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.
64 lines
2.2 KiB
C++
64 lines
2.2 KiB
C++
// RUN: %clang_cc1 -triple i686-windows-msvc -emit-llvm -o - %s 2>&1 | FileCheck %s
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struct A {
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A();
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A(const A &);
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int x;
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};
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void decayToFp(int (*f)(A));
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void test() {
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auto ld = [](A a) {
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static int calls = 0;
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++calls;
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return a.x + calls;
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};
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decayToFp(ld);
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ld(A{});
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}
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// CHECK: define internal x86_thiscallcc noundef i32
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// CHECK-SAME: @"??R<lambda_0>@?0??test@@YAXXZ@QBE?A?<auto>@@UA@@@Z"
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// CHECK-SAME: (ptr noundef %this, ptr inalloca(<{ %struct.A }>) %[[ARG:.*]])
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// CHECK: %[[V:.*]] = getelementptr inbounds nuw <{ %struct.A }>, ptr %[[ARG]], i32 0, i32 0
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// CHECK: %call = call x86_thiscallcc noundef i32
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// CHECK-SAME: @"?__impl@<lambda_0>@?0??test@@YAXXZ@QBE?A?<auto>@@UA@@@Z"
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// CHECK-SAME: (ptr noundef %this, ptr dead_on_return noundef %[[V]])
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// CHECK: define internal noundef i32
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// CHECK-SAME: @"?__invoke@<lambda_0>@?0??test@@YAXXZ@CA?A?<auto>@@UA@@@Z"
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// CHECK-SAME: (ptr inalloca(<{ %struct.A }>) %[[ARG:.*]])
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// CHECK: %unused.capture = alloca %class.anon, align 1
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// CHECK: %[[VAR:.*]] = getelementptr inbounds nuw <{ %struct.A }>, ptr %[[ARG]], i32 0, i32 0
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// CHECK: %call = call x86_thiscallcc noundef i32
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// CHECK-SAME: @"?__impl@<lambda_0>@?0??test@@YAXXZ@QBE?A?<auto>@@UA@@@Z"
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// CHECK-SAME: (ptr noundef %unused.capture, ptr dead_on_return noundef %[[VAR]])
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// CHECK: ret i32 %call
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// CHECK: define internal x86_thiscallcc noundef i32
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// CHECK-SAME: @"?__impl@<lambda_0>@?0??test@@YAXXZ@QBE?A?<auto>@@UA@@@Z"
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// CHECK-SAME: (ptr noundef %this, ptr dead_on_return noundef %[[ARG:.*]])
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// CHECK: %this.addr = alloca ptr, align 4
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// CHECK: store ptr %this, ptr %this.addr, align 4
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// CHECK: %this1 = load ptr, ptr %this.addr, align 4
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// CHECK: %{{.*}} = load i32, ptr @"?calls@?1???R<lambda_0>
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// CHECK: %inc = add nsw i32 %{{.*}}, 1
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// CHECK: store i32 %inc, ptr @"?calls@?1???R<lambda_0>
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// CHECK: %{{.*}} = getelementptr inbounds nuw %struct.A, ptr %{{.*}}, i32 0, i32 0
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// CHECK: %{{.*}} = load i32, ptr %{{.*}}, align 4
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// CHECK: %{{.*}} = load i32, ptr @"?calls@?1???R<lambda_0>
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// CHECK: %add = add nsw i32 %{{.*}}, %{{.*}}
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// CHECK: ret i32 %add
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// Make sure we don't try to copy an uncopyable type.
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struct B {
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B();
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B(B &);
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void operator=(B);
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long long x;
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} b;
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void f() {
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[](B) {}(b);
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}
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