[CostModel][X86] X86TTIImpl::getCmpSelInstrCost - try to use Predicat…

…e argument directly first (PR48337)

There's still a lot of cases where getCmpSelInstrCost fails to specify a predicate, once those are in place we should be able to remove the fallback to the Instruction argument entirely.

llvm/lib/Target/X86/X86TargetTransformInfo.cpp

@@ -2420,13 +2420,21 @@ InstructionCost X86TTIImpl::getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
   assert(ISD && "Invalid opcode");
 
   unsigned ExtraCost = 0;
-  if (I && (Opcode == Instruction::ICmp || Opcode == Instruction::FCmp)) {
+  if (Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) {
     // Some vector comparison predicates cost extra instructions.
+    // TODO: Should we invert this and assume worst case cmp costs
+    // and reduce for particular predicates?
     if (MTy.isVector() &&
         !((ST->hasXOP() && (!ST->hasAVX2() || MTy.is128BitVector())) ||
           (ST->hasAVX512() && 32 <= MTy.getScalarSizeInBits()) ||
           ST->hasBWI())) {
-      switch (cast<CmpInst>(I)->getPredicate()) {
+      // Fallback to I if a specific predicate wasn't specified.
+      CmpInst::Predicate Pred = VecPred;
+      if (I && (Pred == CmpInst::BAD_ICMP_PREDICATE ||
+                Pred == CmpInst::BAD_FCMP_PREDICATE))
+        Pred = cast<CmpInst>(I)->getPredicate();
+
+      switch (Pred) {
       case CmpInst::Predicate::ICMP_NE:
         // xor(cmpeq(x,y),-1)
         ExtraCost = 1;