[all-commits] [llvm/llvm-project] e18c6e: [clang] improve diagnostics for misaligned and lar...

[tschuett via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: e18c6ef6b41a59af73bf5c3d7d52a8c53a471e5d
      https://github.com/llvm/llvm-project/commit/e18c6ef6b41a59af73bf5c3d7d52a8c53a471e5d
  Author: Thorsten Schuett <schuett at gmail.com>
  Date:   2020-08-04 (Tue, 04 Aug 2020)

  Changed paths:
    M clang/include/clang/Basic/DiagnosticFrontendKinds.td
    M clang/include/clang/Basic/DiagnosticGroups.td
    M clang/lib/CodeGen/CGAtomic.cpp
    M clang/test/CodeGen/atomics-sema-alignment.c

  Log Message:
  -----------
  [clang] improve diagnostics for misaligned and large atomics

"Listing the alignment and access size (== expected alignment) in the warning
seems like a good idea."

solves PR 46947

  struct Foo {
    struct Bar {
      void * a;
      void * b;
    };
    Bar bar;
  };

  struct ThirtyTwo {
    struct Large {
      void * a;
      void * b;
      void * c;
      void * d;
    };
    Large bar;
  };

  void braz(Foo *foo, ThirtyTwo *braz) {
    Foo::Bar bar;
    __atomic_load(&foo->bar, &bar, __ATOMIC_RELAXED);

    ThirtyTwo::Large foobar;
    __atomic_load(&braz->bar, &foobar, __ATOMIC_RELAXED);
  }

repro.cpp:21:3: warning: misaligned atomic operation may incur significant performance penalty; the expected (16 bytes) exceeds the actual alignment (8 bytes) [-Watomic-alignment]
  __atomic_load(&foo->bar, &bar, __ATOMIC_RELAXED);
  ^
repro.cpp:24:3: warning: misaligned atomic operation may incur significant performance penalty; the expected (32 bytes) exceeds the actual alignment (8 bytes) [-Watomic-alignment]
  __atomic_load(&braz->bar, &foobar, __ATOMIC_RELAXED);
  ^
repro.cpp:24:3: warning: large atomic operation may incur significant performance penalty; the access size (32 bytes) exceeds the max lock-free size (16  bytes) [-Watomic-alignment]
3 warnings generated.

Differential Revision: https://reviews.llvm.org/D85102