Fix for IGCVectorizer insertpoint

Now for small blocks consisting of 2 special case instructions
PHI & Terminator (BR or RET for example) we return not
firstnonPHI but the last PHI.

(cherry picked from commit 0b9518e)

Author: esukhov

IGC/Compiler/CISACodeGen/IGCVectorizer.cpp

@@ -460,6 +460,8 @@ Instruction *IGCVectorizer::getInsertPointForVector(VecArr &Arr) {
   // if insert point is PHI, shift it to the first nonPHI to be safe
   if (llvm::isa<llvm::PHINode>(InsertPoint))
       InsertPoint = InsertPoint->getParent()->getFirstNonPHI();
+  if (InsertPoint->isTerminator())
+      InsertPoint = InsertPoint->getPrevNonDebugInstruction();
 
   return InsertPoint;
 }

IGC/Compiler/tests/IGCVectorizer/vectorizer-special-bb-to-insert.ll

@@ -0,0 +1,70 @@
+;=========================== begin_copyright_notice ============================
+;
+; Copyright (C) 2025 Intel Corporation
+;
+; SPDX-License-Identifier: MIT
+;
+;============================ end_copyright_notice =============================
+
+; RUN: igc_opt -S  --igc-vectorizer -dce --regkey=VectorizerDepWindowMultiplier=6 < %s 2>&1 | FileCheck %s
+
+; CHECK-LABEL: bb3:
+; CHECK-NEXT: [[PHI:%.*]] = phi float
+; CHECK-NEXT: [[VECTOR_0:%.*]] = insertelement <8 x float> undef, float [[PHI]], i32 0
+; CHECK-NEXT: [[VECTOR_1:%.*]] = insertelement <8 x float> [[VECTOR_0]], float [[PHI]], i32 1
+; CHECK-NEXT: [[VECTOR_2:%.*]] = insertelement <8 x float> [[VECTOR_1]], float [[PHI]], i32 2
+; CHECK-NEXT: [[VECTOR_3:%.*]] = insertelement <8 x float> [[VECTOR_2]], float [[PHI]], i32 3
+; CHECK-NEXT: [[VECTOR_4:%.*]] = insertelement <8 x float> [[VECTOR_3]], float [[PHI]], i32 4
+; CHECK-NEXT: [[VECTOR_5:%.*]] = insertelement <8 x float> [[VECTOR_4]], float [[PHI]], i32 5
+; CHECK-NEXT: [[VECTOR_6:%.*]] = insertelement <8 x float> [[VECTOR_5]], float [[PHI]], i32 6
+; CHECK-NEXT: [[VECTOR_7:%.*]] = insertelement <8 x float> [[VECTOR_6]], float [[PHI]], i32 7
+; CHECK-NEXT: br i1 {{%.*}}, label {{%.*}}, label {{%.*}}
+
+
+define spir_kernel void @barney() {
+bb:
+  %tmp = fcmp une float 0.000000e+00, 0.000000e+00
+  br label %bb1
+
+bb1:                                              ; preds = %bb
+  br i1 false, label %bb3, label %bb2
+
+bb2:                                              ; preds = %bb1
+  br label %bb3
+
+bb3:                                              ; preds = %bb2, %bb1
+  %tmp4 = phi float [ 0.000000e+00, %bb1 ], [ 0.000000e+00, %bb2 ]
+  br i1 %tmp, label %bb5, label %bb6
+
+bb5:                                              ; preds = %bb3
+  br label %bb6
+
+bb6:                                              ; preds = %bb5, %bb3
+  %tmp7 = fmul reassoc nsz arcp contract float 0.000000e+00, %tmp4
+  %tmp8 = fmul reassoc nsz arcp contract float 0.000000e+00, %tmp4
+  %tmp9 = fmul reassoc nsz arcp contract float 0.000000e+00, %tmp4
+  %tmp10 = fmul reassoc nsz arcp contract float 0.000000e+00, %tmp4
+  %tmp11 = fmul reassoc nsz arcp contract float 0.000000e+00, %tmp4
+  %tmp12 = fmul reassoc nsz arcp contract float 0.000000e+00, %tmp4
+  %tmp13 = fmul reassoc nsz arcp contract float 0.000000e+00, %tmp4
+  %tmp14 = fmul reassoc nsz arcp contract float 0.000000e+00, %tmp4
+  %tmp15 = insertelement <8 x float> zeroinitializer, float %tmp7, i64 0
+  %tmp16 = insertelement <8 x float> %tmp15, float %tmp8, i64 1
+  %tmp17 = insertelement <8 x float> %tmp16, float %tmp9, i64 2
+  %tmp18 = insertelement <8 x float> %tmp17, float %tmp10, i64 3
+  %tmp19 = insertelement <8 x float> %tmp18, float %tmp11, i64 4
+  %tmp20 = insertelement <8 x float> %tmp19, float %tmp12, i64 5
+  %tmp21 = insertelement <8 x float> %tmp20, float %tmp13, i64 6
+  %tmp22 = insertelement <8 x float> %tmp21, float %tmp14, i64 7
+  %tmp23 = bitcast <8 x float> %tmp22 to <8 x i32>
+  call void @llvm.genx.GenISA.LSC2DBlockWrite.v8i32(i64 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i1 false, i1 false, i32 0, <8 x i32> %tmp23)
+  ret void
+}
+
+declare void @llvm.genx.GenISA.LSC2DBlockWrite.v8i32(i64, i32, i32, i32, i32, i32, i32, i32, i32, i32, i1, i1, i32, <8 x i32>)
+
+!igc.functions = !{!0}
+
+!0 = distinct !{void ()* @barney, !1}
+!1 = distinct !{!2}
+!2 = distinct !{!"sub_group_size", i32 16}