[ConstHoisting] choose to hoist when frequency is the same.

The patch is to adjust the strategy of frequency based consthoisting:
Previously when the candidate block has the same frequency with the existing
blocks containing a const, it will not hoist the const to the candidate block.
For that case, now we change the strategy to hoist the const if only existing
blocks have more than one block member. This is helpful for reducing code size.

Differential Revision: https://reviews.llvm.org/D35084

llvm-svn: 307328

1 files changed, 11 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp b/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
index a49c9b68c97..5f4a785b627 100644
--- a/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
@@ -231,7 +231,8 @@ static void findBestInsertionSet(DominatorTree &DT, BlockFrequencyInfo &BFI,
     // Return the optimal insert points in BBs.
     if (Node == Entry) {
       BBs.clear();
-      if (InsertPtsFreq > BFI.getBlockFreq(Node))
+      if (InsertPtsFreq > BFI.getBlockFreq(Node) ||
+          (InsertPtsFreq == BFI.getBlockFreq(Node) && InsertPts.size() > 1))
         BBs.insert(Entry);
       else
         BBs.insert(InsertPts.begin(), InsertPts.end());
@@ -244,7 +245,15 @@ static void findBestInsertionSet(DominatorTree &DT, BlockFrequencyInfo &BFI,
     SmallPtrSet<BasicBlock *, 16> &ParentInsertPts = InsertPtsMap[Parent].first;
     BlockFrequency &ParentPtsFreq = InsertPtsMap[Parent].second;
     // Choose to insert in Node or in subtree of Node.
-    if (InsertPtsFreq > BFI.getBlockFreq(Node) || NodeInBBs) {
+    // Don't hoist to EHPad because we may not find a proper place to insert
+    // in EHPad.
+    // If the total frequency of InsertPts is the same as the frequency of the
+    // target Node, and InsertPts contains more than one nodes, choose hoisting
+    // to reduce code size.
+    if (NodeInBBs ||
+        (!Node->isEHPad() &&
+         (InsertPtsFreq > BFI.getBlockFreq(Node) ||
+          (InsertPtsFreq == BFI.getBlockFreq(Node) && InsertPts.size() > 1)))) {
       ParentInsertPts.insert(Node);
       ParentPtsFreq += BFI.getBlockFreq(Node);
     } else {