If constant widths differ pick larger one

Author: mbrkusanin

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

@@ -4652,9 +4652,14 @@ bool CombinerHelper::matchReassocFoldConstantsInSubTree(GPtrAdd &MI,
   if (!C2)
     return false;
 
+  // If constant widths differ pick larger one.
+  unsigned BitWidth = std::max(C1->getBitWidth(), C2->getBitWidth());
+  APInt NewConst = C1->sext(BitWidth) + C2->sext(BitWidth);
+  LLT Type =
+      MRI.getType(C1->getBitWidth() > C2->getBitWidth() ? LHSSrc2 : Src2Reg);
+
   MatchInfo = [=, &MI](MachineIRBuilder &B) {
-    auto NewCst = B.buildConstant(MRI.getType(Src2Reg),
-                                  C1->sextOrTrunc(C2->getBitWidth()) + *C2);
+    auto NewCst = B.buildConstant(Type, NewConst);
     Observer.changingInstr(MI);
     MI.getOperand(1).setReg(LHSSrc1);
     MI.getOperand(2).setReg(NewCst.getReg(0));

llvm/test/CodeGen/AMDGPU/GlobalISel/combine-ptradd-reassociation.mir

@@ -13,8 +13,8 @@ body:             |
     ; CHECK-NEXT: {{  $}}
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY $sgpr0_sgpr1
     ; CHECK-NEXT: [[INTTOPTR:%[0-9]+]]:_(p1) = G_INTTOPTR [[COPY]](s64)
-    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 12
-    ; CHECK-NEXT: [[PTR_ADD:%[0-9]+]]:_(p1) = G_PTR_ADD [[INTTOPTR]], [[C]](s32)
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 12
+    ; CHECK-NEXT: [[PTR_ADD:%[0-9]+]]:_(p1) = G_PTR_ADD [[INTTOPTR]], [[C]](s64)
     ; CHECK-NEXT: SI_RETURN implicit [[PTR_ADD]](p1)
     %0:_(s64) = COPY $sgpr0_sgpr1
     %1:_(s64) = G_CONSTANT i64 8