release/19.x: [Metadata] Try to merge the first and last ranges. (#101860)

[llvmbot]

Backport 4377656

Requested by: @DianQK

[llvmbot]

@dtcxzyw What do you think about merging this PR to the release branch?

[llvmbot]

@llvm/pr-subscribers-llvm-ir

@llvm/pr-subscribers-llvm-transforms

Author: None (llvmbot)

Changes

Backport 4377656

Requested by: @DianQK

---

Full diff: https://github.com/llvm/llvm-project/pull/101875.diff

2 Files Affected:

• (modified) llvm/lib/IR/Metadata.cpp (+3-2)
• (added) llvm/test/Transforms/GVN/merge-range.ll (+20)

diff --git a/llvm/lib/IR/Metadata.cpp b/llvm/lib/IR/Metadata.cpp
index ae5f5de142328..fd2f4d184162f 100644
--- a/llvm/lib/IR/Metadata.cpp
+++ b/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)) {
diff --git a/llvm/test/Transforms/GVN/merge-range.ll b/llvm/test/Transforms/GVN/merge-range.ll
new file mode 100644
index 0000000000000..ad1fa4cae5662
--- /dev/null
+++ b/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}
+;.

[tru]

Is this a important fix to backport? It looks a bit more like a feature than a bugfix, but I am not that well versed with this code.

[nikic]

@tru This is a bug fix to prevent emission of invalid IR.

[github-actions]

@DianQK (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.