http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57830
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |jakub at gcc dot gnu.org
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The folding only folds the memcpy into
MEM[(char * {ref-all})lp] = MEM[(char * {ref-all})&l];
which is certainly desirable, as it improves optimizations, and at any point
can be expanded back to memcpy if that is desirable.
It is early SRA that turns that
l[1] = _12;
_14 = strlen (q_8);
l[2] = _14;
_16 = strlen (r_10);
...
MEM[(char * {ref-all})lp_32(D)] = MEM[(char * {ref-all})&l];
into the scalar stores and in the end actually increases the register pressure
when you don't have enough call clobbered registers. Note the testcase is
highlly artificial, and predicting whether the SRA is a win or not is very
hard.
If you look at how it is optimized with the strlen pass actually run (-Os
-foptimize-strlen, for -O2 it is enabled by default) you'll see that it is
actually a win, instead of storing constants into memory and then memcpying it
afterwards you store constants into memory at the end (with 4 exceptions I
think).
