From a3bdb086c7ebc1a21844059620f8728f56ce93b4 Mon Sep 17 00:00:00 2001
From: James Molloy <james.molloy@arm.com>
Date: Thu, 5 Nov 2015 08:40:19 +0000
Subject: [PATCH] [SimplifyCFG] Tweak heuristic for merging conditional stores

We were correctly skipping dbginfo intrinsics and terminators, but the initial bailout wasn't, causing it to bail out on almost any block.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252152 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/SimplifyCFG.cpp | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 0a0c4a1044a..b119d2df035 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2426,14 +2426,20 @@ static bool mergeConditionalStoreToAddress(BasicBlock *PTB, BasicBlock *PFB,
     // Heuristic: if the block can be if-converted/phi-folded and the
     // instructions inside are all cheap (arithmetic/GEPs), it's worthwhile to
     // thread this store.
-    if (BB->size() > PHINodeFoldingThreshold)
-      return false;
-    for (auto &I : *BB)
-      if (!isa<BinaryOperator>(I) && !isa<GetElementPtrInst>(I) &&
-          !isa<StoreInst>(I) && !isa<TerminatorInst>(I) &&
-          !isa<DbgInfoIntrinsic>(I) && !IsaBitcastOfPointerType(I))
+    unsigned N = 0;
+    for (auto &I : *BB) {
+      // Cheap instructions viable for folding.
+      if (isa<BinaryOperator>(I) || isa<GetElementPtrInst>(I) ||
+          isa<StoreInst>(I))
+        ++N;
+      // Free instructions.
+      else if (isa<TerminatorInst>(I) || isa<DbgInfoIntrinsic>(I) ||
+               IsaBitcastOfPointerType(I))
+        continue;
+      else
         return false;
-    return true;
+    }
+    return N <= PHINodeFoldingThreshold;
   };
 
   if (!MergeCondStoresAggressively && (!IsWorthwhile(PTB) ||
-- 
2.34.1