[InstCombine] Support nusw in icmp of gep with base

Proof: https://alive2.llvm.org/ce/z/omnQXt

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -691,7 +691,8 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
     RHS = RHS->stripPointerCasts();
 
   Value *PtrBase = GEPLHS->getOperand(0);
-  if (PtrBase == RHS && (GEPLHS->isInBounds() || ICmpInst::isEquality(Cond))) {
+  if (PtrBase == RHS &&
+      (GEPLHS->hasNoUnsignedSignedWrap() || ICmpInst::isEquality(Cond))) {
     // ((gep Ptr, OFFSET) cmp Ptr)   ---> (OFFSET cmp 0).
     Value *Offset = EmitGEPOffset(GEPLHS);
     return new ICmpInst(ICmpInst::getSignedPredicate(Cond), Offset,

llvm/test/Transforms/InstCombine/icmp-gep.ll

@@ -133,6 +133,16 @@ define i1 @ult_base_inbounds(ptr %x, i64 %y) {
   ret i1 %r
 }
 
+define i1 @ult_base_nusw(ptr %x, i64 %y) {
+; CHECK-LABEL: @ult_base_nusw(
+; CHECK-NEXT:    [[R:%.*]] = icmp slt i64 [[Y:%.*]], 0
+; CHECK-NEXT:    ret i1 [[R]]
+;
+  %g = getelementptr nusw i8, ptr %x, i64 %y
+  %r = icmp ult ptr %g, %x
+  ret i1 %r
+}
+
 define i1 @ugt_base_inbounds_commute(i64 %y) {
 ; CHECK-LABEL: @ugt_base_inbounds_commute(
 ; CHECK-NEXT:    [[X:%.*]] = call ptr @getptr()