Enhance type safety checks in LegalizationPass

Adds an element type (EltTy) comparison to ensure ExtractElementInst (EEI) instances have the same element size as the original type.

Author: ustachow

IGC/Compiler/LegalizationPass.cpp

@@ -563,7 +563,7 @@ LegalizeGVNBitCastPattern(IRBuilder<>* Builder, const DataLayout* DL,
         // Assign null to BI if this is not ending with a bitcast.
         BI = dyn_cast<BitCastInst>(TI->user_back());
 
-        // This gurantees all uses of BI could be replaced by the source.
+        // This guarantees all uses of BI could be replaced by the source.
         if (BI && BI->getType() != EltTy)
             return false;
         else if (TI->getType()->getPrimitiveSizeInBits() !=
@@ -594,11 +594,11 @@ LegalizeGVNBitCastPattern(IRBuilder<>* Builder, const DataLayout* DL,
         if (!BI || !BI->getType()->isVectorTy())
             return false;
 
-        // All uses must be EEI.
+        // All uses must be EEI and must have the same element size as the original element type.
         for (auto U : BI->users())
         {
             auto EEI = dyn_cast<ExtractElementInst>(U);
-            if (!EEI)
+            if (!EEI || EEI->getType()->getPrimitiveSizeInBits() != EltTy->getPrimitiveSizeInBits())
                 return false;
             EEIs.push_back(EEI);
         }

IGC/Compiler/tests/Legalization/bitcast-same-element-size.ll

@@ -0,0 +1,34 @@
+;=========================== begin_copyright_notice ============================
+;
+; Copyright (C) 2025 Intel Corporation
+;
+; SPDX-License-Identifier: MIT
+;
+;============================ end_copyright_notice =============================
+;
+; RUN: igc_opt -igc-legalization -verify -S %s -o - | FileCheck %s
+
+; ------------------------------------------------
+; Legalization: bitcast illegal types after GVN
+; ------------------------------------------------
+
+define i16 @test_bitcast_pattern2(<4 x float> %src1, i32 %src2) {
+; CHECK-LABEL: define i16 @test_bitcast_pattern2(
+; CHECK-SAME: <4 x float> [[SRC1:%.*]], i32 [[SRC2:%.*]]) {
+; CHECK: [[TMP2:%.*]] = bitcast <4 x float> [[SRC1]] to <2 x i64>
+; CHECK-NEXT: [[TMP3:%.*]] = extractelement <2 x i64> [[TMP2]], i32 0
+; CHECK-NEXT: [[TMP4:%.*]] = bitcast i64 [[TMP3]] to <4 x i16>
+; CHECK-NEXT: [[TMP5:%.*]] = extractelement <4 x i16> [[TMP4]], i32 1
+; CHECK-NEXT: ret i16 [[TMP5]]
+;
+  %1 = bitcast <4 x float> %src1 to i128
+  %2 = trunc i128 %1 to i64
+  %3 = bitcast i64 %2 to <4 x i16>
+  %4 = extractelement <4 x i16> %3, i32 1
+  ret i16 %4
+}
+
+!igc.functions = !{!0}
+
+!0 = !{i16 (<4 x float>, i32)* @test_bitcast_pattern2, !1}
+!1 = !{}