[llvm] [FunctionComparator] Differentiate instructions passing distinct MDStrings (PR #69543)

[Duncan P. N. Exon Smith via llvm-commits]

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@@ -160,10 +160,23 @@ int FunctionComparator::cmpAttrs(const AttributeList L,
 int FunctionComparator::cmpMetadata(const Metadata *L,
                                     const Metadata *R) const {
   // TODO: the following routine coerce the metadata contents into constants
-  // before comparison.
+  // or MDStrings before comparison.
   // It ignores any other cases, so that the metadata nodes are considered
   // equal even though this is not correct.
   // We should structurally compare the metadata nodes to be perfect here.
+
+  auto *MDStringL = dyn_cast<MDString>(L);
+  auto *MDStringR = dyn_cast<MDString>(R);
+  if (MDStringL && MDStringR) {
+    if (MDStringL == MDStringR)
+      return 0;
+    return MDStringL->getString().compare(MDStringR->getString());
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dexonsmith wrote:

This shouldn't be necessary. `MDString`s are guaranteed to be uniqued by content.

https://github.com/llvm/llvm-project/pull/69543