[clang] [llvm] [Clang] Show inlining hints for __attribute__((warning/error)) (PR #174892)

[Justin Stitt via cfe-commits]

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@@ -6064,13 +6064,23 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
   if (getDebugInfo() && TargetDecl && TargetDecl->hasAttr<MSAllocatorAttr>())
     getDebugInfo()->addHeapAllocSiteMetadata(CI, RetTy->getPointeeType(), Loc);
 
-  // Add metadata if calling an __attribute__((error(""))) or warning fn.
-  if (TargetDecl && TargetDecl->hasAttr<ErrorAttr>()) {
-    llvm::ConstantInt *Line =
-        llvm::ConstantInt::get(Int64Ty, Loc.getRawEncoding());
-    llvm::ConstantAsMetadata *MD = llvm::ConstantAsMetadata::get(Line);
-    llvm::MDTuple *MDT = llvm::MDNode::get(getLLVMContext(), {MD});
-    CI->setMetadata("srcloc", MDT);
+  // Add srcloc metadata for [[gnu::error/warning]] diagnostics. Track
+  // inline/static calls for the heuristic fallback when debug info is not
+  // available. This heuristic is conservative and best-effort since static or
+  // inline-annotated functions are still not guaranteed to be inlined.
+  if (TargetDecl) {
+    bool NeedSrcLoc = TargetDecl->hasAttr<ErrorAttr>();
+    if (!NeedSrcLoc) {
+      if (const auto *FD = dyn_cast<FunctionDecl>(TargetDecl))
+        NeedSrcLoc = FD->isInlined() || FD->hasAttr<AlwaysInlineAttr>() ||
+                     FD->getStorageClass() == SC_Static ||
+                     FD->isInAnonymousNamespace();
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JustinStitt wrote:

> This is imposing a non-zero cost on all code, whether or not it uses ErrorAttr. Imposing a cost on everyone for the sake of the Linux kernel isn't great.

The cost is a dyn_cast-check and some short-circuitable trivial checks. The most expensive check after the dynamic cast is probably the `hasAttr` check. I don't see how I can avoid it :(

> How much does this cost? Do we expect diagnostics that are relevant outside the Linux kernel to use this?

I put some benchmarks I ran a couple of weeks ago in the PR description.



https://github.com/llvm/llvm-project/pull/174892