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.
39 lines
791 B
C++
39 lines
791 B
C++
// RUN: %clang_cc1 -triple i386-unknown-unknown %s -emit-llvm -o - | FileCheck %s
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// CHECK: _Z3fooRi(ptr inreg
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void __attribute__ ((regparm (1))) foo(int &a) {
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}
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struct S1 {
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int x;
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S1(const S1 &y);
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};
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void __attribute__((regparm(3))) foo2(S1 a, int b);
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// CHECK: declare void @_Z4foo22S1i(ptr dead_on_return inreg noundef, i32 inreg noundef)
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void bar2(S1 a, int b) {
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foo2(a, b);
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}
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struct S2 {
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int x;
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};
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void __attribute__((regparm(3))) foo3(struct S2 a, int b);
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// CHECK: declare void @_Z4foo32S2i(i32 inreg, i32 inreg noundef)
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void bar3(struct S2 a, int b) {
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foo3(a, b);
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}
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struct S3 {
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struct {
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struct {} b[0];
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} a;
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};
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__attribute((regparm(2))) void foo4(S3 a, int b);
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// CHECK: declare void @_Z4foo42S3i(i32 inreg noundef)
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void bar3(S3 a, int b) {
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foo4(a, b);
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}
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