remove the InstructionSimplifierPass immediately after InstructionCombiningPass

[wmi]

Summary

InstructionCombiningPass was added after LoopUnrollPass in r237395. Because InstructionCombiningPass is strictly more powerful than InstructionSimplifierPass, remove the unnecessary InstructionSimplifierPass.

[majnemer]

LGTM

llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp

void PassManagerBuilder::populateModulePassManager(
   MPM.add(createInstructionCombiningPass());
 
   if (!DisableUnrollLoops) {
     MPM.add(createLoopUnrollPass());    // Unroll small loops
 
     // LoopUnroll may generate some redundency to cleanup.
     MPM.add(createInstructionCombiningPass());
 
-    // This is a barrier pass to avoid combine LICM pass and loop unroll pass
-    // within same loop pass manager.
-    MPM.add(createInstructionSimplifierPass());
-
     // Runtime unrolling will introduce runtime check in loop prologue. If the
     // unrolled loop is a inner loop, then the prologue will be inside the
     // outer loop. LICM pass can help to promote the runtime check out if the
     // checked value is loop invariant.
     MPM.add(createLICMPass());
   }
 
   // After vectorization and unrolling, assume intrinsics may tell us more