[CodeGen] Add "noreturn" attirbute to _Unwind_Resume

[ebrevnov]

Summary

Currently 'resume' is lowered to _Unwind_Resume with out "noreturn" attribute. Semantically _Unwind_Resume library call is expected to never return and should be marked as such. Though I didn't find any changes in behavior of existing tests there will be a difference once https://reviews.llvm.org/D79485 lands.

I was not able to come up with the test case anything better than just checking for presence of "noreturn" attribute. Please let me know if there is a better way to test the change.

[xbolva00]

Please add a test

[ebrevnov]

Added test case.

[ebrevnov]

Updated test case due to https://reviews.llvm.org/D79485 has landed.

[xbolva00]

noreturn makes sense here

[thakis]

Looks like this breaks tests on arm64-apple-macos: http://45.33.8.238/macm1/761/step_10.txt

Please take a look.

[ebrevnov]

Thanks for letting me know. Looking now...

[xbolva00]

llvm/test/CodeGen/Generic/dwarf_eh_resume.ll

2

Linux x86-64 triple to fix test on apple?

[ebrevnov]

Yes. Please review proposed fix https://reviews.llvm.org/D93803. Evgeniy

llvm/lib/CodeGen/DwarfEHPrepare.cpp

if (ResumesLeft == 1) {
     BasicBlock *UnwindBB = RI->getParent();
     Value *ExnObj = GetExceptionObject(RI);
 
     // Call the _Unwind_Resume function.
     CallInst *CI = CallInst::Create(RewindFunction, ExnObj, "", UnwindBB);
     CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
 
     // We never expect _Unwind_Resume to return.
+    CI->setDoesNotReturn();
     new UnreachableInst(Ctx, UnwindBB);
     return true;
   }
 
   BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
   PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesLeft,
                                 "exn.obj", UnwindBB);
 
for (ResumeInst *RI : Resumes) {
     ++NumResumesLowered;
   }
 
   // Call the function.
   CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
   CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
 
   // We never expect _Unwind_Resume to return.
+  CI->setDoesNotReturn();
   new UnreachableInst(Ctx, UnwindBB);
   return true;
 }
 
 bool DwarfEHPrepare::runOnFunction(Function &Fn) {
   const TargetMachine &TM =
       getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
   DT = OptLevel != CodeGenOpt::None
       ? &getAnalysis<DominatorTreeWrapperPass>().getDomTree() : nullptr;
   TLI = TM.getSubtargetImpl(Fn)->getTargetLowering();
   bool Changed = InsertUnwindResumeCalls(Fn);
   DT = nullptr;
   TLI = nullptr;
   return Changed;
 }

llvm/test/CodeGen/Generic/dwarf_eh_resume.ll

+; RUN: llc %s -stop-after=irtranslator -o - | FileCheck %s
+
+declare i32 @hoge(...)
+
+; Check that 'resume' is lowered to _Unwind_Resume which marked as 'noreturn'
+define void @pluto() align 2 personality i8* bitcast (i32 (...)* @hoge to i8*) {
+;CHECK: call void @_Unwind_Resume(i8* %exn.obj) [[A:#.*]]
+;CHECK: attributes [[A]] = { noreturn }
+bb:
+  invoke void @spam()
+          to label %bb1 unwind label %bb2
+
+bb1:                                              ; preds = %bb
+  ret void
+
+bb2:                                              ; preds = %bb
+  %tmp = landingpad { i8*, i32 }
+          cleanup
+  resume { i8*, i32 } %tmp
+
+}
+
+declare void @spam()