[ConstantHoisting] Cache OptForSize.

[alinas]

CacheOptForSize to remove quadratic behavior.

For each constant analyzed, ConstantHoising calls shouldOptimizeForSize(F), which calls PSI.getTotalCallCount(F). PSI.getTotalCallCount(F) goes through all the instructions in all basic blocks, and checks if each is a call, to count them up.

This reduces llc time for a very large IR from ~10min to under 3min. Reproducer testcase is much too large to share.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Alina Sbirlea (alinas)

Changes

CacheOptForSize to remove quadratic behavior.

For each constant analyzed, ConstantHoising calls shouldOptimizeForSize(F), which calls PSI.getTotalCallCount(F). PSI.getTotalCallCount(F) goes through all the instructions in all basic blocks, and checks if each is a call, to count them up.

This reduces llc time for a very large IR from ~10min to under 3min. Reproducer testcase is much too large to share.

---

Full diff: https://github.com/llvm/llvm-project/pull/79170.diff

2 Files Affected:

• (modified) llvm/include/llvm/Transforms/Scalar/ConstantHoisting.h (+1)
• (modified) llvm/lib/Transforms/Scalar/ConstantHoisting.cpp (+4-3)

diff --git a/llvm/include/llvm/Transforms/Scalar/ConstantHoisting.h b/llvm/include/llvm/Transforms/Scalar/ConstantHoisting.h
index fa13ed73d506a44..a4d1653fdf4bc68 100644
--- a/llvm/include/llvm/Transforms/Scalar/ConstantHoisting.h
+++ b/llvm/include/llvm/Transforms/Scalar/ConstantHoisting.h
@@ -153,6 +153,7 @@ class ConstantHoistingPass : public PassInfoMixin<ConstantHoistingPass> {
   const DataLayout *DL;
   BasicBlock *Entry;
   ProfileSummaryInfo *PSI;
+  bool OptForSize;
 
   /// Keeps track of constant candidates found in the function.
   using ConstCandVecType = std::vector<consthoist::ConstantCandidate>;
diff --git a/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp b/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
index 9e40d94dd73c766..49f8761a1392326 100644
--- a/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
@@ -576,9 +576,6 @@ ConstantHoistingPass::maximizeConstantsInRange(ConstCandVecType::iterator S,
                                            ConstCandVecType::iterator &MaxCostItr) {
   unsigned NumUses = 0;
 
-  bool OptForSize = Entry->getParent()->hasOptSize() ||
-                    llvm::shouldOptimizeForSize(Entry->getParent(), PSI, BFI,
-                                                PGSOQueryType::IRPass);
   if (!OptForSize || std::distance(S,E) > 100) {
     for (auto ConstCand = S; ConstCand != E; ++ConstCand) {
       NumUses += ConstCand->Uses.size();
@@ -948,6 +945,10 @@ bool ConstantHoistingPass::runImpl(Function &Fn, TargetTransformInfo &TTI,
   this->Ctx = &Fn.getContext();
   this->Entry = &Entry;
   this->PSI = PSI;
+  this->OptForSize = Entry.getParent()->hasOptSize() ||
+                     llvm::shouldOptimizeForSize(Entry.getParent(), PSI, BFI,
+                                                 PGSOQueryType::IRPass);
+
   // Collect all constant candidates.
   collectConstantCandidates(Fn);
 

[alinas]

The change adding this was: https://reviews.llvm.org/D59514.