[SLP] Fix for the min/max intrinsic cost.

[vporpo]

Summary

The min/max intrinsic cost is currently too low because in the cost calculation
we subtract the cost of the vector compare as we will not emit it.
For the cost of the vector compare we are currently passing BAD_ICMP_PREDICATE
which returns 3, the worst case cost.
I think we should be passing VecPred instead, since we know the predicates of
the compare instr.

I think this is related to commit b3b993a7ad817 which introduced the predicate
argument to getCmpSelInstrCost().
https://reviews.llvm.org/rGb3b993a7ad817c3c5801341fa78f34332900eb83

[ABataev]

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

5361–5362

This is not correct, the original code is correct. Need to check more carefully the cause and probably fix the comment.

[vporpo]

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

5361–5362

Yeah you are right. This should subtract the cost of the vectorized compares, not the vectorized selects. Let me look into it again.

[vporpo]

This looks more correct.

[vporpo]

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

5361–5362

I think the issue was the BAD_ICMP_PREDICATE. If I understand correctly we should be using VecPred here instead.

[ABataev]

LG

[vporpo]

Updated test.

[fhahn]

Lgtm thanks

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

case Instruction::Select: {
       if (IntrinsicAndUse.first != Intrinsic::not_intrinsic) {
         IntrinsicCostAttributes CostAttrs(IntrinsicAndUse.first, VecTy,
                                           {VecTy, VecTy});
         InstructionCost IntrinsicCost =
             TTI->getIntrinsicInstrCost(CostAttrs, CostKind);
         // If the selects are the only uses of the compares, they will be dead
         // and we can adjust the cost by removing their cost.
         if (IntrinsicAndUse.second)
-          IntrinsicCost -=
-              TTI->getCmpSelInstrCost(Instruction::ICmp, VecTy, MaskTy,
-                                      CmpInst::BAD_ICMP_PREDICATE, CostKind);
+          IntrinsicCost -= TTI->getCmpSelInstrCost(Instruction::ICmp, VecTy,
+                                                   MaskTy, VecPred, CostKind);
         VecCost = std::min(VecCost, IntrinsicCost);
       }
       LLVM_DEBUG(dumpTreeCosts(E, CommonCost, VecCost, ScalarCost));
       return CommonCost + VecCost - ScalarCost;
     }
     case Instruction::FNeg:
     case Instruction::Add:
     case Instruction::FAdd:

llvm/test/Transforms/SLPVectorizer/X86/arith-max-cost.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -slp-vectorizer -mcpu=corei7-avx -mtriple=x86_64-unknown-linux -S | FileCheck %s
 
 ; This test checks whether the cost of the vector max intrinsic is calculated
 ; correctly. A max vector intrinsic combines the select and icmp instructions.
 ; This maps to a single PMAX instruction in x86.
 define void @smax_intrinsic_cost(i64 %arg0, i64 %arg1) {
 ; CHECK-LABEL: @smax_intrinsic_cost(
-; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <2 x i64> poison, i64 [[ARG0:%.*]], i32 0
-; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <2 x i64> [[TMP1]], i64 [[ARG1:%.*]], i32 1
-; CHECK-NEXT:    [[TMP3:%.*]] = icmp sgt <2 x i64> [[TMP2]], <i64 123, i64 456>
-; CHECK-NEXT:    [[TMP4:%.*]] = select <2 x i1> [[TMP3]], <2 x i64> [[TMP2]], <2 x i64> <i64 123, i64 456>
-; CHECK-NEXT:    [[TMP5:%.*]] = extractelement <2 x i64> [[TMP4]], i32 0
-; CHECK-NEXT:    [[TMP6:%.*]] = extractelement <2 x i64> [[TMP4]], i32 1
-; CHECK-NEXT:    [[ROOT:%.*]] = icmp sle i64 [[TMP5]], [[TMP6]]
+; CHECK-NEXT:    [[ICMP0:%.*]] = icmp sgt i64 [[ARG0:%.*]], 123
+; CHECK-NEXT:    [[ICMP1:%.*]] = icmp sgt i64 [[ARG1:%.*]], 456
+; CHECK-NEXT:    [[SELECT0:%.*]] = select i1 [[ICMP0]], i64 [[ARG0]], i64 123
+; CHECK-NEXT:    [[SELECT1:%.*]] = select i1 [[ICMP1]], i64 [[ARG1]], i64 456
+; CHECK-NEXT:    [[ROOT:%.*]] = icmp sle i64 [[SELECT0]], [[SELECT1]]
 ; CHECK-NEXT:    ret void
 ;
   %icmp0 = icmp sgt i64 %arg0, 123
   %icmp1 = icmp sgt i64 %arg1, 456
   %select0 = select i1 %icmp0, i64 %arg0, i64 123
   %select1 = select i1 %icmp1, i64 %arg1, i64 456
   %root = icmp sle i64 %select0, %select1
   ret void