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other/8553: AltiVec vec_abs broken at -O0 with register keyword
- From: hartwood at crosslink dot net
- To: gcc-gnats at gcc dot gnu dot org
- Date: 12 Nov 2002 19:25:59 -0000
- Subject: other/8553: AltiVec vec_abs broken at -O0 with register keyword
- Reply-to: hartwood at crosslink dot net
>Number: 8553
>Category: other
>Synopsis: AltiVec vec_abs broken at -O0 with register keyword
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: wrong-code
>Submitter-Id: net
>Arrival-Date: Tue Nov 12 11:36:05 PST 2002
>Closed-Date:
>Last-Modified:
>Originator: Rick Cellucci
>Release: gcc version 3.3 20021104 (experimental)
>Organization:
>Environment:
Configured with: ../gcc3.3/configure --prefix=/usr/local/darwin --enable-altivec --enable-languages=c --with-cpu=7400 --target=powerpc-apple-darwin6.1
>Description:
With no optimization, specifying a register vector variable will stomp on the temporary registers used by the vec_abs function, which actually generates 3 vector instructions.
>How-To-Repeat:
void VecAbsIsBroken (short *image)
/* gcc3.3 broken at -O0, works at -O1 and above, remove register keyword to fix */
{
short *p;
register vector signed short v;
p = image;
v = vec_ld (0, p);
v = vec_abs (v);
printf ("%p %hd: ", p, *p);
PrintShortVector (v); printf ("\n");
}
/*
_VecAbsIsBroken:
L_VecAbsIsBroken$stub:
mfspr r12,256
stw r12,-12(r1)
oris r12,r12,0xdfff
ori r12,r12,61440
mtspr 256,r12
mflr r0
stw r30,-8(r1)
stw r31,-4(r1)
stw r0,8(r1)
stwu r1,-96(r1)
mr r30,r1
bcl 20,31,L4$pb
L4$pb:
mflr r31
stw r3,120(r30)
lwz r0,120(r30)
stw r0,56(r30)
li r11,0
lwz r9,56(r30)
lvx v0,r11,r9
addi r9,r30,64
stvx v0,0,r9
addi r9,r30,64
lvx v1,0,r9 By loading v1 with the input to vec_abs, we doom it to fail
vspltisb v1,0 v1 should NOT be used as a temporary register here
vsubuhm v13,v1,v1 This just zeroed out v13, not good!
vmaxsh v0,v1,v13 So we end up with 0s!
addi r9,r30,64
stvx v0,0,r9
*/
>Fix:
Workaround: Use higher optimization levels. Still, without optimization the code should be generated correctly.
>Release-Note:
>Audit-Trail:
>Unformatted: