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.
21 lines
630 B
C++
21 lines
630 B
C++
// RUN: %clang_cc1 -no-enable-noundef-analysis -triple i386-unknown-unknown -emit-llvm -o - %s | FileCheck %s
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void __attribute__((fastcall)) foo1(int &y);
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void bar1(int &y) {
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// CHECK-LABEL: define{{.*}} void @_Z4bar1Ri
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// CHECK: call x86_fastcallcc void @_Z4foo1Ri(ptr inreg nonnull align {{[0-9]+}} dereferenceable({{[0-9]+}}) %
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foo1(y);
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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__((fastcall)) foo2(S1 a, int b);
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void bar2(S1 a, int b) {
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// CHECK-LABEL: define{{.*}} void @_Z4bar22S1i
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// CHECK: call x86_fastcallcc void @_Z4foo22S1i(ptr dead_on_return inreg %{{.*}}, i32 inreg %
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foo2(a, b);
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}
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