Use getSignedTargetConstant for offset (llvm#141149)

This is to fix an assertion failure with PeepholePPC64. The load/store
offset can be negative. A reduced case from one of our failures is added
as well.

Author: scui-ibm

llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp

@@ -7858,8 +7858,8 @@ void PPCDAGToDAGISel::PeepholePPC64() {
         if (!isInt<16>(Offset))
           continue;
 
-        ImmOpnd = CurDAG->getTargetConstant(Offset, SDLoc(ImmOpnd),
-                                            ImmOpnd.getValueType());
+        ImmOpnd = CurDAG->getSignedTargetConstant(Offset, SDLoc(ImmOpnd),
+                                                  ImmOpnd.getValueType());
       } else if (Offset != 0) {
         // This optimization is performed for non-TOC-based local-[exec|dynamic]
         // accesses.

llvm/test/CodeGen/PowerPC/signed-offset.ll

@@ -0,0 +1,34 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -verify-machineinstrs < %s -mcpu=ppc -mtriple powerpc-ibm-aix-xcoff \
+; RUN:     -ppc-asm-full-reg-names | FileCheck %s
+
+%_type = type <{ [90112 x i8] }>
+
+@g = external global %_type
+
+define void @foo(ptr %p) {
+; CHECK-LABEL: foo:
+; CHECK:         stfd f31, 0(r31)
+; CHECK-NEXT:    lwz r3, -32(r30)
+; CHECK-NEXT:    lwz r4, -28(r30)
+; CHECK-NEXT:    cmplwi r3, 0
+; CHECK-NEXT:    cmpwi cr1, r3, 0
+; CHECK-NEXT:    crandc 4*cr5+lt, 4*cr1+gt, eq
+; CHECK-NEXT:    cmpwi cr1, r4, 0
+entry:
+  %0 = load double, ptr getelementptr inbounds nuw (i8, ptr @g, i32 83272), align 8
+  %1 = call i32 @bar(ptr getelementptr inbounds nuw (i8, ptr @g, i32 83272))
+  %2 = call i32 @bar(ptr getelementptr inbounds nuw (i8, ptr @g, i32 83240))
+  store double %0, ptr %p, align 8
+  %3 = load i64, ptr getelementptr inbounds nuw (i8, ptr @g, i32 83240), align 8
+  %4 = icmp slt i64 %3, 1
+  br i1 %4, label %then, label %else
+
+then:                                                     ; preds = %entry
+  ret void
+
+else:                                                     ; preds = %entry
+  ret void
+}
+
+declare signext i32 @bar(ptr)