Re-apply the fix on DwarfEHPrepare and add a test (#2)

* Ad -run-twice to dwarf-eh-prepare.ll

* In DwarfEHPrepare, after all passes are run, RewindFunction may be a dangling
pointer to a dead function. To make sure it's valid, doFinalization nullptrs
RewindFunction just like the constructor and so it will be found on next run.

llvm-svn: 217737

Co-authored-by: Yaron Keren <[email protected]>

https://reviews.llvm.org/D110979

Author: tkf

llvm/lib/CodeGen/DwarfEHPrepare.cpp

@@ -302,6 +302,11 @@ class DwarfEHPrepareLegacyPass : public FunctionPass {
     return prepareDwarfEH(OptLevel, RewindFunction, F, TLI, DT, TTI);
   }
 
+  bool doFinalization(Module &M) override {
+    RewindFunction = nullptr;
+    return false;
+  }
+
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<TargetPassConfig>();
     AU.addRequired<TargetTransformInfoWrapperPass>();

llvm/test/CodeGen/X86/dwarf-eh-prepare.ll

@@ -1,4 +1,4 @@
-; RUN: opt -mtriple=x86_64-linux-gnu -dwarfehprepare -simplifycfg-require-and-preserve-domtree=1 < %s -S | FileCheck %s
+; RUN: opt -mtriple=x86_64-linux-gnu -dwarfehprepare -simplifycfg-require-and-preserve-domtree=1 -run-twice < %s -S | FileCheck %s
 
 ; Check basic functionality of IR-to-IR DWARF EH preparation. This should
 ; eliminate resumes. This pass requires a TargetMachine, so we put it under X86