https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72772
Bug ID: 72772
Summary: Missed SCEV after pass reordering@236440
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: amker at gcc dot gnu.org
Target Milestone: ---
For below case
int foo (int flag, char *a)
{
short i, j;
short l = 0;
if (flag == 1)
l = 3;
for (i = 0; i < 4; i++)
{
for (j = l - 1; j > 0; j--)
a[j] = a[j - 1];
a[0] = i;
}
}
GCC can't recognize &a[j]/&a[j-1] as SCEVs after pass reordering @commit:
commit 410372fef14173261ce8e547db98eafb3174921f
Author: rguenth <rguenth@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Thu May 19 07:39:52 2016 +0000
2016-05-19 Richard Biener <rguent...@suse.de>
PR tree-optimization/70729
* passes.def: Move LIM pass before PRE. Remove no longer
required copyprop and move first DCE out of the loop pipeline.
* gcc.dg/autopar/outer-6.c: Adjust to avoid redundant store.
* gcc.dg/graphite/scop-18.c: Likewise.
* gcc.dg/pr41783.c: Disable LIM.
* gcc.dg/tree-ssa/loadpre10.c: Likewise.
* gcc.dg/tree-ssa/loadpre23.c: Likewise.
* gcc.dg/tree-ssa/loadpre24.c: Likewise.
* gcc.dg/tree-ssa/loadpre25.c: Likewise.
* gcc.dg/tree-ssa/loadpre4.c: Likewise.
* gcc.dg/tree-ssa/loadpre8.c: Likewise.
* gcc.dg/tree-ssa/ssa-pre-16.c: Likewise.
* gcc.dg/tree-ssa/ssa-pre-18.c: Likewise.
* gcc.dg/tree-ssa/ssa-pre-20.c: Likewise.
* gcc.dg/tree-ssa/ssa-pre-3.c: Likewise.
* gfortran.dg/pr42108.f90: Likewise.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@236440
138bc75d-0d04-0410-961f-82ee72b054a4
This is because of changed IR, from:
Loop_guard:
if (prephitmp_41 > 0)
goto <bb 8>;
else
goto <bb 6>;
Preheader:
<bb 8>:
Loop:
<bb 9>:
# j_29 = PHI <prephitmp_41(8), j_23(11)>
_3 = (sizetype) j_29;
_4 = a_21(D) + _3;
_5 = _3 + 18446744073709551615;
_6 = a_21(D) + _5;
_7 = *_6;
*_4 = _7;
j.2_8 = (unsigned short) j_29;
_9 = j.2_8 + 65535;
j_23 = (short int) _9;
if (j_23 > 0)
goto <bb 11>;
else
goto <bb 10>;
Latch:
<bb 11>:
goto <bb 9>;
To:
Loop_guard:
if (prephitmp_43 > 0)
goto <bb 6>;
else
goto <bb 10>;
Preheader:
<bb 6>:
# j_16 = PHI <prephitmp_43(5)>
Loop:
<bb 7>:
# j_29 = PHI <j_16(6), j_23(8)>
_3 = (sizetype) j_29;
_4 = a_21(D) + _3;
_5 = _3 + 18446744073709551615;
_6 = a_21(D) + _5;
_7 = *_6;
*_4 = _7;
j.2_8 = (unsigned short) j_29;
_9 = j.2_8 + 65535;
j_23 = (short int) _9;
if (j_23 > 0)
goto <bb 8>;
else
goto <bb 9>;
Latch:
<bb 8>:
goto <bb 7>;
Specifically, simplif_using_initial_conditions failed in this case because it
missed expanding simple operations in single-arg PHI in preheader.
