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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
57 lines
1.5 KiB
C++
57 lines
1.5 KiB
C++
// RUN: %clang_analyze_cc1 -std=c++14 -analyzer-checker=core \
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// RUN: -analyzer-config suppress-null-return-paths=false \
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// RUN: -verify %s
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// RUN: %clang_analyze_cc1 -std=c++14 -analyzer-checker=core \
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// RUN: -DSUPPRESSED \
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// RUN: -verify %s
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void clang_analyzer_eval(bool);
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typedef __typeof__(sizeof(int)) size_t;
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// These are ill-formed. One cannot return nullptr from a throwing version of an
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// operator new.
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void *operator new(size_t size) {
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return nullptr;
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// expected-warning@-1 {{'operator new' should not return a null pointer unless it is declared 'throw()' or 'noexcept'}}
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// expected-warning@-2 {{null returned from function that requires a non-null return value}}
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}
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void *operator new[](size_t size) {
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return nullptr;
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// expected-warning@-1 {{'operator new[]' should not return a null pointer unless it is declared 'throw()' or 'noexcept'}}
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// expected-warning@-2 {{null returned from function that requires a non-null return value}}
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}
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struct S {
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int x;
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S() : x(1) {}
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~S() {}
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int getX() const { return x; }
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};
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void testArrays() {
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S *s = new S[10]; // no-crash
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s[0].x = 2;
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#ifndef SUPPRESSED
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// expected-warning@-2 {{Dereference of null pointer}}
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#endif
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}
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void testCtor() {
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S *s = new S();
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s->x = 13;
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#ifndef SUPPRESSED
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// expected-warning@-2 {{Access to field 'x' results in a dereference of a null pointer (loaded from variable 's')}}
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#endif
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}
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void testMethod() {
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S *s = new S();
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const int X = s->getX();
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#ifndef SUPPRESSED
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// expected-warning@-2 {{Called C++ object pointer is null}}
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#endif
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}
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