Segher Boessenkool <seg...@kernel.crashing.org> writes:
For things that do mftb with high frequency, maybe you should
also add a
builtin that does just an mftb, i.e. returns a 32-bit result
on 32-
bit
implementations.
Are you thinking in a function that returns only the TBL?
On 32-bit, just TBL; on 64-bit, the whole TB (there is no
machine
instruction to read just TBL on 64-bit, so it doesn't make much
sense to have it return a 32-bit number).
OK.
+(define_insn "get_timebase_ppc32"
+ [(set (match_operand:DI 0 "gpc_reg_operand" "=r")
+ (unspec_volatile:DI [(const_int 0)] UNSPECV_GETTB))
+ (clobber (match_scratch:SI 1 "=r"))]
+ "TARGET_POWERPC && !TARGET_POWERPC64"
+{
+ return "mftbu %0\;"
+ "mftb %L0\;"
+ "mftbu %1\;"
+ "cmpw %0,%1\;"
+ "bne- $-16";
+})
This only works for WORDS_BIG_ENDIAN.
Yes.
Do you mean you are fixing it? :-)
Yes. At least I'll try to. :-)
Does mftb work on all supported assemblers? The machine
instruction
is phased out, but some assemblers translate it to mfspr.
According to the Power ISA 2.06 they should translate it to
mfspr.
Yes, I realised that later.
But then a binary compiled with an assembler that emits mfspr
for mftb
will not run on POWER3 or 601. I don't know what to do about
that;
maybe just document it.
We can easily fix this at runtime, which isn't the case here.
Thanks again,
--
Tulio Magno
