Hello,
I think I've found a bug in the calling convention support for X86-64/
Win64. It doesn't correctly save and restore the XMM registers in
the function prolog/epilog. (The problem only exists on Win64, since
Linux and Mac OS use calling convention in which these registers are
volatile and not callee-saved.)
X86RegisterInfo::getCalleeSavedRegs() when called for a Win64 target
does return an array of registers which includes X86::XMM6 through
X86:XMM15.
However, the prolog/epilog code does not seem to be able handle saving
these registers correctly.
Firstly, in PEI::CalculateCalleeSavedRegisters() in CodeGen/
PrologEpilogInserter.cpp, the call to
Fn.getRegInfo().isPhysRegUsed(Reg) always seems to return true for the
all of the XMM registers if the Function being emitted makes any
function calls whatsoever, and so it tries to save all thecallee-saved
XMM registers even when none are actually used.
Further, the prolog/epilog emitter doesn't know how to correctly save
and restore the XMM registers on the stack. If outputting assembly,
it tries to emit "PUSH XMM6" and such; no such instruction exists,
and this does not assemble. If JIT'ting, it incorrectly emits PUSH
instructions for other registers which happen to share bit encodings
with the XMM registers (XMM6 becomes ESI, etc.)
Since there is no PUSH XMM* instruction, what needs to be done is to
adjust the stack pointer directly and then use MOVAPS to write/read
directly to the stack.
Is this already a known issue? Other than adding a custom calling
convention, all of my experience with LLVM has been as a client, so
I'm not sure how to proceed in fixing this, so if anyone could provide
pointers, I'd appreciate it.
-Craig
--
Craig Smith
National Instruments