[Metadata] Try to merge the first and last ranges. (llvm#101860)

Fixes llvm#101859.

If we have at least 2 ranges, we have to try to merge the last and first
ones to handle the wrap range.

(cherry picked from commit 4377656)

Author: dianqk

llvm/lib/IR/Metadata.cpp

@@ -1318,10 +1318,11 @@ MDNode *MDNode::getMostGenericRange(MDNode *A, MDNode *B) {
     ++BI;
   }
 
-  // If we have more than 2 ranges (4 endpoints) we have to try to merge
+  // We haven't handled wrap in the previous merge,
+  // if we have at least 2 ranges (4 endpoints) we have to try to merge
   // the last and first ones.
   unsigned Size = EndPoints.size();
-  if (Size > 4) {
+  if (Size > 2) {
     ConstantInt *FB = EndPoints[0];
     ConstantInt *FE = EndPoints[1];
     if (tryMergeRange(EndPoints, FB, FE)) {

llvm/test/Transforms/GVN/merge-range.ll

@@ -0,0 +1,20 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=gvn -S < %s | FileCheck %s
+
+define i8 @foo(ptr %arg, i8 %arg1) {
+; CHECK-LABEL: define i8 @foo(
+; CHECK-SAME: ptr [[ARG:%.*]], i8 [[ARG1:%.*]]) {
+; CHECK-NEXT:  [[BB:.*:]]
+; CHECK-NEXT:    [[I:%.*]] = load i8, ptr [[ARG]], align 1, !range [[RNG0:![0-9]+]]
+; CHECK-NEXT:    [[I3:%.*]] = add i8 [[I]], [[I]]
+; CHECK-NEXT:    ret i8 [[I3]]
+;
+bb:
+  %i = load i8, ptr %arg, align 1, !range !{i8 127, i8 -20}
+  %i2 = load i8, ptr %arg, align 1, !range !{i8 -27, i8 -24, i8 -20, i8 -17}
+  %i3 = add i8 %i, %i2
+  ret i8 %i3
+}
+;.
+; CHECK: [[RNG0]] = !{i8 127, i8 -17}
+;.