[LV] Add test for re-using existing phi for SCEV Add.

Add another test case for
#147824, where the difference
between an existing phi and the target SCEV is an add of a constant.

Author: fhahn

llvm/test/Transforms/LoopVectorize/reuse-lcssa-phi-scev-expansion.ll

@@ -386,6 +386,95 @@ exit:
   ret void
 }
 
+
+declare i1 @cond()
+
+define void @scev_exp_reuse_const_add(ptr %dst, ptr %src) {
+; CHECK-LABEL: define void @scev_exp_reuse_const_add(
+; CHECK-SAME: ptr [[DST:%.*]], ptr [[SRC:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[SRC2:%.*]] = ptrtoint ptr [[SRC]] to i64
+; CHECK-NEXT:    [[DST1:%.*]] = ptrtoint ptr [[DST]] to i64
+; CHECK-NEXT:    br label %[[LOOP_1:.*]]
+; CHECK:       [[LOOP_1]]:
+; CHECK-NEXT:    [[INDVAR:%.*]] = phi i64 [ [[INDVAR_NEXT:%.*]], %[[LOOP_1]] ], [ 0, %[[ENTRY]] ]
+; CHECK-NEXT:    [[PTR_IV_1:%.*]] = phi ptr [ [[DST]], %[[ENTRY]] ], [ [[PTR_IV_1_NEXT:%.*]], %[[LOOP_1]] ]
+; CHECK-NEXT:    [[PTR_IV_1_NEXT]] = getelementptr i8, ptr [[PTR_IV_1]], i64 2
+; CHECK-NEXT:    [[C:%.*]] = call i1 @cond()
+; CHECK-NEXT:    [[INDVAR_NEXT]] = add i64 [[INDVAR]], 1
+; CHECK-NEXT:    br i1 [[C]], label %[[LOOP_2_PH:.*]], label %[[LOOP_1]]
+; CHECK:       [[LOOP_2_PH]]:
+; CHECK-NEXT:    [[INDVAR_LCSSA:%.*]] = phi i64 [ [[INDVAR]], %[[LOOP_1]] ]
+; CHECK-NEXT:    [[PTR_IV_1_NEXT_LCSSA:%.*]] = phi ptr [ [[PTR_IV_1_NEXT]], %[[LOOP_1]] ]
+; CHECK-NEXT:    br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_MEMCHECK:.*]]
+; CHECK:       [[VECTOR_MEMCHECK]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = sub i64 [[DST1]], [[SRC2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shl i64 [[INDVAR_LCSSA]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = add i64 [[TMP1]], [[TMP0]]
+; CHECK-NEXT:    [[DIFF_CHECK:%.*]] = icmp ult i64 [[TMP2]], 4
+; CHECK-NEXT:    br i1 [[DIFF_CHECK]], label %[[SCALAR_PH]], label %[[VECTOR_PH:.*]]
+; CHECK:       [[VECTOR_PH]]:
+; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr i8, ptr [[PTR_IV_1_NEXT_LCSSA]], i64 80
+; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
+; CHECK:       [[VECTOR_BODY]]:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[OFFSET_IDX:%.*]] = mul i64 [[INDEX]], 2
+; CHECK-NEXT:    [[NEXT_GEP:%.*]] = getelementptr i8, ptr [[PTR_IV_1_NEXT_LCSSA]], i64 [[OFFSET_IDX]]
+; CHECK-NEXT:    [[TMP4:%.*]] = add i64 [[INDEX]], 1
+; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr i16, ptr [[SRC]], i64 [[TMP4]]
+; CHECK-NEXT:    [[TMP6:%.*]] = getelementptr i16, ptr [[TMP5]], i32 0
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <2 x i16>, ptr [[TMP6]], align 2
+; CHECK-NEXT:    [[TMP7:%.*]] = getelementptr i16, ptr [[NEXT_GEP]], i32 0
+; CHECK-NEXT:    store <2 x i16> [[WIDE_LOAD]], ptr [[TMP7]], align 2
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 2
+; CHECK-NEXT:    [[TMP8:%.*]] = icmp eq i64 [[INDEX_NEXT]], 40
+; CHECK-NEXT:    br i1 [[TMP8]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP10:![0-9]+]]
+; CHECK:       [[MIDDLE_BLOCK]]:
+; CHECK-NEXT:    br i1 false, label %[[EXIT:.*]], label %[[SCALAR_PH]]
+; CHECK:       [[SCALAR_PH]]:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ 40, %[[MIDDLE_BLOCK]] ], [ 0, %[[LOOP_2_PH]] ], [ 0, %[[VECTOR_MEMCHECK]] ]
+; CHECK-NEXT:    [[BC_RESUME_VAL3:%.*]] = phi ptr [ [[TMP3]], %[[MIDDLE_BLOCK]] ], [ [[PTR_IV_1_NEXT_LCSSA]], %[[LOOP_2_PH]] ], [ [[PTR_IV_1_NEXT_LCSSA]], %[[VECTOR_MEMCHECK]] ]
+; CHECK-NEXT:    br label %[[LOOP_2:.*]]
+; CHECK:       [[LOOP_2]]:
+; CHECK-NEXT:    [[IV_1:%.*]] = phi i64 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[IV_2_NEXT:%.*]], %[[LOOP_2]] ]
+; CHECK-NEXT:    [[PTR_IV_2:%.*]] = phi ptr [ [[BC_RESUME_VAL3]], %[[SCALAR_PH]] ], [ [[PTR_IV_2_NEXT:%.*]], %[[LOOP_2]] ]
+; CHECK-NEXT:    [[IV_2_NEXT]] = add i64 [[IV_1]], 1
+; CHECK-NEXT:    [[GEP_SRC_1:%.*]] = getelementptr i16, ptr [[SRC]], i64 [[IV_2_NEXT]]
+; CHECK-NEXT:    [[L:%.*]] = load i16, ptr [[GEP_SRC_1]], align 2
+; CHECK-NEXT:    [[PTR_IV_2_NEXT]] = getelementptr i8, ptr [[PTR_IV_2]], i64 2
+; CHECK-NEXT:    store i16 [[L]], ptr [[PTR_IV_2]], align 2
+; CHECK-NEXT:    [[EC:%.*]] = icmp eq i64 [[IV_1]], 40
+; CHECK-NEXT:    br i1 [[EC]], label %[[EXIT]], label %[[LOOP_2]], !llvm.loop [[LOOP11:![0-9]+]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop.1
+
+loop.1:
+  %ptr.iv.1 = phi ptr [ %dst, %entry ], [ %ptr.iv.1.next, %loop.1 ]
+  %ptr.iv.1.next = getelementptr i8, ptr %ptr.iv.1, i64 2
+  %c = call i1 @cond()
+  br i1 %c, label %loop.2.ph, label %loop.1
+
+loop.2.ph:
+  br label %loop.2
+
+loop.2:
+  %iv.1 = phi i64 [ 0, %loop.2.ph ], [ %iv.2.next, %loop.2 ]
+  %ptr.iv.2 = phi ptr [ %ptr.iv.1.next, %loop.2.ph ], [ %ptr.iv.2.next, %loop.2 ]
+  %iv.2.next = add i64 %iv.1, 1
+  %gep.src.1 = getelementptr i16, ptr %src, i64 %iv.2.next
+  %l = load i16, ptr %gep.src.1, align 2
+  %ptr.iv.2.next = getelementptr i8, ptr %ptr.iv.2, i64 2
+  store i16 %l, ptr %ptr.iv.2, align 2
+  %ec = icmp eq i64 %iv.1, 40
+  br i1 %ec, label %exit, label %loop.2
+
+exit:
+  ret void
+}
+
 ; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
 declare double @llvm.cos.f64(double) #0