Re: [PATCH] Fix PR77916

[Markus Trippelsdorf <markus at trippelsdorf dot de>]

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.

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




-- 
Markus