[LoopUnrolling] Re-prioritize Peeling and Partial unrolling
Summary:
In current implementation the loop peeling happens after trip-count based partial unrolling and may
sometimes not happen at all due to it (for example, if trip count is known, but UP.Partial = false). This
is generally bad, the more than there are some situations where peeling is profitable even if the partial
unrolling is disabled.
This patch is a NFC which reorders peeling and partial unrolling application and prepares the code for
implementation of the said optimizations.
Patch by Max Kazantsev!
Reviewers: sanjoy, anna, reames, apilipenko, igor-laevsky, mkuper
Reviewed By: mkuper
Subscribers: mkuper, llvm-commits, mzolotukhin
Differential Revision: https://reviews.llvm.org/D30243
llvm-svn: 296897
diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index 95daf3b..6e5cee4 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -784,7 +784,15 @@
}
}
- // 4rd priority is partial unrolling.
+ // 4th priority is loop peeling
+ computePeelCount(L, LoopSize, UP, TripCount);
+ if (UP.PeelCount) {
+ UP.Runtime = false;
+ UP.Count = 1;
+ return ExplicitUnroll;
+ }
+
+ // 5th priority is partial unrolling.
// Try partial unroll only when TripCount could be staticaly calculated.
if (TripCount) {
UP.Partial |= ExplicitUnroll;
@@ -847,14 +855,6 @@
<< "Unable to fully unroll loop as directed by unroll(full) pragma "
"because loop has a runtime trip count.");
- // 5th priority is loop peeling
- computePeelCount(L, LoopSize, UP);
- if (UP.PeelCount) {
- UP.Runtime = false;
- UP.Count = 1;
- return ExplicitUnroll;
- }
-
// 6th priority is runtime unrolling.
// Don't unroll a runtime trip count loop when it is disabled.
if (HasRuntimeUnrollDisablePragma(L)) {
diff --git a/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp b/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp
index 3cb9e6e..0227f8a 100644
--- a/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp
@@ -61,7 +61,8 @@
// Return the number of iterations we want to peel off.
void llvm::computePeelCount(Loop *L, unsigned LoopSize,
- TargetTransformInfo::UnrollingPreferences &UP) {
+ TargetTransformInfo::UnrollingPreferences &UP,
+ unsigned &TripCount) {
UP.PeelCount = 0;
if (!canPeel(L))
return;
@@ -70,6 +71,11 @@
if (!L->empty())
return;
+ // Bail if we know the statically calculated trip count.
+ // In this case we rather prefer partial unrolling.
+ if (TripCount)
+ return;
+
// If the user provided a peel count, use that.
bool UserPeelCount = UnrollForcePeelCount.getNumOccurrences() > 0;
if (UserPeelCount) {