[PATCH] D15995: [LTO] Add a run of LoopUnroll

[James Molloy via llvm-commits]

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Loop trip counts can often be resolved during LTO. We should obviously be unrolling small loops once those trip counts have been resolved, but we weren't.

This causes no change in a -flto run of the test-suite for me, but the nature of fully unrolling loops is that when they trigger, they cause massive changes in runtime. We observe this on third party test suites.

Repository:
  rL LLVM

http://reviews.llvm.org/D15995

Files:
  lib/Transforms/IPO/PassManagerBuilder.cpp

Index: lib/Transforms/IPO/PassManagerBuilder.cpp
===================================================================
--- lib/Transforms/IPO/PassManagerBuilder.cpp
+++ lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -570,6 +570,8 @@
   // More loops are countable; try to optimize them.
   PM.add(createIndVarSimplifyPass());
   PM.add(createLoopDeletionPass());
+  if (!DisableUnrollLoops)
+    PM.add(createSimpleLoopUnrollPass());   // Unroll small loops
   if (EnableLoopInterchange)
     PM.add(createLoopInterchangePass());
 


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