Add an interface to scale the frequencies of a set of blocks.
The scaling is done with reference to the the new frequency of a reference block.
Differential Revision: https://reviews.llvm.org/D28535
llvm-svn: 292507
diff --git a/llvm/lib/Analysis/BlockFrequencyInfo.cpp b/llvm/lib/Analysis/BlockFrequencyInfo.cpp
index 9c1c966..1c4e28f 100644
--- a/llvm/lib/Analysis/BlockFrequencyInfo.cpp
+++ b/llvm/lib/Analysis/BlockFrequencyInfo.cpp
@@ -180,6 +180,28 @@
BFI->setBlockFreq(BB, Freq);
}
+void BlockFrequencyInfo::setBlockFreqAndScale(
+ const BasicBlock *ReferenceBB, uint64_t Freq,
+ SmallPtrSetImpl<BasicBlock *> &BlocksToScale) {
+ assert(BFI && "Expected analysis to be available");
+ // Use 128 bits APInt to avoid overflow.
+ APInt NewFreq(128, Freq);
+ APInt OldFreq(128, BFI->getBlockFreq(ReferenceBB).getFrequency());
+ APInt BBFreq(128, 0);
+ for (auto *BB : BlocksToScale) {
+ BBFreq = BFI->getBlockFreq(BB).getFrequency();
+ // Multiply first by NewFreq and then divide by OldFreq
+ // to minimize loss of precision.
+ BBFreq *= NewFreq;
+ // udiv is an expensive operation in the general case. If this ends up being
+ // a hot spot, one of the options proposed in
+ // https://reviews.llvm.org/D28535#650071 could be used to avoid this.
+ BBFreq = BBFreq.udiv(OldFreq);
+ BFI->setBlockFreq(BB, BBFreq.getLimitedValue());
+ }
+ BFI->setBlockFreq(ReferenceBB, Freq);
+}
+
/// Pop up a ghostview window with the current block frequency propagation
/// rendered using dot.
void BlockFrequencyInfo::view() const {