[ORC] Fix handling of casts in llvm.global_ctors.

Removes a bogus dyn_cast_or_null that was breaking cast-expression handling when
parsing llvm.global_ctors.

The intent of this code was to identify Functions nested within cast
expressions, but the offending dyn_cast_or_null was actually blocking that:
Since a function is not a cast expression, we would set FuncC to null and break
the loop without finding the Function. The cast was not necessary either:
Functions are already Constants, and we didn't need to do anything
ConstantExpr-specific with FuncC, so we could just drop the cast.

Thanks to Jonas Hahnfeld for tracking this down.

http://llvm.org/PR54797

llvm/lib/ExecutionEngine/Orc/ExecutionUtils.cpp

@@ -62,7 +62,7 @@ CtorDtorIterator::Element CtorDtorIterator::operator*() const {
       break;
     } else if (ConstantExpr *CE = dyn_cast_or_null<ConstantExpr>(FuncC)) {
       if (CE->isCast())
-        FuncC = dyn_cast_or_null<ConstantExpr>(CE->getOperand(0));
+        FuncC = CE->getOperand(0);
       else
         break;
     } else {

llvm/test/ExecutionEngine/Orc/global-ctor-with-cast.ll

@@ -0,0 +1,19 @@
+; Test that global constructors behind casts are run
+;
+; RUN: lli -jit-kind=orc %s | FileCheck %s
+;
+; CHECK: constructor
+
+declare i32 @puts(i8*)
+
+@.str = private constant [12 x i8] c"constructor\00"
+@llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 1, void ()* bitcast (i32 ()* @constructor to void ()*), i8* null }]
+
+define internal i32 @constructor() #0 {
+  %call = tail call i32 @puts(i8* getelementptr inbounds ([12 x i8], [12 x i8]* @.str, i64 0, i64 0))
+  ret i32 0
+}
+
+define i32 @main()  {
+  ret i32 0
+}