http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57579
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Federico Carminati from comment #0)
> Good evening,
> all my apologises if this is a stupid question, however I have a terribly
> simple loop
>
>
> include <math.h>
>
> typedef struct
> {
> double x,y,z;
> double dummy;
> } P;
>
>
> void foo(const P * __restrict__ points, double * __restrict__ d)
> {
> for(int i=0;i<100;++i) {
> d[i]=points[i].x*points[i].x*points[i].x*points[i].x+
> points[i].y*points[i].y*points[i].y+
> points[i].z*points[i].z*points[i].z;
> }
> }
>
> if I compile with
>
> /opt/gcc-4.8.1/bin/g++ -c -std=c++0x -O3 -msse4.1 -Wall -Wstrict-aliasing=2
> -ftree-vectorizer-verbose=2
>
> I obtain the diagnostic at the bottom of the page. Is there a place where I
> can find an explanation for the g++ vectorizer diagnostic messages? I
> frankly do not understand what it is talking about and google does not seem
> to be willing to help me this time. Any help in deciphering these messages
> would be greatly appreciated. Thanks and sorry for the bother
>
> Analyzing loop at testvec1.cxx:12
>
> testvec1.cxx:12: note: Data access with gaps requires scalar epilogue loop
> testvec1.cxx:12: note: vector alignment may not be reachable
> testvec1.cxx:12: note: virtual phi. skip.
> testvec1.cxx:12: note: not ssa-name.
> testvec1.cxx:12: note: use not simple.
> testvec1.cxx:12: note: not ssa-name.
> testvec1.cxx:12: note: use not simple.
> testvec1.cxx:12: note: no array mode for V2DF[4]
> testvec1.cxx:12: note: not ssa-name.
> testvec1.cxx:12: note: use not simple.
> testvec1.cxx:12: note: not ssa-name.
> testvec1.cxx:12: note: use not simple.
> testvec1.cxx:12: note: no array mode for V2DF[4]
> testvec1.cxx:12: note: not ssa-name.
> testvec1.cxx:12: note: use not simple.
> testvec1.cxx:12: note: not ssa-name.
> testvec1.cxx:12: note: use not simple.
> testvec1.cxx:12: note: no array mode for V2DF[4]
>
> Vectorizing loop at testvec1.cxx:12
^^^^
the loop is vectorized.
> testvec1.cxx:12: note: virtual phi. skip.
> testvec1.cxx:12: note: no array mode for V2DF[4]
> testvec1.cxx:12: note: no array mode for V2DF[4]
> testvec1.cxx:12: note: no array mode for V2DF[4]
> testvec1.cxx:10: note: vectorized 1 loops in function.
>
> testvec1.cxx:10: note: not vectorized: not enough data-refs in basic block.
>
> testvec1.cxx:13: note: not vectorized: no vectype for stmt: vect_var_.10_29
> = MEM[(const struct P *)vect_ppoints.6_31];
> scalar_type: const vector(2) double
> testvec1.cxx:13: note: Failed to SLP the basic block.
> testvec1.cxx:13: note: not vectorized: failed to find SLP opportunities in
> basic block.
>
> testvec1.cxx:13: note: Build SLP failed: grouped loads have gaps _59 =
> _60->x;
>
> testvec1.cxx:13: note: Failed to SLP the basic block.
> testvec1.cxx:13: note: not vectorized: failed to find SLP opportunities in
> basic block.
>
> testvec1.cxx:10: note: not vectorized: not enough data-refs in basic block.
the rest of the "complaints" are from basic-block vectorization trying to
vectorize the loop body again. Which of course fails, it is already
vectorized.
