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Move partial/runtime unrolling late in the pipeline

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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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205264 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel 2014-03-31 23:23:51 +00:00
parent 3021734700
commit 6bbb01bbf8
4 changed files with 11 additions and 2 deletions
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2
include/llvm/Transforms/Scalar.h
View File

@ -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();
//===----------------------------------------------------------------------===//
//

5
lib/Transforms/IPO/PassManagerBuilder.cpp
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@ -195,7 +195,7 @@ void PassManagerBuilder::populateModulePassManager(PassManagerBase &MPM) {
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::populateModulePassManager(PassManagerBase &MPM) {
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

4
lib/Transforms/Scalar/LoopUnrollPass.cpp
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@ -125,6 +125,10 @@ Pass *llvm::createLoopUnrollPass(int Threshold, int Count, int AllowPartial,
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,

2
test/Transforms/LoopVectorize/X86/already-vectorized.ll
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@ -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