs +++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs @@ -207,9 +207,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { { // These cases are all UB to actually hit, so don't emit code for them. // (The size mismatches are reachable via `transmute_unchecked`.) - // We can't use unreachable because that's a terminator, and we - // need something that can be in the middle of a basic block. - bx.assume(bx.cx().const_bool(false)) + bx.unreachable_nonterminator(); } else { // Since in this path we have a place anyway, we can store or copy to it, // making sure we use the destination place's alignment even if the @@ -236,14 +234,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { || operand.layout.is_uninhabited() || cast.is_uninhabited() { - if !operand.layout.is_uninhabited() { - // Since this is known statically and the input could have existed - // without already having hit UB, might as well trap for it. - bx.abort(); - } + bx.unreachable_nonterminator(); - // Because this transmute is UB, return something easy to generate, - // since it's fine that later uses of the value are probably UB. + // We still need to return a value of the appropriate type, but + // it's already UB so do the easiest thing available. return OperandValue::poison(bx, cast); } diff --git a/compiler/rustc_codegen_ssa/src/traits/builder.rs b/compiler/rustc_codegen_ssa/src/traits/builder.rs index 9d367748c2a..0f1358ee508 100644 --- a/compiler/rustc_codegen_ssa/src/traits/builder.rs +++ b/compiler/rustc_codegen_ssa/src/traits/builder.rs @@ -136,6 +136,16 @@ pub trait BuilderMethods<'a, 'tcx>: ) -> Self::Value; fn unreachable(&mut self); + /// Like [`Self::unreachable`], but for use in the middle of a basic block. + fn unreachable_nonterminator(&mut self) { + // This is the preferred LLVM incantation for this per + // https://llvm.org/docs/Frontend/PerformanceTips.html#other-things-to-consider + // Other backends may override if they have a better way. + let const_true = self.cx().const_bool(true); + let poison_ptr = self.const_poison(self.cx().type_ptr()); + self.store(const_true, poison_ptr, Align::ONE); + } + fn add(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value; fn fadd(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value; fn fadd_fast(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value; diff --git a/tests/codegen/intrinsics/transmute.rs b/tests/codegen/intrinsics/transmute.rs index e375724bc1b..c9a1cd58af3 100644 --- a/tests/codegen/intrinsics/transmute.rs +++ b/tests/codegen/intrinsics/transmute.rs @@ -29,28 +29,28 @@ pub struct Aggregate8(u8); // CHECK-LABEL: @check_bigger_size( #[no_mangle] pub unsafe fn check_bigger_size(x: u16) -> u32 { - // CHECK: call void @llvm.assume(i1 false) + // CHECK: store i1 true, ptr poison, align 1 transmute_unchecked(x) } // CHECK-LABEL: @check_smaller_size( #[no_mangle] pub unsafe fn check_smaller_size(x: u32) -> u16 { - // CHECK: call void @llvm.assume(i1 false) + // CHECK: store i1 true, ptr poison, align 1 transmute_unchecked(x) } // CHECK-LABEL: @check_smaller_array( #[no_mangle] pub unsafe fn check_smaller_array(x: [u32; 7]) -> [u32; 3] { - // CHECK: call void @llvm.assume(i1 false) + // CHECK: store i1 true, ptr poison, align 1 transmute_unchecked(x) } // CHECK-LABEL: @check_bigger_array( #[no_mangle] pub unsafe fn check_bigger_array(x: [u32; 3]) -> [u32; 7] { - // CHECK: call void @llvm.assume(i1 false) + // CHECK: store i1 true, ptr poison, align 1 transmute_unchecked(x) } @@ -58,9 +58,9 @@ pub unsafe fn check_bigger_array(x: [u32; 3]) -> [u32; 7] { #[no_mangle] #[custom_mir(dialect = "runtime", phase = "optimized")] pub unsafe fn check_to_empty_array(x: [u32; 5]) -> [u32; 0] { - // CHECK-NOT: trap - // CHECK: call void @llvm.trap - // CHECK-NOT: trap + // CHECK: start + // CHECK-NEXT: store i1 true, ptr poison, align 1 + // CHECK-NEXT: ret void mir! { { RET = CastTransmute(x); @@ -73,9 +73,9 @@ pub unsafe fn check_to_empty_array(x: [u32; 5]) -> [u32; 0] { #[no_mangle] #[custom_mir(dialect = "runtime", phase = "optimized")] pub unsafe fn check_from_empty_array(x: [u32; 0]) -> [u32; 5] { - // CHECK-NOT: call - // CHECK: call void @llvm.assume(i1 false) - // CHECK-NOT: call + // CHECK: start + // CHECK-NEXT: store i1 true, ptr poison, align 1 + // CHECK-NEXT: ret void mir! { { RET = CastTransmute(x); @@ -88,9 +88,9 @@ pub unsafe fn check_from_empty_array(x: [u32; 0]) -> [u32; 5] { #[no_mangle] #[custom_mir(dialect = "runtime", phase = "optimized")] pub unsafe fn check_to_uninhabited(x: u16) { - // CHECK-NOT: trap - // CHECK: call void @llvm.trap - // CHECK-NOT: trap + // CHECK: start + // CHECK-NEXT: store i1 true, ptr poison, align 1 + // CHECK-NEXT: ret void mir! { let temp: BigNever; { @@ -104,7 +104,9 @@ pub unsafe fn check_to_uninhabited(x: u16) { #[no_mangle] #[custom_mir(dialect = "runtime", phase = "optimized")] pub unsafe fn check_from_uninhabited(x: BigNever) -> u16 { - // CHECK: ret i16 poison + // CHECK: start + // CHECK-NEXT: store i1 true, ptr poison, align 1 + // CHECK-NEXT: ret i16 poison mir! { { RET = CastTransmute(x); @@ -401,9 +403,9 @@ pub unsafe fn check_issue_109992(x: ()) -> [(); 1] { pub unsafe fn check_unit_to_never(x: ()) { // This uses custom MIR to avoid MIR optimizations having removed ZST ops. - // CHECK-NOT: trap - // CHECK: call void @llvm.trap - // CHECK-NOT: trap + // CHECK: start + // CHECK-NEXT: store i1 true, ptr poison, align 1 + // CHECK-NEXT: ret void mir! { let temp: ZstNever; { @@ -420,6 +422,7 @@ pub unsafe fn check_unit_from_never(x: ZstNever) -> () { // This uses custom MIR to avoid MIR optimizations having removed ZST ops. // CHECK: start + // CHECK-NEXT: store i1 true, ptr poison, align 1 // CHECK-NEXT: ret void mir! { { |