https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98563
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |10.3
Status|UNCONFIRMED |NEW
Target| |x86_64-*-* i?86-*-*
Keywords| |missed-optimization, openmp
Summary|regression: vectorization |[10/11 Regression]
|fails while it worked on |vectorization fails while
|gcc 9 and earlier |it worked on gcc 9 and
| |earlier
Priority|P3 |P2
CC| |jakub at gcc dot gnu.org
Blocks| |53947
Ever confirmed|0 |1
Last reconfirmed| |2021-01-07
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the issue is that GCC 9 was able to vectorize the loop while GCC 10 and
trunk are not but those vectorize the basic block (where there's only enough
data to use SSE).
> g++-10 t.C -march=skylake-avx512 -O3 -fopenmp-simd -fdump-tree-vect-details
> -S -fopt-info-vec
t.C:4:6: optimized: basic block part vectorized using 32 byte vectors
> g++-9 t.C -march=skylake-avx512 -O3 -fopenmp-simd -fdump-tree-vect-details -S
> -fopt-info-vec
t.C:8:26: optimized: loop vectorized using 32 byte vectors
the reason it fails is
Creating dr for REALPART_EXPR <D.49590[_13]._M_value>
analyze_innermost: t.C:4:6: missed: failed: evolution of offset is not affine.
base_address:
offset from base address:
constant offset from base address:
step:
base alignment: 0
base misalignment: 0
offset alignment: 0
step alignment: 0
base_object: D.49590
Access function 0: 0
Access function 1: 0
Access function 2: scev_not_known;
where this is
_13 = .GOMP_SIMD_LANE (simduid.0_12(D), 0);
REALPART_EXPR <D.49590[_13]._M_value> = _26;
IMAGPART_EXPR <D.49590[_13]._M_value> = _7;
_20 = REALPART_EXPR <MEM <struct complex[64]> [(const struct complex
&)&D.49590][_13]._M_value>;
I'm not sure why this is here with GCC 10+ but not GCC 9.
Jakub?
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations
