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.
23 lines
893 B
Objective-C
23 lines
893 B
Objective-C
// RUN: %clang_cc1 -fpass-by-value-is-noalias -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns -fobjc-runtime-has-weak -fobjc-arc -fobjc-dispatch-method=mixed %s -o - 2>&1 | FileCheck --check-prefix=WITH_NOALIAS %s
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// RUN: %clang_cc1 -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns -fobjc-runtime-has-weak -fobjc-arc -fobjc-dispatch-method=mixed %s -o - 2>&1 | FileCheck --check-prefix=NO_NOALIAS %s
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@interface Bar
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@property char value;
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@end
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// A struct large enough so it is not passed in registers on ARM64, but with a
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// weak reference, so noalias should not be added even with
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// -fpass-by-value-is-noalias.
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struct Foo {
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int a;
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int b;
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int c;
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int d;
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int e;
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Bar *__weak f;
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};
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// WITH_NOALIAS: define{{.*}} void @take(ptr dead_on_return noundef %arg)
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// NO_NOALIAS: define{{.*}} void @take(ptr dead_on_return noundef %arg)
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void take(struct Foo arg) {}
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