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Summary: Right now we annotate C++'s `operator new` with `noalias` attribute, which very much is healthy for optimizations. However as per [[ http://eel.is/c++draft/basic.stc.dynamic.allocation | `[basic.stc.dynamic.allocation]` ]], there are more promises on global `operator new`, namely: * non-`std::nothrow_t` `operator new` *never* returns `nullptr` * If `std::align_val_t align` parameter is taken, the pointer will also be `align`-aligned * ~~global `operator new`-returned pointer is `__STDCPP_DEFAULT_NEW_ALIGNMENT__`-aligned ~~ It's more caveated than that. Supplying this information may not cause immediate landslide effects on any specific benchmarks, but it for sure will be healthy for optimizer in the sense that the IR will better reflect the guarantees provided in the source code. The caveat is `-fno-assume-sane-operator-new`, which currently prevents emitting `noalias` attribute, and is automatically passed by Sanitizers ([[ https://bugs.llvm.org/show_bug.cgi?id=16386 | PR16386 ]]) - should it also cover these attributes? The problem is that the flag is back-end-specific, as seen in `test/Modules/explicit-build-flags.cpp`. But while it is okay to add `noalias` metadata in backend, we really should be adding at least the alignment metadata to the AST, since that allows us to perform sema checks on it. Reviewers: erichkeane, rjmccall, jdoerfert, eugenis, rsmith Reviewed By: rsmith Subscribers: xbolva00, jrtc27, atanasyan, nlopes, cfe-commits Tags: #llvm, #clang Differential Revision: https://reviews.llvm.org/D73380
72 lines
2.2 KiB
C++
72 lines
2.2 KiB
C++
// RUN: %clang_cc1 -triple i686-pc-linux-gnu %s -o - -emit-llvm -verify | FileCheck %s
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// expected-no-diagnostics
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typedef __typeof(sizeof(int)) size_t;
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namespace test1 {
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struct A { void operator delete(void*,size_t); int x; };
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// CHECK-LABEL: define void @_ZN5test11aEPNS_1AE(
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void a(A *x) {
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// CHECK: load
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// CHECK-NEXT: icmp eq {{.*}}, null
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// CHECK-NEXT: br i1
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// CHECK: call void @_ZN5test11AdlEPvj(i8* %{{.*}}, i32 4)
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delete x;
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}
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}
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// Check that we make cookies for the two-arg delete even when using
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// the global allocator and deallocator.
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namespace test2 {
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struct A {
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int x;
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void *operator new[](size_t);
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void operator delete[](void *, size_t);
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};
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// CHECK: define [[A:%.*]]* @_ZN5test24testEv()
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A *test() {
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// CHECK: [[NEW:%.*]] = call noalias nonnull i8* @_Znaj(i32 44)
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// CHECK-NEXT: [[T0:%.*]] = bitcast i8* [[NEW]] to i32*
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// CHECK-NEXT: store i32 10, i32* [[T0]]
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// CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds i8, i8* [[NEW]], i32 4
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// CHECK-NEXT: [[T2:%.*]] = bitcast i8* [[T1]] to [[A]]*
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// CHECK-NEXT: ret [[A]]* [[T2]]
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return ::new A[10];
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}
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// CHECK-LABEL: define void @_ZN5test24testEPNS_1AE(
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void test(A *p) {
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// CHECK: [[P:%.*]] = alloca [[A]]*, align 4
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// CHECK-NEXT: store [[A]]* {{%.*}}, [[A]]** [[P]], align 4
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// CHECK-NEXT: [[T0:%.*]] = load [[A]]*, [[A]]** [[P]], align 4
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// CHECK-NEXT: [[T1:%.*]] = icmp eq [[A]]* [[T0]], null
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// CHECK-NEXT: br i1 [[T1]],
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// CHECK: [[T2:%.*]] = bitcast [[A]]* [[T0]] to i8*
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// CHECK-NEXT: [[T3:%.*]] = getelementptr inbounds i8, i8* [[T2]], i32 -4
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// CHECK-NEXT: [[T4:%.*]] = bitcast i8* [[T3]] to i32*
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// CHECK-NEXT: [[T5:%.*]] = load i32, i32* [[T4]]
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// CHECK-NEXT: call void @_ZdaPv(i8* [[T3]])
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// CHECK-NEXT: br label
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::delete[] p;
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}
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}
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// rdar://problem/8913519
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namespace test3 {
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struct A {
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int x;
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void operator delete[](void *, size_t);
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};
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struct B : A {};
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// CHECK-LABEL: define void @_ZN5test34testEv()
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void test() {
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// CHECK: [[CALL:%.*]] = call noalias nonnull i8* @_Znaj(i32 24)
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// CHECK-NEXT: bitcast i8* [[CALL]] to i32*
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// CHECK-NEXT: store i32 5
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(void) new B[5];
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}
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}
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