Re: [PATCH, rs6000] Fix HTM __builtin_ttest rtl expansion

[David Edelsohn <dje dot gcc at gmail dot com>]

On Tue, May 20, 2014 at 3:28 PM, Peter Bergner <bergner@vnet.ibm.com> wrote:
> The following patch fixes a semi-latent bug for the HTM pattern used with
> the __builtin_ttest() builtin.  This is supposed to expand to a tabortwci.
> instruction which sets cr0 and then some code that copies the cr0 value
> into a gpr and then shifts and masks it into the lowest 2 bits in the gpr.
>
> With newish -mcpu targets, we generate a "mfocrf rX,128" to copy the cr0
> value into bits 32-35 of the gpr.  However, in some cases, we will instead
> generate a "mfcr rX" instruction, which copies all 8 CR fields into the
> gpr, with cr0 again being in bits 32-35.  The difference is that the
> mfocrf instruction seems to duplicate the 4-bit CR field in the gpr,
> so bits 36-39 are a duplicate of bits 32-35.  The error in the ttest
> pattern is that we only shift the value down 24 bits.  This "works"
> when a mfocrf copied the cr0 into the rgeister due the duplicated CR
> field, but is wrong when a mfcr instruction is used.
>
> The following passed bootstrap and regtesting on powerpc64-linux.
> Ok for trunk?  Is this also ok for the 4.9 and 4.8 branches once
> my bootstraps and regtesting is done there?
>
> Peter
>
>
> gcc/
>         * config/rs6000/htm.md (ttest): Use correct shift value to get CR0.
>
> gcc/testsuite/
>         * gcc.target/powerpc/htm-ttest.c: New test.

Okay.

Thanks, David