http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56999
Bug #: 56999
Summary: [4.8/4.9 Regression] LRA caused miscompilation of
xulrunner
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: rtl-optimization
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
With -fpic -O2 -m32 -march=i686 -mtune=atom the following testcase is
miscompiled with LRA (but, I don't have a runtime testcase, just eyeball
assembly right now). The bad code is:
movl 24(%esp), %eax
addl $12, %eax
movl %eax, 24(%esp)
addl $8, %eax
testb %cl, %cl
movl 24(%esp), %ecx
cmovne %ecx, %eax
movl %eax, 24(%esp)
while reload has:
movl %ecx, %eax
addl $8, %ecx
addl $12, %eax
cmpb $0, 23(%esp)
cmove %ecx, %eax
instead. So, reload performs the intentional ptr + (flag ? 12 : 8) while
the LRA code performs ptr + (flag ? 12 : 20) instead. The source code related
to this is barriers ? &mJITInfo->jitHandleCtorBarriered :
&mJITInfo->jitHandleCtor where offsetof (JITScriptSet, jitHandleCtorBarriered)
== 12 and offsetof (JITScriptSet, jitHandleCtor) is 8, there is no field at
offset 20.
