[PATCH] D114646: [LV] Pass compare predicate to getCmpSelInstrCost.

[Sander de Smalen via Phabricator via llvm-commits]

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If the condition of a select is a compare, pass its predicate to
TTI::getCmpSelInstrCost to get a more accurate cost value instead
of passing BAD_ICMP_PREDICATE.

I noticed that the commit message from D90070 <https://reviews.llvm.org/D90070> had a comment about the
vectorized select predicate possibly being composed of other compares with
different predicate values, but I wasn't able to construct an example
where this was an actual issue. If this is an issue, I guess we could
add another check that the block isn't predicated for any reason.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D114646

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
  llvm/test/Transforms/LoopVectorize/AArch64/select-costs.ll


Index: llvm/test/Transforms/LoopVectorize/AArch64/select-costs.ll
===================================================================
--- llvm/test/Transforms/LoopVectorize/AArch64/select-costs.ll
+++ llvm/test/Transforms/LoopVectorize/AArch64/select-costs.ll
@@ -5,17 +5,17 @@
 target triple = "arm64-apple-ios5.0.0"
 
 define void @selects_1(i32* nocapture %dst, i32 %A, i32 %B, i32 %C, i32 %N) {
-; CHECK: LV: Found an estimated cost of 5 for VF 2 For instruction:   %cond = select i1 %cmp1, i32 10, i32 %and
-; CHECK: LV: Found an estimated cost of 5 for VF 2 For instruction:   %cond6 = select i1 %cmp2, i32 30, i32 %and
-; CHECK: LV: Found an estimated cost of 5 for VF 2 For instruction:   %cond11 = select i1 %cmp7, i32 %cond, i32 %cond6
+; CHECK: LV: Found an estimated cost of 1 for VF 2 For instruction:   %cond = select i1 %cmp1, i32 10, i32 %and
+; CHECK: LV: Found an estimated cost of 1 for VF 2 For instruction:   %cond6 = select i1 %cmp2, i32 30, i32 %and
+; CHECK: LV: Found an estimated cost of 1 for VF 2 For instruction:   %cond11 = select i1 %cmp7, i32 %cond, i32 %cond6
 
-; CHECK: LV: Found an estimated cost of 13 for VF 4 For instruction:   %cond = select i1 %cmp1, i32 10, i32 %and
-; CHECK: LV: Found an estimated cost of 13 for VF 4 For instruction:   %cond6 = select i1 %cmp2, i32 30, i32 %and
-; CHECK: LV: Found an estimated cost of 13 for VF 4 For instruction:   %cond11 = select i1 %cmp7, i32 %cond, i32 %cond6
+; CHECK: LV: Found an estimated cost of 1 for VF 4 For instruction:   %cond = select i1 %cmp1, i32 10, i32 %and
+; CHECK: LV: Found an estimated cost of 1 for VF 4 For instruction:   %cond6 = select i1 %cmp2, i32 30, i32 %and
+; CHECK: LV: Found an estimated cost of 1 for VF 4 For instruction:   %cond11 = select i1 %cmp7, i32 %cond, i32 %cond6
 
 ; CHECK-LABEL: define void @selects_1(
 ; CHECK:       vector.body:
-; CHECK:         select <2 x i1>
+; CHECK:         select <4 x i1>
 
 entry:
   %cmp26 = icmp sgt i32 %N, 0
Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -7938,8 +7938,12 @@
     Type *CondTy = SI->getCondition()->getType();
     if (!ScalarCond)
       CondTy = VectorType::get(CondTy, VF);
-    return TTI.getCmpSelInstrCost(I->getOpcode(), VectorTy, CondTy,
-                                  CmpInst::BAD_ICMP_PREDICATE, CostKind, I);
+
+    CmpInst::Predicate Pred = CmpInst::BAD_ICMP_PREDICATE;
+    if (auto *Cmp = dyn_cast<CmpInst>(SI->getCondition()))
+      Pred = Cmp->getPredicate();
+    return TTI.getCmpSelInstrCost(I->getOpcode(), VectorTy, CondTy, Pred,
+                                  CostKind, I);
   }
   case Instruction::ICmp:
   case Instruction::FCmp: {


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