[SLP]Fix PR61050: Assertion `I->use_empty() && "trying to erase instruction with users."

When gathering the counter for the reused scalars, need to use reduced
value, not the original reduced value. Same values counter is gathered
for reduced values, not original ones.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -13157,7 +13157,7 @@ class HorizontalReduction {
         for (Value *RdxVal : VL) {
           Value *OrigV = TrackedToOrig.find(RdxVal)->second;
           if (IsSupportedHorRdxIdentityOp) {
-            VectorizedVals.try_emplace(OrigV, SameValuesCounter[OrigV]);
+            VectorizedVals.try_emplace(OrigV, SameValuesCounter[RdxVal]);
             continue;
           }
           ++VectorizedVals.try_emplace(OrigV, 0).first->getSecond();

llvm/test/Transforms/SLPVectorizer/X86/reduction-modified-values.ll

@@ -0,0 +1,32 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S --passes=slp-vectorizer -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
+
+define i32 @test() {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[TMP0:%.*]] = shufflevector <4 x i32> zeroinitializer, <4 x i32> zeroinitializer, <4 x i32> <i32 0, i32 1, i32 2, i32 7>
+; CHECK-NEXT:    [[TMP1:%.*]] = or <4 x i32> [[TMP0]], zeroinitializer
+; CHECK-NEXT:    [[TMP2:%.*]] = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> [[TMP1]])
+; CHECK-NEXT:    [[TMP3:%.*]] = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> [[TMP0]])
+; CHECK-NEXT:    [[OP_RDX:%.*]] = add i32 [[TMP2]], [[TMP3]]
+; CHECK-NEXT:    ret i32 [[OP_RDX]]
+;
+bb:
+  %0 = shufflevector <4 x i32> zeroinitializer, <4 x i32> zeroinitializer, <4 x i32> <i32 0, i32 1, i32 2, i32 7>
+  %1 = extractelement <4 x i32> %0, i32 3
+  %2 = extractelement <4 x i32> %0, i32 2
+  %3 = extractelement <4 x i32> %0, i32 1
+  %4 = extractelement <4 x i32> %0, i32 0
+  %inst514 = or i32 %4, 0
+  %inst494 = or i32 %3, 0
+  %inst474 = or i32 %2, 0
+  %inst454 = or i32 %1, 0
+  %inst458 = add i32 %1, %inst454
+  %inst477 = add i32 %inst458, %2
+  %inst478 = add i32 %inst477, %inst474
+  %inst497 = add i32 %inst478, %3
+  %inst498 = add i32 %inst497, %inst494
+  %inst517 = add i32 %inst498, %4
+  %inst518 = add i32 %inst517, %inst514
+  ret i32 %inst518
+}