[TTI] Use getCastInstrCost for getUserCost Exts

[samparker]

Summary

First query whether an implementation believes an instruction is free via getExtCost and otherwise return getCastInstrCost.

[samparker]

The better situation is in D78922.

llvm/include/llvm/Analysis/TargetTransformInfoImpl.h

     case Instruction::BitCast:
       // Check if the operation is free according to the datalayout.
       if (getCastInstrCost(Opcode, Ty, OpTy, I) == 0)
         return 0;
       return TargetTTI->getCastInstrCost(Opcode, Ty, OpTy, I);
     case Instruction::FPExt:
     case Instruction::SExt:
     case Instruction::ZExt:
-      if (TargetTTI->getExtCost(I, Operands.back()) == TTI::TCC_Free)
-        return TTI::TCC_Free;
-      break;
+      if (I && TargetTTI->getExtCost(I, Operands.back()) == 0)
+        return 0;
+      return TargetTTI->getCastInstrCost(Opcode, Ty, OpTy, I);
     }
     // By default, just classify everything as 'basic'.
     return TTI::TCC_Basic;
   }
 
   int getInstructionLatency(const Instruction *I) {
     SmallVector<const Value *, 4> Operands(I->value_op_begin(),
                                            I->value_op_end());

llvm/test/Analysis/CostModel/SystemZ/ext-of-icmp-cost.ll

 ; RUN: opt < %s -cost-model -cost-kind=code-size -analyze \
 ; RUN:   -mtriple=s390x-unknown-linux -mcpu=z13  | FileCheck %s
 ;
 ; Check that getUserCost() does not return TCC_Free for extensions of
 ; i1 returned from icmp.
 
 define i64 @fun1(i64 %v) {
 ; CHECK-LABEL: 'fun1'
 ; CHECK: Cost Model: Found an estimated cost of 1 for instruction:   %cmp = icmp eq i64 %v, 0
-; CHECK: Cost Model: Found an estimated cost of 1 for instruction:   %z = zext i1 %cmp to i64
+; CHECK: Cost Model: Found an estimated cost of 2 for instruction:   %z = zext i1 %cmp to i64
 ; CHECK: Cost Model: Found an estimated cost of 1 for instruction:   ret i64 %z
   %cmp = icmp eq i64 %v, 0
   %z = zext i1 %cmp to i64
   ret i64 %z
 }
 
 define i64 @fun2(i64 %v) {
 ; CHECK-LABEL: 'fun2'
 ; CHECK: Cost Model: Found an estimated cost of 1 for instruction:   %cmp = icmp eq i64 %v, 0
-; CHECK: Cost Model: Found an estimated cost of 1 for instruction:   %z = sext i1 %cmp to i64
+; CHECK: Cost Model: Found an estimated cost of 2 for instruction:   %z = sext i1 %cmp to i64
 ; CHECK: Cost Model: Found an estimated cost of 1 for instruction:   ret i64 %z
   %cmp = icmp eq i64 %v, 0
   %z = sext i1 %cmp to i64
   ret i64 %z
 }
 
 define double @fun3(i64 %v) {
 ; CHECK-LABEL: 'fun3'

 ; CHECK: Cost Model: Found an estimated cost of 1 for instruction:   ret double %z
   %cmp = icmp eq i64 %v, 0
   %z = sitofp i1 %cmp to double
   ret double %z
 }
 
 define i64 @fun5(i1 %v) {
 ; CHECK-LABEL: 'fun5'
-; CHECK: Cost Model: Found an estimated cost of 1 for instruction:   %z = zext i1 %v to i64
+; CHECK: Cost Model: Found an estimated cost of 2 for instruction:   %z = zext i1 %v to i64
 ; CHECK: Cost Model: Found an estimated cost of 1 for instruction:   ret i64 %z
   %z = zext i1 %v to i64
   ret i64 %z
 }