[SLP]Use revectorized value for extracts from buildvector, beeing

vectorized.

If the insertelement instruction is vectorized, and the extractelement
instruction from such insertelement also vectorized as part of the same
tree, need to extract from the corresponding for insertelement vectorized value rather than original insertelement instruction.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -11139,6 +11139,8 @@ Value *BoUpSLP::vectorizeTree(TreeEntry *E, bool PostponedPHIs) {
 
     case Instruction::ExtractElement: {
       Value *V = E->getSingleOperand(0);
+      if (const TreeEntry *TE = getTreeEntry(V))
+        V = TE->VectorizedValue;
       setInsertPointAfterBundle(E);
       V = FinalShuffle(V, E, VecTy, IsSigned);
       E->VectorizedValue = V;

llvm/test/Transforms/SLPVectorizer/X86/gather_extract_from_vectorbuild.ll

@@ -31,3 +31,30 @@ loop:
   %i4 = extractelement <2 x float> %ins1, i64 0
   br label %loop
 }
+
+define void @test1() {
+; CHECK-LABEL: define void @test1() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[TMP0:%.*]] = phi <2 x float> [ zeroinitializer, [[ENTRY:%.*]] ], [ [[TMP2:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = fadd <2 x float> zeroinitializer, [[TMP0]]
+; CHECK-NEXT:    [[TMP2]] = select <2 x i1> zeroinitializer, <2 x float> [[TMP1]], <2 x float> zeroinitializer
+; CHECK-NEXT:    br label [[LOOP]]
+;
+entry:
+  br label %loop
+
+loop:
+  %ph0 = phi float [ 0.000000e+00, %entry ], [ %i4, %loop ]
+  %ph1 = phi float [ 0.000000e+00, %entry ], [ %i5, %loop ]
+  %i = fadd float 0.000000e+00, %ph0
+  %i1 = fadd float 0.000000e+00, %ph1
+  %i2 = select i1 false, float %i, float 0.000000e+00
+  %i3 = select i1 false, float %i1, float 0.000000e+00
+  %ins0 = insertelement <2 x float> zeroinitializer, float %i2, i64 0
+  %ins1 = insertelement <2 x float> %ins0, float %i3, i64 1
+  %i4 = extractelement <2 x float> %ins1, i64 0
+  %i5 = extractelement <2 x float> %ins1, i64 1
+  br label %loop
+}