------- Comment #10 from ubizjak at gmail dot com 2008-09-12 18:03 -------
This is in fact undefined code. When Transform4x4() gets inlined in fun(), you
are accessing pAR[0] (aliased to *pMatrix) as "short" and as __m128i. Since
-fstrict-aliasing (the default) assumes that "short" can't alias __m128i, gcc
reorders stores and loads to the same address at will.
This is the diff between -fstrict-aliasing (t_.s) and -fno-strict-aliasing
(t.s):
--- t.s 2008-09-12 19:27:23.000000000 +0200
+++ t_.s 2008-09-12 19:27:04.000000000 +0200
@@ -68,6 +68,7 @@
movq 8(%rsp), %rax
movq %xmm2, 32(%rdi)
movq %xmm5, 64(%rdi)
+ movw $0, (%rdi)
movq %xmm0, 96(%rdi)
movl %eax, %esi
movq %rax, %rcx
@@ -77,10 +78,9 @@
shrq $48, %rdx
testw %si, %si
movq %rax, (%rdi)
- movw $0, (%rdi)
+ movl $.LC0, %edi
setne %sil
cmpw $1, %cx
- movl $.LC0, %edi
movzbl %sil, %esi
sbbl $-1, %esi
cmpw $1, %dx
You can see that store of 0 to (%rdi) has been moved above store of %rax to the
same address. You should use unions to fix your code.
--
ubizjak at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution| |INVALID
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37096
