[SLP]Fix minbiwidth analysis for gather nodes with SIToFP users

If the buildvector node has cast to float user, it cannot be considered as safe
for truncation, need to use the original bitwidth here.

Fixes #135410

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -19974,8 +19974,10 @@ void BoUpSLP::computeMinimumValueSizes() {
                       return false;
                     if (!isa<CastInst, BinaryOperator, FreezeInst, PHINode,
                              SelectInst>(U) ||
+                        isa<SIToFPInst, UIToFPInst>(U) ||
                         !isa<CastInst, BinaryOperator, FreezeInst, PHINode,
-                             SelectInst>(UserTE->getMainOp()))
+                             SelectInst>(UserTE->getMainOp()) ||
+                        isa<SIToFPInst, UIToFPInst>(UserTE->getMainOp()))
                       return true;
                     unsigned UserTESz = DL->getTypeSizeInBits(
                         UserTE->Scalars.front()->getType());

llvm/test/Transforms/SLPVectorizer/X86/trunced-buildvector-scalar-extended.ll

@@ -5,9 +5,8 @@ define <4 x float> @test(i64 %0) {
 ; CHECK-LABEL: define <4 x float> @test(
 ; CHECK-SAME: i64 [[TMP0:%.*]]) {
 ; CHECK-NEXT:  [[ENTRY:.*:]]
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[TMP0]] to i32
-; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <4 x i32> <i32 0, i32 0, i32 poison, i32 0>, i32 [[TMP1]], i32 2
-; CHECK-NEXT:    [[TMP3:%.*]] = sext <4 x i32> [[TMP2]] to <4 x i64>
+; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <4 x i64> <i64 0, i64 0, i64 poison, i64 0>, i64 [[TMP0]], i32 2
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc <4 x i64> [[TMP3]] to <4 x i32>
 ; CHECK-NEXT:    [[TMP4:%.*]] = sitofp <4 x i64> [[TMP3]] to <4 x float>
 ; CHECK-NEXT:    [[TMP5:%.*]] = sitofp <4 x i32> [[TMP2]] to <4 x float>
 ; CHECK-NEXT:    [[TMP6:%.*]] = fadd <4 x float> [[TMP4]], [[TMP5]]