http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61095
Kostya Serebryany <kcc at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target|x86_64-*-* |
Priority|P3 |P1
Target Milestone|4.10.0 |---
Summary|[4.10 Regression] tsan is |miscompile: tsan is broken
|broken in gcc trunk, works |in gcc trunk, works in 4.9
|in 4.9 |
--- Comment #2 from Kostya Serebryany <kcc at gcc dot gnu.org> ---
fresh gcc optimizes away a piece of code. minimal repro:
int FOO(unsigned long addr) {
unsigned long *p = (unsigned long*)((addr & 0xffff83fffffffff8UL) * 4);
unsigned long xxx = (unsigned long)(p + 1);
return xxx >= 0x3c000000000UL;
}
gcc 4.9:
/usr/local/gcc-4.9.0/bin/gcc -S z.c -O2 -o - | grep -A 10 FOO:
FOO:
.LFB0:
.cfi_startproc
movabsq $-136339441844232, %rax
andq %rax, %rdi
movabsq $4123168604159, %rax
leaq 8(,%rdi,4), %rdx
cmpq %rax, %rdx
seta %al
movzbl %al, %eax
ret
trunk:
../gcc-inst/bin/gcc -S z.c -O2 -o - | grep -A 10 FOO:
FOO:
.LFB0:
.cfi_startproc
xorl %eax, %eax
ret
