[RISCV][CostModel] Remove cost of cmp inst in cmp+select with SFB.

With ShortFowrardBranchOpt(SFB) or ConditionalMoveFusion, scalar
ICmp and scalar Select instructinos will lower to SELECT_CC
and lower to PseudoCCMOVGPR which will generate a conditional
branch instr and a move instr.
The cost of scalar (ICmp + Select) = (0 + Select instr cost).

Author: ElvisWang123

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp

@@ -1443,6 +1443,17 @@ InstructionCost RISCVTTIImpl::getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
     }
   }
 
+  // With ShortForwardBranchOpt or ConditionalMoveFusion, scalar icmp + select
+  // instructions will lower to SELECT_CC and lower to PseudoCCMOVGPR which will
+  // generate a conditional branch + mv. The cost of scalar (icmp + select) will
+  // be (0 + select instr cost).
+  if (ST->hasConditionalMoveFusion() && I && isa<ICmpInst>(I) &&
+      !ValTy->isVectorTy() && I->hasOneUser() &&
+      isa<SelectInst>(I->user_back()) &&
+      !I->user_back()->getType()->isVectorTy() &&
+      I->user_back()->getOperand(0) == I)
+    return 0;
+
   // TODO: Add cost for scalar type.
 
   return BaseT::getCmpSelInstrCost(Opcode, ValTy, CondTy, VecPred, CostKind, I);

llvm/test/Analysis/CostModel/RISCV/cmp-select.ll

@@ -1,13 +1,35 @@
 ; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
-; RUN: opt < %s -mtriple=riscv64  -passes="print<cost-model>" -cost-kind=throughput 2>&1 -disable-output | FileCheck %s --check-prefixes=CHECK
+; RUN: opt < %s -mtriple=riscv64 -mcpu=sifive-u74 -passes="print<cost-model>" -cost-kind=throughput 2>&1 -disable-output | FileCheck %s --check-prefixes=SFB64
+; RUN: opt < %s -mtriple=riscv64 -passes="print<cost-model>" -cost-kind=throughput 2>&1 -disable-output | FileCheck %s --check-prefixes=RV64
 
-define void @cmp-select() {
-; CHECK-LABEL: 'cmp-select'
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %cmp1 = icmp slt i64 0, 1
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %select1 = select i1 %cmp1, i32 5, i32 4
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
-;
-  %cmp1 = icmp slt i64 0, 1
-  %select1 = select i1 %cmp1, i32 5, i32 4
+define i64 @icmp-select(i64 %a, i64 %b) {
+; SFB64-LABEL: 'icmp-select'
+; SFB64-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %cmp1 = icmp slt i64 0, 1
+; SFB64-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %select1 = select i1 %cmp1, i32 5, i32 4
+; SFB64-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
+;
+; RV64-LABEL: 'icmp-select'
+; RV64-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %cmp1 = icmp slt i64 0, 1
+; RV64-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %select1 = select i1 %cmp1, i32 5, i32 4
+; RV64-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
+;
+  %cmp1 = icmp slt i64 %a, %b
+  %select1 = select i1 %cmp1, i64 %a, i64 %b
+  ret i64 %select1
+}
+
+define void @fcmp-select() {
+; SFB64-LABEL: 'fcmp-select'
+; SFB64-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %fcmp1 = fcmp ogt float 0.000000e+00, 1.000000e+00
+; SFB64-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %select1 = select i1 %fcmp1, i32 5, i32 4
+; SFB64-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
+;
+; RV64-LABEL: 'fcmp-select'
+; RV64-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %fcmp1 = fcmp ogt float 0.000000e+00, 1.000000e+00
+; RV64-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %select1 = select i1 %fcmp1, i32 5, i32 4
+; RV64-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
+;
+  %fcmp1 = fcmp ogt float 0.0, 1.0
+  %select1 = select i1 %fcmp1, i32 5, i32 4
   ret void
 }