[PATCH 2/2] Revert "Don't remove a landing pad if the invoke requires a table entry."

[Björn Steinbrink]

The reverted change was an attempt to fix handling of functions marked
`uwtable` to force creation of unwind table entries by disallowing to
replace `invoke` with `call` for those functions. Unfortunately, this
was wrong in two ways. First, it forced creation of unwind tables even
if all entries were for empty cleanups that just resumed the unwinding,
which is unnecessary. Additionally, it had no effect on functions marked
`nounwind` in addition to `uwtable`, still leaving them without unwind
table entries.

My previous commit enforces creation of unwind table entries for all
functions marked `uwtable`, even when the `invoke` -> `call` replacement
is performed, so let's revert this.
---
 lib/Transforms/Utils/SimplifyCFG.cpp         | 20 ++------
 test/Transforms/SimplifyCFG/trivial-throw.ll | 77 ----------------------------
 2 files changed, 3 insertions(+), 94 deletions(-)
 delete mode 100644 test/Transforms/SimplifyCFG/trivial-throw.ll

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index effc08e..9c23d77 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2868,20 +2868,9 @@ bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
       return false;
 
   // Turn all invokes that unwind here into calls and delete the basic block.
-  bool InvokeRequiresTableEntry = false;
-  bool Changed = false;
   for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
     InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
-
-    if (II->hasFnAttr(Attribute::UWTable)) {
-      // Don't remove an `invoke' instruction if the ABI requires an entry into
-      // the table.
-      InvokeRequiresTableEntry = true;
-      continue;
-    }
-
     SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
-
     // Insert a call instruction before the invoke.
     CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
     Call->takeName(II);
@@ -2901,14 +2890,11 @@ bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
 
     // Finally, delete the invoke instruction!
     II->eraseFromParent();
-    Changed = true;
   }
 
-  if (!InvokeRequiresTableEntry)
-    // The landingpad is now unreachable.  Zap it.
-    BB->eraseFromParent();
-
-  return Changed;
+  // The landingpad is now unreachable.  Zap it.
+  BB->eraseFromParent();
+  return true;
 }
 
 bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
diff --git a/test/Transforms/SimplifyCFG/trivial-throw.ll b/test/Transforms/SimplifyCFG/trivial-throw.ll
deleted file mode 100644
index ca2b569..0000000
--- a/test/Transforms/SimplifyCFG/trivial-throw.ll
+++ /dev/null
@@ -1,77 +0,0 @@
-; RUN: opt -simplifycfg -S < %s | FileCheck %s
-; <rdar://problem/13360379>
-
- at _ZTVN10__cxxabiv117__class_type_infoE = external global i8*
- at _ZTS13TestException = linkonce_odr constant [16 x i8] c"13TestException\00"
- at _ZTI13TestException = linkonce_odr unnamed_addr constant { i8*, i8* } { i8* bitcast (i8** getelementptr inbounds (i8** @_ZTVN10__cxxabiv117__class_type_infoE, i64 2) to i8*), i8* getelementptr inbounds ([16 x i8]* @_ZTS13TestException, i32 0, i32 0) }
-
-define void @throw(i32 %n) #0 {
-entry:
-  %exception = call i8* @__cxa_allocate_exception(i64 1) #4
-  call void @__cxa_throw(i8* %exception, i8* bitcast ({ i8*, i8* }* @_ZTI13TestException to i8*), i8* null) #2
-  unreachable
-}
-
-define void @func() #0 {
-entry:
-; CHECK: func()
-; CHECK: invoke void @throw
-; CHECK-NOT: call void @throw
-  invoke void @throw(i32 42) #0
-          to label %exit unwind label %lpad
-
-lpad:
-  %tmp0 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*)
-          cleanup
-  resume { i8*, i32 } %tmp0
-
-exit:
-  invoke void @abort() #2
-          to label %invoke.cont unwind label %lpad1
-
-invoke.cont:
-  unreachable
-
-lpad1:
-  %tmp1 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*)
-          catch i8* bitcast ({ i8*, i8* }* @_ZTI13TestException to i8*)
-  %tmp2 = extractvalue { i8*, i32 } %tmp1, 1
-  %tmp3 = call i32 @llvm.eh.typeid.for(i8* bitcast ({ i8*, i8* }* @_ZTI13TestException to i8*)) #4
-  %matches = icmp eq i32 %tmp2, %tmp3
-  br i1 %matches, label %catch, label %eh.resume
-
-catch:
-  ret void
-
-eh.resume:
-  resume { i8*, i32 } %tmp1
-}
-
-define linkonce_odr hidden void @__clang_call_terminate(i8*) #1 {
-  %2 = call i8* @__cxa_begin_catch(i8* %0) #4
-  call void @_ZSt9terminatev() #5
-  unreachable
-}
-
-declare void @abort() #2
-
-declare i32 @llvm.eh.typeid.for(i8*) #3
-
-declare void @__cxa_end_catch()
-
-declare i8* @__cxa_allocate_exception(i64)
-
-declare i32 @__gxx_personality_v0(...)
-
-declare void @__cxa_throw(i8*, i8*, i8*)
-
-declare i8* @__cxa_begin_catch(i8*)
-
-declare void @_ZSt9terminatev()
-
-attributes #0 = { ssp uwtable }
-attributes #1 = { noinline noreturn nounwind }
-attributes #2 = { noreturn }
-attributes #3 = { nounwind readnone }
-attributes #4 = { nounwind }
-attributes #5 = { noreturn nounwind }
-- 
1.9.0.rc3