[Exception Handling] Unwind tables are required for all functions that have an EH personality.

[stefanp]

Summary

This patch is for defect:
https://bugs.llvm.org/show_bug.cgi?id=32611

Functions may require unwind tables even if they are marked with the attribute nounwind. Any function with an EH personality may require an unwind table.

[rnk]

Needs a test, but it's the right idea. You should be able to do an x86_64 test and ppc64. I'm also surprised it doesn't require other test changes.

[stefanp]

Sorry about that. I should have added the test cases earlier.

[rnk]

lgtm

[hfinkel]

Does this mean that we can remove that previously-discussed x86 logic in Clang?

[stefanp]

I'm not 100% sure if we can remove the default option -funwind-tables for x86.
I know that using -funwind-tables prevents (or hides) this issue but it may be required for another reason that this fix does not cover. I don't actually know what the initial intention was when that default was added.
I think that someone on the x86 side would be a better judge of this.

[hfinkel]

In D50987#1214336, @stefanp wrote:

I'm not 100% sure if we can remove the default option -funwind-tables for x86.
I know that using -funwind-tables prevents (or hides) this issue but it may be required for another reason that this fix does not cover. I don't actually know what the initial intention was when that default was added.
I think that someone on the x86 side would be a better judge of this.

@craig.topper , do you know?

include/llvm/IR/Function.h

bool hasUWTable() const {
     return hasFnAttribute(Attribute::UWTable);
   }
   void setHasUWTable() {
     addFnAttr(Attribute::UWTable);
   }
 
   /// True if this function needs an unwind table.
   bool needsUnwindTableEntry() const {
-    return hasUWTable() || !doesNotThrow();
+    return hasUWTable() || !doesNotThrow() || hasPersonalityFn();
   }
 
   /// Determine if the function returns a structure through first
   /// or second pointer argument.
   bool hasStructRetAttr() const {
     return AttributeSets.hasParamAttribute(0, Attribute::StructRet) ||
            AttributeSets.hasParamAttribute(1, Attribute::StructRet);
   }