[PATCH] D86452: [LV] Fix scalar cost for tail predicated loops

[Dave Green via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGab97c9bdb747: [LV] Fix scalar cost for tail predicated loops (authored by dmgreen).

Changed prior to commit:
  https://reviews.llvm.org/D86452?vs=287391&id=311390#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D86452/new/

https://reviews.llvm.org/D86452

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
  llvm/test/Transforms/LoopVectorize/ARM/scalar-block-cost.ll


Index: llvm/test/Transforms/LoopVectorize/ARM/scalar-block-cost.ll
===================================================================
--- llvm/test/Transforms/LoopVectorize/ARM/scalar-block-cost.ll
+++ llvm/test/Transforms/LoopVectorize/ARM/scalar-block-cost.ll
@@ -15,7 +15,7 @@
 ; CHECK-COST-NEXT: LV: Found an estimated cost of 1 for VF 1 For instruction:   store i32 %add1, i32* %arrayidx2, align 4
 ; CHECK-COST-NEXT: LV: Found an estimated cost of 1 for VF 1 For instruction:   %exitcond.not = icmp eq i32 %add, %n
 ; CHECK-COST-NEXT: LV: Found an estimated cost of 0 for VF 1 For instruction:   br i1 %exitcond.not, label %exit.loopexit, label %for.body
-; CHECK-COST-NEXT: LV: Scalar loop costs: 2.
+; CHECK-COST-NEXT: LV: Scalar loop costs: 5.
 
 entry:
   %cmp8 = icmp sgt i32 %n, 0
Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -6483,9 +6483,10 @@
     // if-converted. This means that the block's instructions (aside from
     // stores and instructions that may divide by zero) will now be
     // unconditionally executed. For the scalar case, we may not always execute
-    // the predicated block. Thus, scale the block's cost by the probability of
-    // executing it.
-    if (VF.isScalar() && blockNeedsPredication(BB))
+    // the predicated block, if it is an if-else block. Thus, scale the block's
+    // cost by the probability of executing it. blockNeedsPredication from
+    // Legal is used so as to not include all blocks in tail folded loops.
+    if (VF.isScalar() && Legal->blockNeedsPredication(BB))
       BlockCost.first /= getReciprocalPredBlockProb();
 
     Cost.first += BlockCost.first;


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