[PowerPC] Use getSignedTargetConstant in SelectOptimalAddrMode. (llvm#127305)

Fixes llvm#127298.

(cherry picked from commit 256145b)

Author: topperc

Diff for: llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -19050,8 +19050,8 @@ PPC::AddrMode PPCTargetLowering::SelectOptimalAddrMode(const SDNode *Parent,
         int32_t Addr = (int32_t)CNImm;
         // Otherwise, break this down into LIS + Disp.
         Disp = DAG.getSignedTargetConstant((int16_t)Addr, DL, MVT::i32);
-        Base =
-            DAG.getTargetConstant((Addr - (int16_t)Addr) >> 16, DL, MVT::i32);
+        Base = DAG.getSignedTargetConstant((Addr - (int16_t)Addr) >> 16, DL,
+                                           MVT::i32);
         uint32_t LIS = CNType == MVT::i32 ? PPC::LIS : PPC::LIS8;
         Base = SDValue(DAG.getMachineNode(LIS, DL, CNType, Base), 0);
         break;

Diff for: llvm/test/CodeGen/PowerPC/pr127298.ll

@@ -0,0 +1,13 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mtriple=powerpc | FileCheck %s
+
+define void @foo() {
+; CHECK-LABEL: foo:
+; CHECK:       # %bb.0: # %Entry
+; CHECK-NEXT:    lis 3, -8530
+; CHECK-NEXT:    lbz 3, -16657(3)
+; CHECK-NEXT:    blr
+Entry:
+  %0 = load volatile i8, ptr inttoptr (i32 -559038737 to ptr), align 1
+  ret void
+}