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.
30 lines
584 B
C++
30 lines
584 B
C++
// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -emit-llvm -o - %s | FileCheck %s
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struct Foo {
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Foo();
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Foo(const Foo&);
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};
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struct Bar {
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Bar();
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operator const Foo&() const;
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};
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void f(Foo);
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// CHECK-LABEL: define{{.*}} void @_Z1g3Foo(ptr dead_on_return noundef %foo)
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void g(Foo foo) {
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// CHECK: call void @_ZN3BarC1Ev
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// CHECK: @_ZNK3BarcvRK3FooEv
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// CHECK: call void @_Z1f3Foo
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f(Bar());
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// CHECK: call void @_ZN3FooC1Ev
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// CHECK: call void @_Z1f3Foo
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f(Foo());
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// CHECK: call void @_ZN3FooC1ERKS_
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// CHECK: call void @_Z1f3Foo
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f(foo);
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// CHECK: ret
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}
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