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limit the number of instructions per block examined by dead store elimination

Authored by inglorion on Aug 26 2016, 9:34 AM.

Description

limit the number of instructions per block examined by dead store elimination

Summary: Dead store elimination gets very expensive when large numbers of instructions need to be analyzed. This patch limits the number of instructions analyzed per store to the value of the memdep-block-scan-limit parameter (which defaults to 100). This resulted in no observed difference in performance of the generated code, and no change in the statistics for the dead store elimination pass, but improved compilation time on some files by more than an order of magnitude.

Reviewers: dexonsmith, bruno, george.burgess.iv, dberlin, reames, davidxl

Subscribers: davide, chandlerc, dberlin, davidxl, eraman, tejohnson, mbodart, llvm-commits

Differential Revision: https://reviews.llvm.org/D15537

llvm-svn: 279833