[llvm-commits] [llvm] r113996 - in /llvm/trunk: include/llvm/MC/MCInst.h lib/Target/ARM/ARMMCInstLower.cpp lib/Target/ARM/AsmPrinter/ARMInstPrinter.cpp

[Jim Grosbach]

On Sep 15, 2010, at 1:19 PM, Stephen Canon wrote:

> On Sep 15, 2010, at 1:05 PM, Dale Johannesen wrote:
> 
>> On Sep 15, 2010, at 11:47 AMPDT, Jim Grosbach wrote:
>> 
>>> Author: grosbach
>>> Date: Wed Sep 15 13:47:08 2010
>>> New Revision: 113996
>>> 
>>> URL: http://llvm.org/viewvc/llvm-project?rev=113996&view=rev
>>> Log:
>>> Add support for floating point immediates to MC instruction printing. ARM
>>> VFP instructions use it for loading some constants, so implement that
>>> handling.
>>> 
>>> Not thrilled with adding a member to MCOperand, but not sure there's much of
>>> a better option that's not pretty fragile (like putting a double in the
>>> union instead and just assuming that's good enough). Suggestions welcome...
>> 
>> This doesn't seem to handle NaNs and infinities.  Also, I wonder whether you're guaranteed to get enough precision to represent the value accurately with << (printf does not guarantee this).  Will the assembler take a hex format?  That would be better.
> 
> Fortunately, ARM doesn't support NaN or infinity as FP immediates; the allowed FP immediates of the form:
> 
> 	+/-(1 + m/16)*2^e
> 
> where m is an integer in [0,15] and e is an integer in [-3,4].
> 
> I agree with Dale that the hex format would be ideal if the assembler will swallow it.  Leave conversions between binary and decimal out of it.

I wish I could, but unified syntax requires the immediate be a floating point immediate. Pre-unified syntax it was a binary 8 bit immediate as encoded into the instruction. I wish it hadn't been changed, but...

-Jim