[InstCombine] Fixed bug introduced in r282237

The index of the new insertelement instruction was evaluated in the
wrong way, it was considered as the index of the inserted value instead
of index of the position, where the value should be inserted.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@282401 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

@@ -1048,8 +1048,8 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
     if (TmpV) { I->setOperand(1, TmpV); MadeChange = true; }
 
     bool NewUndefElts = false;
-    unsigned LHSIdx = -1u;
-    unsigned RHSIdx = -1u;
+    unsigned LHSIdx = -1u, LHSValIdx = -1u;
+    unsigned RHSIdx = -1u, RHSValIdx = -1u;
     bool LHSUniform = true;
     bool RHSUniform = true;
     for (unsigned i = 0; i < VWidth; i++) {
@@ -1064,15 +1064,17 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
           NewUndefElts = true;
           UndefElts.setBit(i);
         } else {
-          LHSIdx = LHSIdx == -1u ? MaskVal : LHSVWidth;
+          LHSIdx = LHSIdx == -1u ? i : LHSVWidth;
+          LHSValIdx = LHSValIdx == -1u ? MaskVal : LHSVWidth;
           LHSUniform = LHSUniform && (MaskVal == i);
         }
       } else {
         if (RHSUndefElts[MaskVal - LHSVWidth]) {
           NewUndefElts = true;
           UndefElts.setBit(i);
         } else {
-          RHSIdx = RHSIdx == -1u ? MaskVal - LHSVWidth : LHSVWidth;
+          RHSIdx = RHSIdx == -1u ? i : LHSVWidth;
+          RHSValIdx = RHSValIdx == -1u ? MaskVal - LHSVWidth : LHSVWidth;
           RHSUniform = RHSUniform && (MaskVal - LHSVWidth == i);
         }
       }
@@ -1091,14 +1093,14 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
       if (LHSIdx < LHSVWidth && RHSUniform) {
         if (auto *CV = dyn_cast<ConstantVector>(Shuffle->getOperand(0))) {
           Op = Shuffle->getOperand(1);
-          Value = CV->getOperand(LHSIdx);
+          Value = CV->getOperand(LHSValIdx);
           Idx = LHSIdx;
         }
       }
       if (RHSIdx < LHSVWidth && LHSUniform) {
         if (auto *CV = dyn_cast<ConstantVector>(Shuffle->getOperand(1))) {
           Op = Shuffle->getOperand(0);
-          Value = CV->getOperand(RHSIdx);
+          Value = CV->getOperand(RHSValIdx);
           Idx = RHSIdx;
         }
       }

test/Transforms/InstCombine/vec_demanded_elts.ll

@@ -212,6 +212,15 @@ define <2 x double> @test_fpext(float %f) {
   ret <2 x double> %ret
 }
 
+define <4 x double> @test_shuffle(<4 x double> %f) {
+; CHECK-LABEL: @test_shuffle(
+; CHECK-NEXT:    [[RET1:%.*]] = insertelement <4 x double> %f, double 1.000000e+00, i32 3
+; CHECK-NEXT:    ret <4 x double> [[RET1]]
+;
+  %ret = shufflevector <4 x double> %f, <4 x double> <double undef, double 1.0, double undef, double undef>, <4 x i32> <i32 0, i32 1, i32 2, i32 5>
+  ret <4 x double> %ret
+}
+
 define <4 x float> @test_select(float %f, float %g) {
 ; CHECK-LABEL: @test_select(
 ; CHECK-NEXT:    [[A0:%.*]] = insertelement <4 x float> undef, float %f, i32 0