[IR] Do not set none for function uwtable

[caojoshua]

This avoids the pitfall where we set the uwtable to none:

func.setUWTableKind(llvm::UWTableKind::None)

Attribute::getAsString() would see an unknown attribute and fail an assertion. In this patch, we assert that we do not see a None uwtable kind.

This also skips the check of UWTableKind::Async. It is dominated by the check of UWTableKind::Default, which has the same enum value (nfc).

[llvmbot]

@llvm/pr-subscribers-llvm-ir

Author: Joshua Cao (caojoshua)

Changes

This avoids the pitfall where we set the uwtable to none:

func.setUWTableKind(llvm::UWTableKind::None)

Attribute::getAsString() would see an unknown attribute and fail an assertion. In this patch, we assert that we do not see a None uwtable kind.

This also skips the check of UWTableKind::Async. It is dominated by the check of UWTableKind::Default, which has the same enum value (nfc).

---

Full diff: https://github.com/llvm/llvm-project/pull/93387.diff

3 Files Affected:

• (modified) llvm/include/llvm/IR/Function.h (+2-1)
• (modified) llvm/lib/CodeGen/MachineOutliner.cpp (+1-2)
• (modified) llvm/lib/IR/Attributes.cpp (+3-7)

diff --git a/llvm/include/llvm/IR/Function.h b/llvm/include/llvm/IR/Function.h
index cb514cde95b51..be745a0083cb7 100644
--- a/llvm/include/llvm/IR/Function.h
+++ b/llvm/include/llvm/IR/Function.h
@@ -654,7 +654,8 @@ class LLVM_EXTERNAL_VISIBILITY Function : public GlobalObject,
     return getUWTableKind() != UWTableKind::None;
   }
   void setUWTableKind(UWTableKind K) {
-    addFnAttr(Attribute::getWithUWTableKind(getContext(), K));
+    if (K != UWTableKind::None)
+      addFnAttr(Attribute::getWithUWTableKind(getContext(), K));
   }
   /// True if this function needs an unwind table.
   bool needsUnwindTableEntry() const {
diff --git a/llvm/lib/CodeGen/MachineOutliner.cpp b/llvm/lib/CodeGen/MachineOutliner.cpp
index dc2f5ef15206e..f174dd857def0 100644
--- a/llvm/lib/CodeGen/MachineOutliner.cpp
+++ b/llvm/lib/CodeGen/MachineOutliner.cpp
@@ -717,8 +717,7 @@ MachineFunction *MachineOutliner::createOutlinedFunction(
       [](UWTableKind K, const outliner::Candidate &C) {
         return std::max(K, C.getMF()->getFunction().getUWTableKind());
       });
-  if (UW != UWTableKind::None)
-    F->setUWTableKind(UW);
+  F->setUWTableKind(UW);
 
   BasicBlock *EntryBB = BasicBlock::Create(C, "entry", F);
   IRBuilder<> Builder(EntryBB);
diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index c8d6bdd423878..cc3a2ceb6de84 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -526,13 +526,9 @@ std::string Attribute::getAsString(bool InAttrGrp) const {
 
   if (hasAttribute(Attribute::UWTable)) {
     UWTableKind Kind = getUWTableKind();
-    if (Kind != UWTableKind::None) {
-      return Kind == UWTableKind::Default
-                 ? "uwtable"
-                 : ("uwtable(" +
-                    Twine(Kind == UWTableKind::Sync ? "sync" : "async") + ")")
-                       .str();
-    }
+    assert(Kind != UWTableKind::None &&
+           "uwtable attribute should not be none");
+    return Kind == UWTableKind::Default ? "uwtable" : "uwtable(sync)";
   }
 
   if (hasAttribute(Attribute::AllocKind)) {

[caojoshua]

IREE sets a None uwtable kind. With a IREE build with assertions, when printing LLVM IR with --print-after-all, I get

Unknown attribute
UNREACHABLE executed at /home/josh/src/iree/third_party/llvm-project/llvm/lib/IR/Attributes.cpp:643!

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[caojoshua]

I'm not sure if the Kind is always expected to not be UWTableKind::None, but the current code seems to make that assumption. If it is None, we fall through to the llvm_unreachable at the bottom of the function.

[nikic]

LGTM