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

[Manuel Jacob]

ping

On 2014-07-02 23:54, Manuel Jacob wrote:
> 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
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