[llvm] [CtxProf] emit fatal usage error when flatten-prethinlink runs without guid metadata (PR #194383)

[Arda Serdar Pektezol via llvm-commits]

https://github.com/pektezol created https://github.com/llvm/llvm-project/pull/194383

Fixes #194185

`ctx-prof-flatten-prethinlink` can call `AssignGUIDPass::getGUID()` on defined functions even when the GUID metadata is missing. In that case, LLVM currently asserts on missing `!guid` metadata.

Replace the assertion with `reportFatalUsageError()` so the pass fails with a clear user-facing error, and add a regression test for invoking only `ctx-prof-flatten-prethinlink`.

@boomanaiden154 sorry for the ping, accidentally closed the previous one. I updated the error message.

>From c0a98815d1ad04a982f70fb62d6757f487281fe3 Mon Sep 17 00:00:00 2001
From: Arda Serdar Pektezol <arda at pektezol.dev>
Date: Mon, 27 Apr 2026 17:14:12 +0300
Subject: [PATCH] [CtxProf] emit fatal usage error when flatten-prethinlink
 runs without guid metadata

---
 llvm/lib/Analysis/CtxProfAnalysis.cpp                      | 4 +++-
 .../flatten-prethinlink-requires-guid-metadata.ll          | 7 +++++++
 2 files changed, 10 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/Analysis/CtxProfAnalysis/flatten-prethinlink-requires-guid-metadata.ll

diff --git a/llvm/lib/Analysis/CtxProfAnalysis.cpp b/llvm/lib/Analysis/CtxProfAnalysis.cpp
index c4abec02e765a..f0255e303d062 100644
--- a/llvm/lib/Analysis/CtxProfAnalysis.cpp
+++ b/llvm/lib/Analysis/CtxProfAnalysis.cpp
@@ -441,7 +441,9 @@ GlobalValue::GUID AssignGUIDPass::getGUID(const Function &F) {
     return F.getGUID();
   }
   auto *MD = F.getMetadata(GUIDMetadataName);
-  assert(MD && "guid not found for defined function");
+  if (!MD)
+    reportFatalUsageError(
+        "this pass requires the GUID metadata to be available.");
   return cast<ConstantInt>(cast<ConstantAsMetadata>(MD->getOperand(0))
                                ->getValue()
                                ->stripPointerCasts())
diff --git a/llvm/test/Analysis/CtxProfAnalysis/flatten-prethinlink-requires-guid-metadata.ll b/llvm/test/Analysis/CtxProfAnalysis/flatten-prethinlink-requires-guid-metadata.ll
new file mode 100644
index 0000000000000..e234273bd7cc9
--- /dev/null
+++ b/llvm/test/Analysis/CtxProfAnalysis/flatten-prethinlink-requires-guid-metadata.ll
@@ -0,0 +1,7 @@
+; RUN: not opt -passes='ctx-prof-flatten-prethinlink' %s -disable-output 2>&1 | FileCheck %s
+
+; CHECK: LLVM ERROR: this pass requires the GUID metadata to be available.
+
+define void @test() {
+  ret void
+}