[LoopUnroll] Consider simplified operands while retrieving TTI instruction cost

Get more precise cost of instruction after LoopUnroll considering that
some operands of it can be simplified, e.g. induction variable will be
replaced by constant after full unrolling.

Author: skachkov-sc

llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp

@@ -443,7 +443,15 @@ static std::optional<EstimatedUnrollCost> analyzeLoopUnrollCost(
 
         // First accumulate the cost of this instruction.
         if (!Cost.IsFree) {
-          UnrolledCost += TTI.getInstructionCost(I, CostKind);
+          // Consider simplified operands in instruction cost.
+          SmallVector<Value *, 4> Operands;
+          transform(I->operands(), std::back_inserter(Operands),
+                    [&](Value *Op) {
+                      if (auto Res = SimplifiedValues.lookup(Op))
+                        return Res;
+                      return Op;
+                    });
+          UnrolledCost += TTI.getInstructionCost(I, Operands, CostKind);
           LLVM_DEBUG(dbgs() << "Adding cost of instruction (iteration "
                             << Iteration << "): ");
           LLVM_DEBUG(I->dump());

llvm/test/Transforms/LoopUnroll/RISCV/unroll-Os.ll

@@ -8,13 +8,13 @@ define void @foo(ptr %array, i32 %x) #0 {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
 ; CHECK:       for.body:
-; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[INDVARS_IV_NEXT:%.*]], [[FOR_BODY]] ]
-; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[ARRAY]], i64 [[INDVARS_IV]]
-; CHECK-NEXT:    store i32 [[X]], ptr [[ARRAYIDX]], align 4
-; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
-; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], 4
-; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[FOR_COND_CLEANUP:%.*]], label [[FOR_BODY]]
-; CHECK:       for.cond.cleanup:
+; CHECK-NEXT:    store i32 [[X]], ptr [[ARRAY]], align 4
+; CHECK-NEXT:    [[ARRAYIDX_1:%.*]] = getelementptr inbounds i32, ptr [[ARRAY]], i64 1
+; CHECK-NEXT:    store i32 [[X]], ptr [[ARRAYIDX_1]], align 4
+; CHECK-NEXT:    [[ARRAYIDX_2:%.*]] = getelementptr inbounds i32, ptr [[ARRAY]], i64 2
+; CHECK-NEXT:    store i32 [[X]], ptr [[ARRAYIDX_2]], align 4
+; CHECK-NEXT:    [[ARRAYIDX_3:%.*]] = getelementptr inbounds i32, ptr [[ARRAY]], i64 3
+; CHECK-NEXT:    store i32 [[X]], ptr [[ARRAYIDX_3]], align 4
 ; CHECK-NEXT:    ret void
 ;
 entry: