https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79333
Bug ID: 79333
Summary: FRE/PRE do not fold calls not-in-place and do not
allow folding to look at SSA defs during elimination
Product: gcc
Version: 7.0.1
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Target Milestone: ---
This for example shows as not folding memory builtins or not doing any complex
match.pd replacements for gcc.dg/tree-ssa/pr71078-3.c when match.h provides
for example
extern __inline __attribute__ ((__always_inline__)) __attribute__
((__gnu_inline__)) double __attribute__ ((__nothrow__ , __leaf__)) fabs (double
__x) { return __builtin_fabs (__x); }
as opposed to just a prototype. This results in
<bb 2> [100.00%]:
_1 = (double) f_3(D);
_8 = ABS_EXPR <_1>;
_2 = (double) f_3(D);
t2_5 = _2 / _8;
return t2_5;
which is not matched by the x / abs(x) -> copysign (1.0, x) pattern. You'd
expect FRE1 to do the CSE (it does) and elimination folding of the stmt
to turn op the __builtin_copysign but that doesn't happen because the fold_stmt
done by elimination doesn't allow SSA name following.
