[llvm] r205264 - Move partial/runtime unrolling late in the pipeline

[Hal Finkel]

Author: hfinkel
Date: Mon Mar 31 18:23:51 2014
New Revision: 205264

URL: http://llvm.org/viewvc/llvm-project?rev=205264&view=rev
Log:
Move partial/runtime unrolling late in the pipeline

The generic (concatenation) loop unroller is currently placed early in the
standard optimization pipeline. This is a good place to perform full unrolling,
but not the right place to perform partial/runtime unrolling. However, most
targets don't enable partial/runtime unrolling, so this never mattered.

However, even some x86 cores benefit from partial/runtime unrolling of very
small loops, and follow-up commits will enable this. First, we need to move
partial/runtime unrolling late in the optimization pipeline (importantly, this
is after SLP and loop vectorization, as vectorization can drastically change
the size of a loop), while keeping the full unrolling where it is now. This
change does just that.

Modified:
    llvm/trunk/include/llvm/Transforms/Scalar.h
    llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
    llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
    llvm/trunk/test/Transforms/LoopVectorize/X86/already-vectorized.ll

Modified: llvm/trunk/include/llvm/Transforms/Scalar.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Scalar.h?rev=205264&r1=205263&r2=205264&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Transforms/Scalar.h (original)
+++ llvm/trunk/include/llvm/Transforms/Scalar.h Mon Mar 31 18:23:51 2014
@@ -142,6 +142,8 @@ Pass *createLoopInstSimplifyPass();
 //
 Pass *createLoopUnrollPass(int Threshold = -1, int Count = -1,
                            int AllowPartial = -1, int Runtime = -1);
+// Create an unrolling pass for full unrolling only.
+Pass *createSimpleLoopUnrollPass();
 
 //===----------------------------------------------------------------------===//
 //

Modified: llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp?rev=205264&r1=205263&r2=205264&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp Mon Mar 31 18:23:51 2014
@@ -195,7 +195,7 @@ void PassManagerBuilder::populateModuleP
   MPM.add(createLoopDeletionPass());          // Delete dead loops
 
   if (!DisableUnrollLoops)
-    MPM.add(createLoopUnrollPass());          // Unroll small loops
+    MPM.add(createSimpleLoopUnrollPass());    // Unroll small loops
   addExtensionsToPM(EP_LoopOptimizerEnd, MPM);
 
   if (OptLevel > 1)
@@ -247,6 +247,9 @@ void PassManagerBuilder::populateModuleP
   MPM.add(createInstructionCombiningPass());
   MPM.add(createCFGSimplificationPass());
 
+  if (!DisableUnrollLoops)
+    MPM.add(createLoopUnrollPass());    // Unroll small loops
+
   if (!DisableUnitAtATime) {
     // FIXME: We shouldn't bother with this anymore.
     MPM.add(createStripDeadPrototypesPass()); // Get rid of dead prototypes

Modified: llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp?rev=205264&r1=205263&r2=205264&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp Mon Mar 31 18:23:51 2014
@@ -125,6 +125,10 @@ Pass *llvm::createLoopUnrollPass(int Thr
   return new LoopUnroll(Threshold, Count, AllowPartial, Runtime);
 }
 
+Pass *llvm::createSimpleLoopUnrollPass() {
+  return llvm::createLoopUnrollPass(-1, -1, 0, 0);
+}
+
 /// ApproximateLoopSize - Approximate the size of the loop.
 static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls,
                                     bool &NotDuplicatable,

Modified: llvm/trunk/test/Transforms/LoopVectorize/X86/already-vectorized.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/X86/already-vectorized.ll?rev=205264&r1=205263&r2=205264&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/X86/already-vectorized.ll (original)
+++ llvm/trunk/test/Transforms/LoopVectorize/X86/already-vectorized.ll Mon Mar 31 18:23:51 2014
@@ -1,4 +1,4 @@
-; RUN: opt < %s -debug-only=loop-vectorize -O3 -S 2>&1 | FileCheck %s
+; RUN: opt < %s -disable-loop-unrolling -debug-only=loop-vectorize -O3 -S 2>&1 | FileCheck %s
 ; REQUIRES: asserts
 ; We want to make sure that we don't even try to vectorize loops again
 ; The vectorizer used to mark the un-vectorized loop only as already vectorized