[LLVMdev] Possible bug in x86 code generation for fastcall on gnu/linux

[Mark Shannon]

Hi,

When compiling this function:

__attribute__((fastcall)) int f(int x, int y) {
    return 0;
}

llvm 2.3 produces the following x86 assembler (with directives removed):

f:
	xorl	%eax, %eax
	ret	$4

Where as GCC (version 4.2.3 (Ubuntu 4.2.3-2ubuntu7)) produces:

f:
	xorl	%eax, %eax
	ret

Note the difference in ret.

Functions calling a fastcall function in llvm adjust the stack by 4 to compensate for the above in llvm generated code,
whereas GCC generated function do not, since they do they need to.

Mark.


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