On Tue, 2016-10-18 at 05:13 +0200, Markus Trippelsdorf wrote:
> On 2016.10.17 at 17:23 -0500, Bill Schmidt wrote:
> > Hi,
> >
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77916 identifies a situation
> > where SLSR will ICE when exposed to a cast from integer to pointer. This
> > is because we try to convert a PLUS_EXPR with an addend of -1 * S into a
> > MINUS_EXPR with a subtrahend of S, but the base operand is unexpectedly
> > of pointer type. This patch recognizes when pointer arithmetic is taking
> > place and ensures that we use a POINTER_PLUS_EXPR at all such times. In
> > the case of the PR, this occurs in the logic where the stride S is a known
> > constant value, but the same problem could occur when it is an SSA_NAME
> > without known value. Both possibilities are handled here.
> >
> > Fixing the code to ensure that the unknown stride case always uses an
> > initializer for a negative increment allows us to remove the stopgap fix
> > added for PR77937 as well.
> >
> > Bootstrapped and tested on powerpc64le-unknown-linux-gnu with no
> > regressions, committed.
>
> Perhaps you should consider building ffmpeg with -O3 -march=amdfam10 on
> X86_64 before committing these patches, because you broke it for the
> third time in the last couple of days.
Sorry, sorry. I did intend to build another stage1 cross and try this,
but it just slipped my mind. Looks like I'll need to put the stopgap
fix back in. I'll do that shortly.
Meantime, -fno-slsr is a workaround. If I have trouble building ffmpeg
with a cross, I'll check with you on testing a future patch.
Bill
>
> markus@x4 ffmpeg % cat h264dsp.i
> extern int fn2(int);
> extern int fn3(int);
> int a, b, c;
> void fn1(long p1) {
> char *d;
> for (;; d += p1) {
> d[0] = fn2(1 >> c >> 1);
> fn2(c >> a);
> d[1] = fn3(d[1]) >> 1;
> d[6] = fn3(d[6] * b + 1) >> 1;
> d[7] = fn3(d[7] * b + 1) >> 1;
> d[8] = fn3(d[8] * b + 1) >> 1;
> }
> }
>
> markus@x4 ffmpeg % gcc -O3 -march=amdfam10 -c h264dsp.i
> h264dsp.i: In function ‘fn1’:
> h264dsp.i:4:6: internal compiler error: in replace_one_candidate, at
> gimple-ssa-strength-reduction.c:3375
> void fn1(long p1) {
> ^~~
> 0x12773a9 replace_one_candidate
> ../../gcc/gcc/gimple-ssa-strength-reduction.c:3375
> 0x127af77 replace_profitable_candidates
> ../../gcc/gcc/gimple-ssa-strength-reduction.c:3486
> 0x127aeeb replace_profitable_candidates
> ../../gcc/gcc/gimple-ssa-strength-reduction.c:3495
> 0x127f3ee analyze_candidates_and_replace
> ../../gcc/gcc/gimple-ssa-strength-reduction.c:3574
> 0x127f3ee execute
> ../../gcc/gcc/gimple-ssa-strength-reduction.c:3648
>
>
>
>
