[llvm-commits] Code hoisting in GVN

[Rotem, Nadav]

Hi,


Please review the attached patch.

This patch adds code hoisting to GVN.  Currently, SimplifyCFG has a simple code hoisting procedure which scans both THEN and ELSE blocks of the branch and hoists instructions from both sides if they are identical.  The problem is that this linear scan is unable to find common code.  The alternative is to perform an N*M scan of the instructions in both blocks and find duplicated instructions. This patch implements the quadratic scan in GVN and has a threshold on the number of instructions to scan.  It gives a modest 1.5% speedup to SciMark2::MonteCarlo.

Thanks,
Nadav
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