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

vectorized.

When trying to reuse the extractelement instruction, emitted for the
insertelement instruction, need to check, if the this insertelement
instruction was vectorized. In this case, need to use vectorized value,
not the original insertelement.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -11905,8 +11905,10 @@ Value *BoUpSLP::vectorizeTree(
         if (!Ex) {
           // "Reuse" the existing extract to improve final codegen.
           if (auto *ES = dyn_cast<ExtractElementInst>(Scalar)) {
-            Ex = Builder.CreateExtractElement(ES->getOperand(0),
-                                              ES->getOperand(1));
+            Value *V = ES->getVectorOperand();
+            if (const TreeEntry *ETE = getTreeEntry(V))
+              V = ETE->VectorizedValue;
+            Ex = Builder.CreateExtractElement(V, ES->getIndexOperand());
           } else {
             Ex = Builder.CreateExtractElement(Vec, Lane);
           }

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

@@ -58,3 +58,48 @@ loop:
   %i5 = extractelement <2 x float> %ins1, i64 1
   br label %loop
 }
+
+define void @test2() {
+; CHECK-LABEL: define void @test2() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[BB3:%.*]]
+; CHECK:       bb1:
+; CHECK-NEXT:    [[PH:%.*]] = phi float [ poison, [[BB2:%.*]] ], [ [[TMP3:%.*]], [[LOOP:%.*]] ]
+; CHECK-NEXT:    unreachable
+; CHECK:       bb2:
+; CHECK-NEXT:    br i1 poison, label [[BB3]], label [[BB1:%.*]]
+; CHECK:       bb3:
+; CHECK-NEXT:    br label [[LOOP]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[TMP0:%.*]] = phi <2 x float> [ zeroinitializer, [[BB3]] ], [ [[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:    [[TMP3]] = extractelement <2 x float> [[TMP2]], i64 1
+; CHECK-NEXT:    br i1 poison, label [[BB1]], label [[LOOP]]
+;
+entry:
+  br label %bb3
+
+bb1:
+  %ph = phi float [ poison, %bb2 ], [ %i5, %loop ]
+  unreachable
+
+bb2:
+  br i1 poison, label %bb3, label %bb1
+
+bb3:
+  br label %loop
+
+loop:
+  %ph0 = phi float [ 0.000000e+00, %bb3 ], [ %i4, %loop ]
+  %ph1 = phi float [ 0.000000e+00, %bb3 ], [ %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 i1 poison, label %bb1, label %loop
+}