Re: Ping Patch: PR target/24879: SSE3 intrinsic bug

[Ian Lance Taylor <ian at airs dot com>]

"H. J. Lu" <hjl@lucon.org> writes:

> On Tue, May 02, 2006 at 02:49:13PM -0700, Ian Lance Taylor wrote:
> > "H. J. Lu" <hjl@lucon.org> writes:
> > 
> > > On Mon, May 01, 2006 at 11:41:16PM -0700, Ian Lance Taylor wrote:
> > 
> > > > I don't understand why the definition of __builtin_ia32_monitor and
> > > > __builtin_ia32_mwait change for 64-bit mode.  As I understand it, they
> > > > always take two SImode values.  So it seems to me that the type should
> > > > be the same for both, whether you are in 32-bit mode or 64-bit mode.
> > > > 
> > > 
> > > The IA32 SDM isn't very clear for this. I have checked with our chip
> > > people.  The 64bit version should be
> > > 
> > > 	mwait  %rax,%rcx
> > > 	monitor %eax,%rcx,%rdx
> > 
> > Yes, I believe I understand that.  But my understanding is that
> > despite the use of 64-bit registers for the final two arguments of
> > each instruction, only the low order 32-bits are significant.
> > Therefore, it seems to me that the builtin function (not the
> > instruction; the builtin function) should always use a 32-bit
> > parameter type, whether you are doing a 32-bit build or a 64-bit
> > build.  That is the part of your patch that I am questioning.
> 
> My understand is the builtin function will match the instruction. The
> intrinsic will make sure that the proper bits are used. That is how
> x86 builtin function/intrinsic works.

The builtin function is the builtin function, and the MD file insn is
the MD file insn.  While they are normally similar, they are logically
distinct and there is no special relationship between them.  This is
obvious if you think about builtin functions like __builtin_memcpy.
The function causes certain insns to be emitted, but there is no
connection closer than that.

In this case, since only 32-bit values are valid, it seems to me that
the builtin function should logically accept only 32-bit values in
both 32-bit and 64-bit mode.  Since the 64-bit mode instruction
requires a 64-bit register, the 32-bit value should be zero-extended
into a 64-bit register before emitting the instruction.

Ian