Add support for combining GEPs across PHI nodes

Description

Add support for combining GEPs across PHI nodes

Currently LLVM will generally merge GEPs. This allows backends to use more
complex addressing modes. In some cases this is not happening because there
is PHI inbetween the two GEPs:

GEP1--\
      |-->PHI1-->GEP3
GEP2--/

This patch checks to see if GEP1 and GEP2 are similiar enough that they can be
cloned (GEP12) in GEP3's BB, allowing GEP->GEP merging (GEP123):

GEP1--\                     --\                           --\
      |-->PHI1-->GEP3  ==>    |-->PHI2->GEP12->GEP3 == >    |-->PHI2->GEP123
GEP2--/                     --/                           --/

This also breaks certain use chains that are preventing GEP->GEP merges that the
the existing instcombine would merge otherwise.

Tests included.

Details

Committed
louisMay 29 2014, 1:29 PM
Parents
rL209842: Thread Safety Analysis: minor changes to TIL pretty-printing.
Branches
Unknown
Tags
Unknown