[IGC Core] Fix ICmp instruction promotion during type legalization

Fix mask creation when promoting icmp instruction during type
legalization

Author: againull

IGC/Compiler/Legalizer/InstPromoter.cpp

@@ -120,8 +120,10 @@ bool InstPromoter::visitICmpInst(ICmpInst &I) {
   unsigned finalWidth = LHS->getType()->getIntegerBitWidth();
 
   if (!isSigned) {
-    LHS = IRB->CreateAnd(LHS, (1 << initialWidth) - 1);
-    RHS = IRB->CreateAnd(RHS, (1 << initialWidth) - 1);
+    APInt M = APInt::getLowBitsSet(finalWidth, initialWidth);
+    auto *MaskC = ConstantInt::get(LHS->getType(), M);
+    LHS = IRB->CreateAnd(LHS, MaskC);
+    RHS = IRB->CreateAnd(RHS, MaskC);
   } else {
     IGC_ASSERT(finalWidth >= initialWidth);
 

IGC/Compiler/tests/TypeLegalizer/promote-cmp.ll

@@ -0,0 +1,28 @@
+;=========================== begin_copyright_notice ============================
+;
+; Copyright (C) 2025 Intel Corporation
+;
+; SPDX-License-Identifier: MIT
+;
+;============================ end_copyright_notice =============================
+;
+; RUN: igc_opt -igc-type-legalizer -S < %s | FileCheck %s
+; ------------------------------------------------
+; Legalization: icmp (i40 -> i64 promotion mask correctness)
+; ------------------------------------------------
+;
+; Ensure that unsigned icmp on an illegal integer width (i40) is promoted
+; with a correct low-40-bit mask (0xFFFFFFFFFF = 1099511627775).
+;
+; CHECK-LABEL: define i1 @test_icmp_i40
+; CHECK: %[[TRUNC:.*]] = and i64 %[[X:.*]], 1099511627775
+; CHECK: %[[MASKED:.*]] = and i64 %[[TRUNC]], 1099511627775
+; CHECK: icmp ult i64 %[[MASKED]], 4294967296
+; CHECK: ret i1
+
+define i1 @test_icmp_i40(i64 %x) {
+  ; Truncate to illegal width i40, then compare with 1<<32
+  %t = trunc i64 %x to i40
+  %cmp = icmp ult i40 %t, 4294967296
+  ret i1 %cmp
+}