[Bug tree-optimization/57742] memset(malloc(n),0,n) -> calloc(n,1)
glisse at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Sun Feb 23 18:46:00 GMT 2014
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57742
Marc Glisse <glisse at gcc dot gnu.org> changed:
What |Removed |Added
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Attachment #30981|0 |1
is obsolete| |
Attachment #31003|0 |1
is obsolete| |
--- Comment #14 from Marc Glisse <glisse at gcc dot gnu.org> ---
Created attachment 32204
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32204&action=edit
New patch
This seems to work. It also handles the fortran example from comment #3. With a
comment before the new function and a testcase, it will be good to go to
gcc-patches.
Side note: at -O3, if I provide an inline version of operator new (see PR
59894), it handles std::vector<int>(n). However, I had to provide a simple one
(call malloc, if null throw). The one in libsupc++ is way too complicated (2
calls to malloc), and if I refactor it slightly so "malloc" only appears once,
I end up with the following. The edge probabilities are strange (malloc fails
in 95% of cases?), but mostly we have a PHI node with a single argument which
hides the fact that the variables are the same. It is far from the first time I
notice this, is there a real reason to keep those unary PHIs, or should we
optimize them more aggressively?
p_24 = mallocD.1405 (sz_20);
if (p_24 == 0B)
goto <bb 7>;
else
goto <bb 11>;
;; succ: 7 [95.5%] (TRUE_VALUE,EXECUTABLE)
;; 11 [4.5%] (FALSE_VALUE,EXECUTABLE)
;; basic block 11, loop depth 0, count 0, freq 349, maybe hot
;; prev block 10, next block 12, flags: (NEW, REACHABLE)
;; pred: 10 [4.5%] (FALSE_VALUE,EXECUTABLE)
# PT = { D.16587 } (escaped heap)
# ALIGN = 8, MISALIGN = 0
# p_41 = PHI <p_24(10)>
# .MEM_42 = VDEF <.MEM_34>
MEM[(struct _Vector_baseD.14156 *)p_2(D)]._M_implD.15030._M_startD.15032 =
p_41;
# PT = { D.16587 } (escaped heap)
# ALIGN = 4, MISALIGN = 0
_19 = p_41 + sz_20;
# .MEM_44 = VDEF <.MEM_42>
MEM[(struct _Vector_baseD.14156
*)p_2(D)]._M_implD.15030._M_end_of_storageD.15034 = _19;
# .MEM_8 = VDEF <.MEM_44>
# USE = anything
# CLB = anything
memsetD.1000 (p_41, 0, sz_20);
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