[CodeGen] Don't assume that a landing pad exists in setMustKeepGlobalVariables

[mstorsjo]

Summary

This fixes crashes (PR30535) when building C++ code (with exceptions enabled) for ARM/Windows with optimizations enabled.

[mstorsjo]

Ping @qcolombet or anyone else familiar with GlobalMerge.cpp.

[hans]

+majnemer who knows about these things.

mstorsjo: Please turn the IR reproducer on the PR into a test case and add to the patch.

[mstorsjo]

Added a test based on the pretty minimal IR that shows the issue.

[majnemer]

lib/CodeGen/GlobalMerge.cpp

513–521

This seems wrong. We should add cases for catchswitch & cleanuppad.

[mstorsjo]

This seems to have been fixed differently in SVN r284633.

lib/CodeGen/GlobalMerge.cpp

void GlobalMerge::setMustKeepGlobalVariables(Module &M) {
   for (Module::iterator IFn = M.begin(), IEndFn = M.end(); IFn != IEndFn;
        ++IFn) {
     for (Function::iterator IBB = IFn->begin(), IEndBB = IFn->end();
          IBB != IEndBB; ++IBB) {
       // Follow the invoke link to find the landing pad instruction
       const InvokeInst *II = dyn_cast<InvokeInst>(IBB->getTerminator());
       if (!II) continue;
 
       const LandingPadInst *LPInst = II->getUnwindDest()->getLandingPadInst();
+      if (!LPInst) continue;
       // Look for globals in the clauses of the landing pad instruction
       for (unsigned Idx = 0, NumClauses = LPInst->getNumClauses();
            Idx != NumClauses; ++Idx)
         if (const GlobalVariable *GV =
             dyn_cast<GlobalVariable>(LPInst->getClause(Idx)
                                      ->stripPointerCasts()))
           MustKeepGlobalVariables.insert(GV);
     }
   }
 }
 
 bool GlobalMerge::doInitialization(Module &M) {
   if (!EnableGlobalMerge)
     return false;
 

test/CodeGen/ARM/Windows/exceptions-opt.ll

+; RUN: llc -mtriple thumbv7--windows-msvc -o - %s | FileCheck %s
+
+%struct.B = type { i8 }
+
+@"\01?x@@3UB@@A" = global %struct.B zeroinitializer, align 1
[e-mail]_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 65535, void ()* @_GLOBAL__sub_I_exceptions.cpp, i8* null }]
+
+declare arm_aapcs_vfpcc void @"\01?f@B@@QAAXXZ"(%struct.B*) local_unnamed_addr #0
+
+declare arm_aapcs_vfpcc i32 @__CxxFrameHandler3(...)
+
+define internal arm_aapcs_vfpcc void @_GLOBAL__sub_I_exceptions.cpp() #1 personality i32 (...)* @__CxxFrameHandler3 {
+  invoke arm_aapcs_vfpcc void @"\01?f@B@@QAAXXZ"(%struct.B* nonnull @"\01?x@@3UB@@A")
+          to label %5 unwind label %1
+
+; <label>:1:                                      ; preds = %0
+  %2 = catchswitch within none [label %3] unwind to caller
+
+; <label>:3:                                      ; preds = %1
+  %4 = catchpad within %2 [i8* null, i32 64, i8* null]
+  catchret from %4 to label %5
+
+; <label>:5:                                      ; preds = %0, %3
+  ret void
+}
+
+; Only check that building this doesn't crash.
+; CHECK-LABEL: exceptions