[PATCH] D13064: Add CFG Simplification pass after Loop Unswitching.

Michael Zolotukhin via llvm-commits llvm-commits at lists.llvm.org
Tue Sep 22 12:11:17 PDT 2015

mzolotukhin created this revision.
mzolotukhin added reviewers: chandlerc, hfinkel.
mzolotukhin added a subscriber: llvm-commits.

Loop unswitching produces conditional branches with constant condition,
and it's beneficial for later passes to clean this up with simplify-cfg.
We do this after the second invocation of loop-unswitch, but not after
the first one. Not doing so might cause problem for passes like
LoopUnroll, whose estimate of loop body size would be less accurate.



Index: lib/Transforms/IPO/PassManagerBuilder.cpp
--- lib/Transforms/IPO/PassManagerBuilder.cpp
+++ lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -260,6 +260,7 @@
   MPM.add(createLoopRotatePass(SizeLevel == 2 ? 0 : -1));
   MPM.add(createLICMPass());                  // Hoist loop invariants
   MPM.add(createLoopUnswitchPass(SizeLevel || OptLevel < 3));
+  MPM.add(createCFGSimplificationPass());
   MPM.add(createIndVarSimplifyPass());        // Canonicalize indvars
   MPM.add(createLoopIdiomPass());             // Recognize idioms like memset.

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