llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-clang Author: None (javiermunozkirschberg) <details> <summary>Changes</summary> Pull request #<!-- -->139973 created a very useful warning for detecting not return value optimizations. This can be seen as useful for two different audiences: _compiler developers_, who may see cases where no optimization is done, and _compiler users_ who can detect when there is no copy elision. In C++ this makes a lot of sense - the effect of not having copy elision is not only performance impact, but it can be seen in the execution of code (like the copy constructor or the assignment operator) that may not be executed otherwise. However, the value for compiler users with regards to plain C code is more difficult for me to assert. Specifically, in C it's only about a missing optimization - and can pollute your code with this new warning. GCC, for instance, restrict -Wnrvo to C++. The following pull request will restrict Wnrvo so it does not warn on plain C-code. Change-Id: Iaadd60f072c176972a5210c1fd1a6f0499d3ff39 --- Full diff: https://github.com/llvm/llvm-project/pull/157059.diff 3 Files Affected: - (modified) clang/docs/ReleaseNotes.rst (+1) - (modified) clang/lib/Sema/SemaDecl.cpp (+2) - (added) clang/test/SemaCXX/no-warn-nrvo-on-c.c (+41) ``````````diff diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 780e8a31cae6d..1a4d1b9e26d4d 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -223,6 +223,7 @@ Deprecated Compiler Flags Modified Compiler Flags ----------------------- - The `-gkey-instructions` compiler flag is now enabled by default when DWARF is emitted for plain C/C++ and optimizations are enabled. (#GH149509) +- The `-Wnrvo` compiler flag will not apply for C language. Removed Compiler Flags ------------------------- diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp index 12bedae05f6f3..0c96e9dd16b07 100644 --- a/clang/lib/Sema/SemaDecl.cpp +++ b/clang/lib/Sema/SemaDecl.cpp @@ -16169,6 +16169,8 @@ void Sema::applyFunctionAttributesBeforeParsingBody(Decl *FD) { } void Sema::computeNRVO(Stmt *Body, FunctionScopeInfo *Scope) { + if (!getLangOpts().CPlusPlus) + return; ReturnStmt **Returns = Scope->Returns.data(); for (unsigned I = 0, E = Scope->Returns.size(); I != E; ++I) { diff --git a/clang/test/SemaCXX/no-warn-nrvo-on-c.c b/clang/test/SemaCXX/no-warn-nrvo-on-c.c new file mode 100644 index 0000000000000..a8173e51faceb --- /dev/null +++ b/clang/test/SemaCXX/no-warn-nrvo-on-c.c @@ -0,0 +1,41 @@ +// RUN: %clang -std=c23 -Wnrvo -Xclang -verify %s +// expected-no-diagnostics + +#include <stdlib.h> + +#define SIZE 20 + +typedef struct String_s { + char* buf; + size_t len; +} String; + + +void clean(String* s) { + free(s->buf); +} + +String randomString() { + String s = {}; + + s.buf = malloc(SIZE); + s.len = SIZE; + + if (!s.buf) { + goto fail; + } + + return s; + +fail: + clean(&s); + return (String){}; +} + +int main(int argc, char** argv) +{ + String s= randomString(); + clean(&s); + + return 0; +} `````````` </details> https://github.com/llvm/llvm-project/pull/157059 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
