[LLVMdev] Address arithmetic result is incorrectly zero-extended (X86)

[Manuel Jacob]

Hi,

I'm trying to fix bug 12802 [1].  The problem is that the C statement 
"return ((long)&x) - 600000000;" (where x is a variable defined at file 
scope) generates the code "movl $x-600000000, %eax" while it should be 
"movq $x-600000000, %rax".  This means that the result is incorrectly 
zero-extended instead of sign-extended, causing an error with some 
linkers and incorrect results with some other linkers.  It seems like 
the wrong instruction is selected in X86DAGToDAGISel::SelectMOV64Imm32.  
I tried to add an extra check that makes the function return false if 
the offset of the GlobalAddressSDNode is negative, but this causes the 
instruction selector to not select an instruction at all (it fails with 
a "Cannot select" error).  Any help is appreciated.

-Manuel

[1] http://llvm.org/bugs/show_bug.cgi?id=12802