[PATCH] [msan] Run more optimization after MemorySanitizer pass

[Evgeniy Stepanov]

  I've reduced the CL to 6 optimization passes that really make a difference.

Hi kcc, chandlerc,

http://llvm-reviews.chandlerc.com/D189

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D189?vs=460&id=800#toc

Files:
  lib/CodeGen/BackendUtil.cpp

Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -184,6 +184,17 @@
   const CodeGenOptions &CGOpts = BuilderWrapper.getCGOpts();
   PM.add(createMemorySanitizerPass(CGOpts.SanitizeMemoryTrackOrigins,
                                    CGOpts.SanitizerBlacklistFile));
+
+  // Re-run some generic optimizations to simplify code generated by
+  // MemorySanitizer.
+  if (Builder.OptLevel > 0) {
+    PM.add(createEarlyCSEPass());
+    PM.add(createReassociatePass());
+    PM.add(createLICMPass());
+    PM.add(createGVNPass());
+    PM.add(createInstructionCombiningPass());
+    PM.add(createDeadStoreEliminationPass());
+  }
 }
 
 static void addThreadSanitizerPass(const PassManagerBuilder &Builder,
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