[llvm-bugs] [Bug 34214] New: clang does not support 64bit gcc atomics on ia32

via llvm-bugs llvm-bugs at lists.llvm.org
Wed Aug 16 13:34:09 PDT 2017


            Bug ID: 34214
           Summary: clang does not support 64bit  gcc atomics on ia32
           Product: clang
           Version: 5.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: raj.khem at gmail.com
                CC: llvm-bugs at lists.llvm.org

#include <stdint.h>
# define p_atomic_add(v, i) (void) __atomic_add_fetch((v), (i),
# define p_atomic_add(v, i) (void) __sync_add_and_fetch((v), (i))

void foo(uint64_t* a, uint64_t b)
        p_atomic_add(a, b);


clang -std=gnu11 -m32 -march=i586 -S -O2 a.c -DUSE_GCC_ATOMIC_BUILTINS

produces a call to __atomic_fetch_add_8

but same compiled with gcc resolves correctly ( uses lock cmpxchg8b )

if I use -march=i386 then same code is generated with gcc as well but thats
expected since cmpxchg8b doesnt exist on i386

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