Constant merger patch to fix bug 17815 [Constant merging may illegally downgrade global alignment]

Chris Smowton chris at smowton.net
Tue Nov 5 06:12:38 PST 2013


Hi all,

I attach a patch to fix the constant merging pass, which can sometimes 
downgrade global alignment when one of those being merged has no 
specified alignment (i.e. getAlignment() == 0), causing apparent 
null-pointer segfaults that are actually x86 vector operation alignment 
faults.

See http://llvm.org/bugs/show_bug.cgi?id=17815 for a test case and full 
details. Patch is against 3.2 again I'm afraid due to time constraints, 
but it doesn't look as though constmerge has changed significantly since 
then.

Chris
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