[InstCombine] Pre-commit tests related to ADDLIKE+GEP->GEP+GEP. NFC

InstCombine can transform ADD+GEP into GEP+GEP. But those rewrites
does not currently trigger when the ADD is a disjoint OR (which
happens to be the canonical form for certain ADD operations). Add
lit tests to show that we are lacking such rewrites.

Also add a test case showing that we do not preserve "inbounds nuw"
and "nuw" when doing such transforms and the ADD/OR is known to be
NUW.

Author: bjope

llvm/test/Transforms/InstCombine/array.ll

@@ -109,6 +109,45 @@ entry:
   ret void
 }
 
+; FIXME: Should be transformed as OR+GEP -> GEP+GEP (similar to gep_inbounds_add_nuw below).
+define ptr @gep_inbounds_nuwaddlike(ptr %ptr, i64 %a, i64 %b) {
+; CHECK-LABEL: define ptr @gep_inbounds_nuwaddlike(
+; CHECK-SAME: ptr [[PTR:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
+; CHECK-NEXT:    [[ADD:%.*]] = or disjoint i64 [[A]], [[B]]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds nuw i32, ptr [[PTR]], i64 [[ADD]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %add = or disjoint i64 %a, %b
+  %gep = getelementptr inbounds nuw i32, ptr %ptr, i64 %add
+  ret ptr %gep
+}
+
+; FIXME: Preserve "inbounds nuw".
+define ptr @gep_inbounds_add_nuw(ptr %ptr, i64 %a, i64 %b) {
+; CHECK-LABEL: define ptr @gep_inbounds_add_nuw(
+; CHECK-SAME: ptr [[PTR:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr i32, ptr [[PTR]], i64 [[A]]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i32, ptr [[TMP1]], i64 [[B]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %add = add nuw i64 %a, %b
+  %gep = getelementptr inbounds nuw i32, ptr %ptr, i64 %add
+  ret ptr %gep
+}
+
+; FIXME: Preserve "nuw".
+define ptr @gep_add_nuw(ptr %ptr, i64 %a, i64 %b) {
+; CHECK-LABEL: define ptr @gep_add_nuw(
+; CHECK-SAME: ptr [[PTR:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr i32, ptr [[PTR]], i64 [[A]]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i32, ptr [[TMP1]], i64 [[B]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %add = add nuw i64 %a, %b
+  %gep = getelementptr nuw i32, ptr %ptr, i64 %add
+  ret ptr %gep
+}
+
 define ptr @gep_inbounds_add_nsw_nonneg(ptr %ptr, i64 %a, i64 %b) {
 ; CHECK-LABEL: define ptr @gep_inbounds_add_nsw_nonneg(
 ; CHECK-SAME: ptr [[PTR:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
@@ -219,6 +258,27 @@ define ptr @gep_inbounds_sext_add_nonneg(ptr %ptr, i32 %a) {
   ret ptr %gep
 }
 
+; FIXME: Could be optimized similar to gep_inbounds_sext_add_nonneg above
+;        (difference is that we are using disjoint OR which is canonical form
+;        of ADD with disjoint operands).
+define ptr @gep_inbounds_sext_addlike_nonneg(ptr %ptr, i32 %a) {
+; CHECK-LABEL: define ptr @gep_inbounds_sext_addlike_nonneg(
+; CHECK-SAME: ptr [[PTR:%.*]], i32 [[A:%.*]]) {
+; CHECK-NEXT:    [[A_NNEG:%.*]] = icmp sgt i32 [[A]], -1
+; CHECK-NEXT:    call void @llvm.assume(i1 [[A_NNEG]])
+; CHECK-NEXT:    [[ADD:%.*]] = or disjoint i32 [[A]], 10
+; CHECK-NEXT:    [[IDX:%.*]] = zext nneg i32 [[ADD]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds nuw i32, ptr [[PTR]], i64 [[IDX]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %a.nneg = icmp sgt i32 %a, -1
+  call void @llvm.assume(i1 %a.nneg)
+  %add = or disjoint i32 %a, 10
+  %idx = sext i32 %add to i64
+  %gep = getelementptr inbounds i32, ptr %ptr, i64 %idx
+  ret ptr %gep
+}
+
 define ptr @gep_inbounds_sext_add_not_nonneg_1(ptr %ptr, i32 %a) {
 ; CHECK-LABEL: define ptr @gep_inbounds_sext_add_not_nonneg_1(
 ; CHECK-SAME: ptr [[PTR:%.*]], i32 [[A:%.*]]) {