[TTI] Add VecPred argument to getCmpSelInstrCost.

On some targets, like AArch64, vector selects can be efficiently lowered
if the vector condition is a compare with a supported predicate.

This patch adds a new argument to getCmpSelInstrCost, to indicate the
predicate of the feeding select condition. Note that it is not
sufficient to use the context instruction when querying the cost of a
vector select starting from a scalar one, because the condition of the
vector select could be composed of compares with different predicates.

This change greatly improves modeling the costs of certain
compare/select patterns on AArch64.

I am also planning on putting up patches to make use of the new argument in
SLPVectorizer & LV.

Reviewed By: dmgreen, RKSimon

Differential Revision: https://reviews.llvm.org/D90070

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index c4d90a4..a45b5cd 100644
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -2236,9 +2236,9 @@ template<typename T> static int costAndCollectOperands(
                         unsigned MinIdx, unsigned MaxIdx) {
     Operations.emplace_back(Opcode, MinIdx, MaxIdx);
     Type *OpType = S->getOperand(0)->getType();
-    return NumRequired *
-      TTI.getCmpSelInstrCost(Opcode, OpType,
-                             CmpInst::makeCmpResultType(OpType), CostKind);
+    return NumRequired * TTI.getCmpSelInstrCost(
+                             Opcode, OpType, CmpInst::makeCmpResultType(OpType),
+                             CmpInst::BAD_ICMP_PREDICATE, CostKind);
   };
 
   switch (S->getSCEVType()) {