[LLVMdev] [llvm-commits] [PATCH] fast-math patches!

[Michael Ilseman]

On Nov 15, 2012, at 8:07 PM, Joe Abbey <joe.abbey at gmail.com> wrote:

> Michael, 
> 
> Overall the code looks good.
> 
> 80-cols:
> 
> 2046           FMF.UnsafeAlgebra   = 0 != (Record[OpNum] & (1 << bitc::FMF_UNSAFE_ALGEBRA));
> 2047           FMF.NoNaNs          = 0 != (Record[OpNum] & (1 << bitc::FMF_NO_NANS));
> 2048           FMF.NoInfs          = 0 != (Record[OpNum] & (1 << bitc::FMF_NO_INFS));
> 2049           FMF.NoSignedZeros   = 0 != (Record[OpNum] & (1 << bitc::FMF_NO_SIGNED_ZEROS));
> 2050           FMF.AllowReciprocal = 0 != (Record[OpNum] & (1 << bitc::FMF_ALLOW_RECIPROCAL));
> 
> I found some more in BitcodeReader::ParseConstants(), which I'll scrub after this commits.
> 
> Will there be a // fmul N 1, x ==> x?  perhaps a // fadd N S 0, x ==> x?  as well as other arithmetic identities?
> 

Yes, that is the intent. You can see more examples in the original RFC. For you specific examples:

> fmul N 1, x ==> x


I think that the 'N' (now spelled 'nnan') flag isn't relevant to the optimization, as NaN * 1 ==> NaN.

>  fadd N S 0, x ==> x


Again, 'N' shouldn't apply. I don't think 'S' ('nsz') is needed here either, but it would be if it was x - 0 ==> x.

> Cheers,
> 
> Joe
> 
> 
> On Nov 15, 2012, at 9:54 PM, Michael Ilseman <milseman at apple.com> wrote:
> 
>> Another round of improved patches, and a patch for documentation changes to LangRef.
>>  * Make comments more up to date
>>  * Use 'arcp' instead of 'ar'
>>  * Use logical ||
>> 
>> Still based off of r168110
>> 
>> <0001-Fast-math-flags-added-to-FPMathOperator.patch>
>> <0002-Fast-math-interfaces-for-Instructions.patch>
>> <0003-Fast-math-flags-for-LLVM-IR-parsing-and-printing.patch>
>> <0004-Fast-math-flags-for-the-bitcode.patch>
>> <0005-Fast-math-test-case-for-bitcode-and-textual-reading-.patch>
>> <0006-Fast-math-optimization-fold-multiply-by-zero.patch>
>> <0007-Fast-math-test-for-SimplifyInstruction-fold-multiply.patch>
>> <0008-Fast-math-flags-documentation-added-to-LangRef.patch>

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