[Mlir-commits] [mlir] [mlir][LLVMIR] Bound import diagnostics and share one slot tracker (PR #229956)

[Tobias Gysi]

================
@@ -52,25 +53,61 @@ using namespace mlir::LLVM::detail;
 
 #include "mlir/Dialect/LLVMIR/LLVMConversionEnumsFromLLVM.inc"
 
-// Utility to print an LLVM value as a string for passing to emitError().
-// FIXME: Diagnostic should be able to natively handle types that have
-// operator << (raw_ostream&) defined.
-static std::string diag(const llvm::Value &value) {
+/// Upper bound on the characters a diagnostic renders for an LLVM entity.
+/// One rendering is unbounded by nature: a GlobalVariable prints its entire
+/// initializer, and a node with long MDStrings or large inline constants
+/// prints them whole. On a merged library a single unbounded diagnostic
+/// reaches tens of megabytes, so every rendering path below truncates its
+/// output. Diagnostics only need to identify the entity; the full form is
+/// in the input being imported.
+static constexpr size_t kMaxDiagLength = 256;
+
+static std::string truncateDiag(std::string str) {
+  if (str.size() <= kMaxDiagLength)
+    return str;
+  str.resize(kMaxDiagLength);
+  str += "... <truncated>";
+  return str;
+}
+
+// Prints a metadata node through a caller-provided tracker so module-flag
+// conversion shares the importer's tracker instead of building one per call.
----------------
gysit wrote:

```suggestion
/// Prints a metadata node through a caller-provided tracker so module-flag
/// conversion shares the importer's tracker instead of building one per call.
```
ultra nit:

https://github.com/llvm/llvm-project/pull/229956