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.
27 lines
855 B
C++
27 lines
855 B
C++
// RUN: %clang_cc1 -triple armv7-apple-ios -x c++ -emit-llvm -o - %s | FileCheck %s
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// RUN: %clang_cc1 -triple arm64-apple-ios -x c++ -emit-llvm -o - %s | FileCheck %s
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// According to the Itanium ABI (3.1.1), types with non-trivial copy
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// constructors passed by value should be passed indirectly, with the caller
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// creating a temporary.
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struct Empty;
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struct Empty {
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Empty(const Empty &e);
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bool check();
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};
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bool foo(Empty e) {
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// CHECK: @_Z3foo5Empty(ptr dead_on_return noundef %e)
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// CHECK: call {{.*}} @_ZN5Empty5checkEv(ptr {{[^,]*}} %e)
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return e.check();
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}
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void caller(Empty &e) {
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// CHECK: @_Z6callerR5Empty(ptr noundef nonnull align {{[0-9]+}} dereferenceable({{[0-9]+}}) %e)
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// CHECK: call {{.*}} @_ZN5EmptyC1ERKS_(ptr {{[^,]*}} [[NEWTMP:%.*]], ptr
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// CHECK: call {{.*}} @_Z3foo5Empty(ptr dead_on_return noundef [[NEWTMP]])
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foo(e);
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}
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