[llvm-commits] [llvm-gcc-4.2] r99670 - /llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp

[Bill Wendling]

Author: void
Date: Fri Mar 26 18:40:55 2010
New Revision: 99670

URL: http://llvm.org/viewvc/llvm-project?rev=99670&view=rev
Log:
A clean-up needs to be marked as a clean-up. It could cause problems in the
libunwind library otherwise. Take this program for an example:

int main() {
    try {
        throw new std::exception();
    } catch (std::exception *e) {
        throw e;
    }
}

At the re-throw, the libunwind expects the state to be in a clean-up
state. However, because we generate catch-alls in our code, the personality
returns the wrong state the libunwind, which then barfs.

Marking that re-throw as a clean-up puts libunwind into the correct state.

There is other code here, though. If we mark clean-ups as clean-ups, then it
could break when inlining through an 'invoke' instruction. You will get a
situation like this:

bb:
  %ehptr = eh.exception()
  %sel = eh.selector(%ehptr, @per, 0);

...

bb2:
  invoke _Unwind_Resume_or_Rethrow(%ehptr) %normal unwind to %lpad

lpad:
  ...

The unwinder will see the %sel call as a clean-up and, if it doesn't have a
catch further up the call stack, it will skip running it. But there *is* another
catch up the stack -- the catch for the %lpad. However, we can't see that. This
is fixed in code-gen, where we detect this situation, and convert the "clean-up"
selector call into a "catch-all" selector call. This gives us the correct
semantics.

Modified:
    llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp

Modified: llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp?rev=99670&r1=99669&r2=99670&view=diff
==============================================================================
--- llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp (original)
+++ llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp Fri Mar 26 18:40:55 2010
@@ -2089,6 +2089,9 @@
     // Add selections for each handler.
     foreach_reachable_handler(i, false, AddHandler, &Handlers);
 
+    bool HasCleanup = false;
+    static Value *CatchAll = 0;
+
     for (std::vector<struct eh_region *>::iterator I = Handlers.begin(),
          E = Handlers.end(); I != E; ++I) {
       struct eh_region *region = *I;
@@ -2115,9 +2118,16 @@
 
         if (!TypeList) {
           // Catch-all - push a null pointer.
-          Args.push_back(
-            Constant::getNullValue(Type::getInt8PtrTy(Context))
-          );
+          if (!CatchAll) {
+            Constant *Init =
+              Constant::getNullValue(Type::getInt8PtrTy(Context));
+
+            CatchAll = new GlobalVariable(*TheModule, Init->getType(), true,
+                                          GlobalVariable::LinkOnceAnyLinkage,
+                                          Init, ".llvm.eh.catch.all.value");
+          }
+
+          Args.push_back(CatchAll);
         } else {
           // Add the type infos.
           for (; TypeList; TypeList = TREE_CHAIN(TypeList)) {
@@ -2125,30 +2135,43 @@
             Args.push_back(Emit(TType, 0));
           }
         }
+      } else {
+        // Cleanup.
+        HasCleanup = true;
       }
     }
 
     if (can_throw_external_1(i, false)) {
-      // Some exceptions from this region may not be caught by any handler.
-      // Since invokes are required to branch to the unwind label no matter
-      // what exception is being unwound, append a catch-all.
-
-      // The representation of a catch-all is language specific.
-      Value *CatchAll;
-      if (USING_SJLJ_EXCEPTIONS || !lang_eh_catch_all) {
-        // Use a "cleanup" - this should be good enough for most languages.
-        CatchAll = ConstantInt::get(Type::getInt32Ty(Context), 0);
+      if (HasCleanup && Args.size() == 2) {
+        Args.push_back(ConstantInt::get(Type::getInt32Ty(Context), 0));
       } else {
-        tree catch_all_type = lang_eh_catch_all();
-        if (catch_all_type == NULL_TREE)
-          // Use a C++ style null catch-all object.
-          CatchAll = Constant::getNullValue(
-                                    Type::getInt8PtrTy(Context));
-        else
-          // This language has a type that catches all others.
-          CatchAll = Emit(catch_all_type, 0);
+        // Some exceptions from this region may not be caught by any handler.
+        // Since invokes are required to branch to the unwind label no matter
+        // what exception is being unwound, append a catch-all.
+
+        // The representation of a catch-all is language specific.
+        if (USING_SJLJ_EXCEPTIONS || !lang_eh_catch_all) {
+          // Use a "cleanup" - this should be good enough for most languages.
+          Args.push_back(ConstantInt::get(Type::getInt32Ty(Context), 0));
+        } else {
+          if (!CatchAll) {
+            Constant *Init = 0;
+            tree catch_all_type = lang_eh_catch_all();
+            if (catch_all_type == NULL_TREE)
+              // Use a C++ style null catch-all object.
+              Init = Constant::getNullValue(Type::getInt8PtrTy(Context));
+            else
+              // This language has a type that catches all others.
+              Init = cast<Constant>(Emit(catch_all_type, 0));
+
+            CatchAll = new GlobalVariable(*TheModule, Init->getType(), true,
+                                          GlobalVariable::PrivateLinkage,
+                                          Init, ".llvm.eh.catch.all.value");
+          }
+
+          Args.push_back(CatchAll);
+        }
       }
-      Args.push_back(CatchAll);
     }
 
     // Emit the selector call.