[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);
   }

test/CodeGen/PowerPC/uwtables.ll

+; RUN: llc -mcpu=pwr9 -mtriple=powerpc64le-unknown-unknown \
+; RUN:   -verify-machineinstrs -ppc-asm-full-reg-names \
+; RUN:   -ppc-vsr-nums-as-vr < %s | FileCheck %s
+; RUN: llc -mcpu=pwr8 -mtriple=powerpc64le-unknown-unknown \
+; RUN:   -verify-machineinstrs -ppc-asm-full-reg-names \
+; RUN:   -ppc-vsr-nums-as-vr < %s | FileCheck %s
+; RUN: llc -mtriple=powerpc64-unknown-unknown \
+; RUN:   -verify-machineinstrs -ppc-asm-full-reg-names \
+; RUN:   -ppc-vsr-nums-as-vr < %s | FileCheck %s
+
+
+@_ZTIi = external constant i8*
+
+; Function is marked as nounwind but it still throws with __cxa_throw and
+; calls __cxa_call_unexpected.
+; Need to make sure that we do not only have a debug frame.
+; Function Attrs: noreturn nounwind
+define void @_Z4funcv() local_unnamed_addr #0 personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+entry:
+  %exception = tail call i8* @__cxa_allocate_exception(i64 4)
+  %0 = bitcast i8* %exception to i32*
+  store i32 100, i32* %0, align 16
+  invoke void @__cxa_throw(i8* %exception, i8* bitcast (i8** @_ZTIi to i8*), i8* null)
+          to label %unreachable unwind label %lpad
+
+lpad:                                             ; preds = %entry
+  %1 = landingpad { i8*, i32 }
+          filter [0 x i8*] zeroinitializer
+  %2 = extractvalue { i8*, i32 } %1, 0
+  tail call void @__cxa_call_unexpected(i8* %2)
+  unreachable
+
+unreachable:                                      ; preds = %entry
+  unreachable
+; CHECK-LABEL: _Z4funcv
+; CHECK-NOT: .debug_frame
+; CHECK: .cfi_personality
+; CHECK: .cfi_endproc
+}
+
+declare i8* @__cxa_allocate_exception(i64) local_unnamed_addr
+
+declare void @__cxa_throw(i8*, i8*, i8*) local_unnamed_addr
+
+declare i32 @__gxx_personality_v0(...)
+
+declare void @__cxa_call_unexpected(i8*) local_unnamed_addr
+
+
+attributes #0 = { noreturn nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="ppc64le" "target-features"="+altivec,+bpermd,+crypto,+direct-move,+extdiv,+htm,+power8-vector,+vsx,-power9-vector,-qpx" "unsafe-fp-math"="false" "use-soft-float"="false" }
+

test/CodeGen/X86/uwtables.ll

+; RUN: llc -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
+
+
+@_ZTIi = external constant i8*
+
+; Function is marked as nounwind but it still throws with __cxa_throw and
+; calls __cxa_call_unexpected.
+; Need to make sure that we do not only have a debug frame.
+; Function Attrs: noreturn nounwind
+define void @_Z4funcv() local_unnamed_addr #0 personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+entry:
+  %exception = tail call i8* @__cxa_allocate_exception(i64 4)
+  %0 = bitcast i8* %exception to i32*
+  store i32 100, i32* %0, align 16
+  invoke void @__cxa_throw(i8* %exception, i8* bitcast (i8** @_ZTIi to i8*), i8* null)
+          to label %unreachable unwind label %lpad
+
+lpad:                                             ; preds = %entry
+  %1 = landingpad { i8*, i32 }
+          filter [0 x i8*] zeroinitializer
+  %2 = extractvalue { i8*, i32 } %1, 0
+  tail call void @__cxa_call_unexpected(i8* %2)
+  unreachable
+
+unreachable:                                      ; preds = %entry
+  unreachable
+; CHECK-LABEL: _Z4funcv
+; CHECK-NOT: .debug_frame
+; CHECK: .cfi_personality
+; CHECK: .cfi_endproc
+}
+
+declare i8* @__cxa_allocate_exception(i64) local_unnamed_addr
+
+declare void @__cxa_throw(i8*, i8*, i8*) local_unnamed_addr
+
+declare i32 @__gxx_personality_v0(...)
+
+declare void @__cxa_call_unexpected(i8*) local_unnamed_addr
+
+
+attributes #0 = { noreturn nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="ppc64le" "target-features"="+altivec,+bpermd,+crypto,+direct-move,+extdiv,+htm,+power8-vector,+vsx,-power9-vector,-qpx" "unsafe-fp-math"="false" "use-soft-float"="false" }
+

test/CodeGen/X86/x86-shrink-wrap-unwind.ll

 ; happen.
 ; PR36513
 ;
 ; CHECK-LABEL: with_nounwind:
 ; Prologue
 ; CHECK: push
 ;
 ; Jump to throw_exception:
+; CHECK-NEXT: .cfi_def_cfa_offset
 ; CHECK-NEXT: testb $1, %dil
 ; CHECK-NEXT: jne [[THROW_LABEL:LBB[0-9_]+]]
 ; Else return exit
 ; CHECK: popq
 ; CHECK-NEXT: retq
 ;
 ; CHECK-NEXT: [[THROW_LABEL]]:
 ; CHECK: callq  _throw_exception