[llvm] [LLVM] Fix a bug in `Intrinsic::getFnAttributes` (PR #161248)

[Rahul Joshi via llvm-commits]

https://github.com/jurahul created https://github.com/llvm/llvm-project/pull/161248

When an intrinsic has no function attributes, the current code will hit an assert in `getIntrinsicFnAttributeSet`. Fix this by checking for the sentinel `NoFunctionAttrsID` value and returning an empty attribute set.

>From e8d3c388acd477199f8be4c39828abc362b438f9 Mon Sep 17 00:00:00 2001
From: Rahul Joshi <rjoshi at nvidia.com>
Date: Mon, 29 Sep 2025 10:56:37 -0700
Subject: [PATCH] [LLVM] Fix a bug in `Intrinsic::getFnAttributes`

When an intrinsic has no function attributes, the current code will
hit an assert in `getIntrinsicFnAttributeSet`. Fix this by checking
for the sentinel `NoFunctionAttrsID` value and returning an empty
attribute set.
---
 llvm/unittests/IR/IntrinsicsTest.cpp           | 8 ++++++++
 llvm/utils/TableGen/Basic/IntrinsicEmitter.cpp | 5 ++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/llvm/unittests/IR/IntrinsicsTest.cpp b/llvm/unittests/IR/IntrinsicsTest.cpp
index 49af83609d98c..cfd99ed542162 100644
--- a/llvm/unittests/IR/IntrinsicsTest.cpp
+++ b/llvm/unittests/IR/IntrinsicsTest.cpp
@@ -189,4 +189,12 @@ TEST_F(IntrinsicsTest, InstrProfInheritance) {
   }
 }
 
+// Check that getFnAttributes for intrinsics that do not have any function
+// attributes correcty returns an empty set.
+TEST(IntrinsicAttributes, TestGetFnAttributesBug) {
+  using namespace Intrinsic;
+  LLVMContext Context;
+  AttributeSet AS = getFnAttributes(Context, experimental_guard);
+  EXPECT_FALSE(AS.hasAttributes());
+}
 } // end namespace
diff --git a/llvm/utils/TableGen/Basic/IntrinsicEmitter.cpp b/llvm/utils/TableGen/Basic/IntrinsicEmitter.cpp
index 559868dd54efe..75dffb18fca5a 100644
--- a/llvm/utils/TableGen/Basic/IntrinsicEmitter.cpp
+++ b/llvm/utils/TableGen/Basic/IntrinsicEmitter.cpp
@@ -794,12 +794,15 @@ AttributeSet Intrinsic::getFnAttributes(LLVMContext &C, ID id) {{
   if (id == 0)
     return AttributeSet();
   auto [FnAttrID, _] = unpackID(IntrinsicsToAttributesMap[id - 1]);
+  if (FnAttrID == {})
+    return AttributeSet();
   return getIntrinsicFnAttributeSet(C, FnAttrID);
 }
 #endif // GET_INTRINSIC_ATTRIBUTES
 
 )",
-                UniqAttributesBitSize, MaxNumAttrs, NoFunctionAttrsID);
+                UniqAttributesBitSize, MaxNumAttrs, NoFunctionAttrsID,
+                NoFunctionAttrsID);
 }
 
 void IntrinsicEmitter::EmitIntrinsicToBuiltinMap(