https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90267
Bug ID: 90267
Summary: [7.3 regression] wrong code generated wth -O2 as
missing data dependence base on memory
Product: gcc
Version: 7.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: zhongyunde at huawei dot com
Target Milestone: ---
Created attachment 46254
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46254&action=edit
a simple testcase
test case attached, and we can see the code in line 42 clear the memory point
with pstruDlTpcPara, so the value in the memory cross the line 42 is different.
39 TpcFingerNum[TpcIdex][0] = *(UINT32*)(void*)pstruDlTpcPara;
40 TpcFingerNum[TpcIdex][1] = pstruDlTpcPara->ucThreeSlotFngNum;
41
42 *(volatile UINT32*)(void*)pstruDlTpcPara = 0;
43
44 TpcFingerNum[TpcIdex][2] = *(UINT32*)(void*)pstruDlTpcPara;
45 TpcFingerNum[TpcIdex][3] = pstruDlTpcPara->ucThreeSlotFngNum;
base on the gcc 7.3, in the dumpfile test.c.037t.fre1, we can see the value _6
get before the operator of clear the memory. So it miss the data dependence
base on memory.
(Generated by cmd:../../GCC/gcc-730/binary/bin/gcc test.c -dAp -S -O2 -g3
-fdump-tree-all)
37 _4 = MEM[(struct STRU_CCH_DLTPC_PARA
*)&gastruDlTpcPara][_1].ucThreeSlotFngNum;
38 _6 = (unsigned int) _4;
39 TpcFingerNum[TpcIdex.0_2][1] = _6;
40 MEM[(volatile UINT32 *)pstruDlTpcPara_20] ={v} 0;
41 _8 = MEM[(UINT32 *)pstruDlTpcPara_20];
42 TpcFingerNum[TpcIdex.0_2][2] = _8;
43 TpcFingerNum[TpcIdex.0_2][3] = _6;
