[SimplifyCFG] don't sink common insts too soon (PR34603)

This should solve:
https://bugs.llvm.org/show_bug.cgi?id=34603
...by preventing SimplifyCFG from altering redundant instructions before early-cse has a chance to run.
It changes the default (canonical-forming) behavior of SimplifyCFG, so we're only doing the
sinking transform later in the optimization pipeline.

Differential Revision: https://reviews.llvm.org/D38566

llvm-svn: 320749

1 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
index b5d32a1ca57..3855e6245d8 100644
--- a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -630,6 +630,13 @@ void PassManagerBuilder::populateModulePassManager(
     addInstructionCombiningPass(MPM);
   }
 
+  // Cleanup after loop vectorization, etc. Simplification passes like CVP and
+  // GVN, loop transforms, and others have already run, so it's now better to
+  // convert to more optimized IR using more aggressive simplify CFG options.
+  // The extra sinking transform can create larger basic blocks, so do this
+  // before SLP vectorization.
+  MPM.add(createCFGSimplificationPass(1, true, true, false, true));
+
   if (RunSLPAfterLoopVectorization && SLPVectorize) {
     MPM.add(createSLPVectorizerPass()); // Vectorize parallel scalar chains.
     if (OptLevel > 1 && ExtraVectorizerPasses) {
@@ -638,9 +645,6 @@ void PassManagerBuilder::populateModulePassManager(
   }
 
   addExtensionsToPM(EP_Peephole, MPM);
-  // Switches to lookup tables and other transforms that may not be considered
-  // canonical by other IR passes.
-  MPM.add(createCFGSimplificationPass(1, true, true, false));
   addInstructionCombiningPass(MPM);
 
   if (!DisableUnrollLoops) {