Using MSVC _ftol2 runtime function for fptoui on Win32

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#1

Hi Joe & Michael,

In rev. 151382 you have changed the fptoui implementation of the x86 codegen for win32.

Before the change fptoui was lowered to

flds 16(%esp)

fisttpll 8(%esp)

movl 8(%esp), %eax

After the change fptoui is lowered to

flds 40(%esp)

calll _ftol2

Please note that the assumption that _ftol2 doesn’t modify ECX isn’t true on sandybridge platform.

Could you share with me the reasons behind this change? Did you get better performance after this change?

Thanks,

Asaf

#2

"fisttp" is only available with SSE3 or later, and before that change, if
SSE3 was unavailable, legalization would lower fptoui and fptosi to a
libgcc/compiler-rt call that does not exist on Win32, so the change was
necessary for compatibility with MSVC. If SSE3 is enabled, it should use
'fisttp', and if _ftol2 clobbers ECX, the pseudo-instruction for it can be
fixed to reflect that. Those would both be good things to fix.

-Joe