Segmentation fault with GEP and null address

[hberntsen]

When you add the following code to llvm-general/test/LLVM/General/Test/Instructions.hs in the list of tests, the tests will crash with a segmentation fault:

          ("GEP2",
            GetElementPtr {
                inBounds = False,
                address = ConstantOperand $ C.Null (IntegerType 32),
                indices = [ConstantOperand $ C.Int 32 1],
                metadata = []
           },
           "getelementptr i32* null, i32 1"),

(I am using version v3.4.2.2 with LLVM 3.4 on Ubuntu 14.04) I wanted to try the trick described at http://nondot.org/sabre/LLVMNotes/SizeOf-OffsetOf-VariableSizedStructs.txt to let llvm calculate sizes in my compiler. I tested with GHC 7.8.2 and 7.6.3 and both give a segmentation fault for this test.

gdb tells:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff6a046af in llvm::CompositeType::getTypeAtIndex(llvm::Value const*) () from /usr/lib/x86_64-linux-gnu/libLLVM-3.4.so.1

When using (ArrayType 2 (PointerType (IntegerType 32) (AddrSpace 0)):

Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f9ca0a7ec44 in llvm::PointerType::get(llvm::Type*, unsigned int) () from /usr/lib/x86_64-linux-gnu/libLLVM-3.4.so.1

[bscarlet]

The type used with C.Null needs to be a pointer type - e.g. C.Null (PointerType (IntegerType 32) 0). You might consider using a build of llvm with asserts turned on, at least for development. It'll give you informative messages in some cases like this, rather than just dying.

[hberntsen]

Thanks for you quick response. That indeed solves my problem. I did not expect a segmentation fault with the wrong AST, apparently that is how LLVM works. Makes sense though, all the assertions decrease compiling speed.