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
1.1 KiB
C++
30 lines
1.1 KiB
C++
// RUN: %clang_cc1 -triple x86_64-unknown-windows -emit-llvm -target-cpu core2 -o - %s | FileCheck %s
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#define SWIFTCALL __attribute__((swiftcall))
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#define OUT __attribute__((swift_indirect_result))
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#define ERROR __attribute__((swift_error_result))
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#define CONTEXT __attribute__((swift_context))
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/*****************************************************************************/
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/****************************** PARAMETER ABIS *******************************/
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/*****************************************************************************/
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// Swift doesn't use inalloca like windows x86 normally does.
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struct NonTrivial {
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NonTrivial();
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NonTrivial(const NonTrivial &);
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int o;
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};
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SWIFTCALL int receiveNonTrivial(NonTrivial o) { return o.o; }
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// CHECK-LABEL: define dso_local swiftcc noundef i32 @"?receiveNonTrivial@@YSHUNonTrivial@@@Z"(ptr dead_on_return noundef %o)
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int passNonTrivial() {
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return receiveNonTrivial({});
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}
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// CHECK-LABEL: define dso_local noundef i32 @"?passNonTrivial@@YAHXZ"()
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// CHECK-NOT: stacksave
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// CHECK: call swiftcc noundef i32 @"?receiveNonTrivial@@YSHUNonTrivial@@@Z"(ptr dead_on_return noundef %{{.*}})
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