[llvm-commits] [llvm] r113306 - /llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
Owen Anderson
resistor at mac.com
Tue Sep 7 16:15:30 PDT 2010
Author: resistor
Date: Tue Sep 7 18:15:30 2010
New Revision: 113306
URL: http://llvm.org/viewvc/llvm-project?rev=113306&view=rev
Log:
Add a separate unrolling threshold when the current function is being optimized for size.
The threshold value of 50 is arbitrary, and I chose it simply by analogy to the inlining thresholds, where
the baseline unrolling threshold is slightly smaller than the baseline inlining threshold. This could
undoubtedly use some tuning.
Modified:
llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp?rev=113306&r1=113305&r2=113306&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp Tue Sep 7 18:15:30 2010
@@ -49,6 +49,12 @@
/// that the loop unroll should be performed regardless of how much
/// code expansion would result.
static const unsigned NoThreshold = UINT_MAX;
+
+ // Threshold to use when optsize is specified (and there is no
+ // explicit -unroll-threshold).
+ static const unsigned OptSizeUnrollThreshold = 50;
+
+ unsigned CurrentThreshold;
bool runOnLoop(Loop *L, LPPassManager &LPM);
@@ -88,12 +94,22 @@
}
bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
+
LoopInfo *LI = &getAnalysis<LoopInfo>();
BasicBlock *Header = L->getHeader();
DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName()
<< "] Loop %" << Header->getName() << "\n");
(void)Header;
+
+ // Determine the current unrolling threshold. While this is normally set
+ // from UnrollThreshold, it is overridden to a smaller value if the current
+ // function is marked as optimize-for-size, and the unroll threshold was
+ // not user specified.
+ CurrentThreshold = UnrollThreshold;
+ if (Header->getParent()->hasFnAttr(Attribute::OptimizeForSize) &&
+ UnrollThreshold.getNumOccurrences() == 0)
+ CurrentThreshold = OptSizeUnrollThreshold;
// Find trip count
unsigned TripCount = L->getSmallConstantTripCount();
@@ -111,7 +127,7 @@
}
// Enforce the threshold.
- if (UnrollThreshold != NoThreshold) {
+ if (CurrentThreshold != NoThreshold) {
unsigned NumCalls;
unsigned LoopSize = ApproximateLoopSize(L, NumCalls);
DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n");
@@ -120,16 +136,16 @@
return false;
}
uint64_t Size = (uint64_t)LoopSize*Count;
- if (TripCount != 1 && Size > UnrollThreshold) {
+ if (TripCount != 1 && Size > CurrentThreshold) {
DEBUG(dbgs() << " Too large to fully unroll with count: " << Count
- << " because size: " << Size << ">" << UnrollThreshold << "\n");
+ << " because size: " << Size << ">" << CurrentThreshold << "\n");
if (!UnrollAllowPartial) {
DEBUG(dbgs() << " will not try to unroll partially because "
<< "-unroll-allow-partial not given\n");
return false;
}
// Reduce unroll count to be modulo of TripCount for partial unrolling
- Count = UnrollThreshold / LoopSize;
+ Count = CurrentThreshold / LoopSize;
while (Count != 0 && TripCount%Count != 0) {
Count--;
}
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