9e0c06d708
Let Clang emit `dead_on_return` attribute on pointer arguments that are passed indirectly, namely, large aggregates that the ABI mandates be passed by value; thus, the parameter is destroyed within the callee. Writes to such arguments are not observable by the caller after the callee returns. This should desirably enable further MemCpyOpt/DSE optimizations. Previous discussion: https://discourse.llvm.org/t/rfc-add-dead-on-return-attribute/86871.
32 lines
1.1 KiB
C
32 lines
1.1 KiB
C
// RUN: %clang_cc1 -w -triple x86_64-pc-win32 -emit-llvm -o - %s | FileCheck %s
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// To be ABI compatible with code generated by MSVC, there shouldn't be any
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// sign/zero extensions on types smaller than 64bit.
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// CHECK-LABEL: define dso_local void @f1(i8 noundef %a)
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void f1(char a) {}
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// CHECK-LABEL: define dso_local void @f2(i8 noundef %a)
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void f2(unsigned char a) {}
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// CHECK-LABEL: define dso_local void @f3(i16 noundef %a)
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void f3(short a) {}
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// CHECK-LABEL: define dso_local void @f4(i16 noundef %a)
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void f4(unsigned short a) {}
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// For ABI compatibility with ICC, _Complex should be passed/returned
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// as if it were a struct with two elements.
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// CHECK-LABEL: define dso_local void @f5(i64 noundef %a.coerce)
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void f5(_Complex float a) {}
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// CHECK-LABEL: define dso_local void @f6(ptr dead_on_return noundef %a)
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void f6(_Complex double a) {}
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// CHECK-LABEL: define dso_local i64 @f7()
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_Complex float f7(void) { return 1.0; }
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// CHECK-LABEL: define dso_local void @f8(ptr dead_on_unwind noalias writable sret({ double, double }) align 8 %agg.result)
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_Complex double f8(void) { return 1.0; }
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