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158d72d728
Set the writable and dead_on_unwind attributes for sret arguments. These indicate that the argument points to writable memory (and it's legal to introduce spurious writes to it on entry to the function) and that the argument memory will not be used if the call unwinds. This enables additional MemCpyOpt/DSE/LICM optimizations.
74 lines
2.3 KiB
C++
74 lines
2.3 KiB
C++
// RUN: %clang_cc1 -fpass-by-value-is-noalias -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %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 %s -o - 2>&1 | FileCheck --check-prefix=NO_NOALIAS %s
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// A trivial struct large enough so it is not passed in registers on ARM64.
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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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int f;
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};
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// Make sure noalias is added to indirect arguments with trivially copyable types
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// if -fpass-by-value-is-noalias is provided.
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// WITH_NOALIAS: define{{.*}} void @_Z4take3Foo(ptr noalias noundef %arg)
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// NO_NOALIAS: define{{.*}} void @_Z4take3Foo(ptr noundef %arg)
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void take(Foo arg) {}
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int G;
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// NonTrivial is not trivially-copyable, because it has a non-trivial copy
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// constructor.
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struct NonTrivial {
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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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int f;
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NonTrivial(const NonTrivial &Other) {
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a = G + 10 + Other.a;
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}
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};
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// Make sure noalias is not added to indirect arguments that are not trivially
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// copyable even if -fpass-by-value-is-noalias is provided.
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// WITH_NOALIAS: define{{.*}} void @_Z4take10NonTrivial(ptr noundef %arg)
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// NO_NOALIAS: define{{.*}} void @_Z4take10NonTrivial(ptr noundef %arg)
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void take(NonTrivial arg) {}
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// Escape examples. Pointers to the objects passed to take() may escape, depending on whether a temporary copy is created or not (e.g. due to NRVO).
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struct A {
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A(A **where) : data{"hello world 1"} {
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*where = this; //Escaped pointer 1 (proposed UB?)
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}
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A() : data{"hello world 2"} {}
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char data[32];
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};
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A *p;
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// WITH_NOALIAS: define{{.*}} void @_Z4take1A(ptr noalias noundef %arg)
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// NO_NOALIAS: define{{.*}} void @_Z4take1A(ptr noundef %arg)
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void take(A arg) {}
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// WITH_NOALIAS: define{{.*}} void @_Z7CreateAPP1A(ptr dead_on_unwind noalias writable sret(%struct.A) align 1 %agg.result, ptr noundef %where)
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// NO_NOALIAS: define{{.*}} void @_Z7CreateAPP1A(ptr dead_on_unwind noalias writable sret(%struct.A) align 1 %agg.result, ptr noundef %where)
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A CreateA(A **where) {
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A justlikethis;
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*where = &justlikethis; //Escaped pointer 2 (should also be UB, then)
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return justlikethis;
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}
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// elsewhere, perhaps compiled by a smarter compiler that doesn't make a copy here
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void test() {
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take({&p}); // 1
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take(CreateA(&p)); // 2
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}
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