[Mesa-dev] [PATCH RFC] radeonsi: Disable IEEE_MODE.

[Eric Engestrom]

On Monday, 2018-03-05 14:07:24 -0500, Jan Vesely wrote:
> On Mon, 2018-03-05 at 10:04 +0000, Eric Engestrom wrote:
> > On Saturday, 2018-03-03 18:35:02 -0500, Jan Vesely wrote:
> > > Neither GL nor CL nor SPIRV needs the IEEE handling of sNaNs.
> > > 
> > > Signed-off-by: Jan Vesely <jan.vesely at rutgers.edu>
> > > ---
> > > This is the 3rd way to handle broken fmin/fmax in clover CL.
> > > It can be worked around in libclc (to not use
> > > llvm.fminnum/llvm.fmaxnum)[0]
> > > LLVM can be patched to not use IEEE_MODE[1]
> > > Or it can be fixed in the config reg in mesa.
> > > 
> > > The third option is arguably the worst (changes semantics of compiled
> > > code), but since the first two efforts have been stalled for months.
> > > Here's the third one.
> > > 
> > > Jan
> > > 
> > > [0] http://lists.llvm.org/pipermail/libclc-dev/2017-November/thread.html#2692
> > > [1] https://reviews.llvm.org/D40514
> > > 
> > > 
> > >  src/gallium/drivers/radeonsi/si_compute.c | 8 ++++++++
> > >  src/gallium/drivers/radeonsi/si_shader.c  | 6 +++++-
> > >  2 files changed, 13 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/src/gallium/drivers/radeonsi/si_compute.c b/src/gallium/drivers/radeonsi/si_compute.c
> > > index 41927988cf..d0fcba485b 100644
> > > --- a/src/gallium/drivers/radeonsi/si_compute.c
> > > +++ b/src/gallium/drivers/radeonsi/si_compute.c
> > > @@ -70,6 +70,10 @@ static void code_object_to_config(const amd_kernel_code_t *code_object,
> > >  				  struct si_shader_config *out_config) {
> > >  
> > >  	uint32_t rsrc1 = code_object->compute_pgm_resource_registers;
> > > +	/* Disable IEEE mode. IEEE_MODE determines sNaN handling by fmin/fmax
> > > +	 * instructions. Nothing wants the IEEE rules here.
> > > +	 * Ideally LLVM would not emit this configuration. */
> > > +	rsrc1 &= C_00B848_IEEE_MODE;
> > 
> > I don't know anything about this code, but this bit op looks odd to me;
> > I would expect to see either:
> > 	rsrc1 &= ~C_00B848_IEEE_MODE;
> 
> C_00B848_IEEE_MODE is defined as 0xFF7FFFFF, so it's already bit-
> negated.

Alright, looks reasonable then :)

> 
> Jan
> 
> > or:
> > 	rsrc1 |= C_00B848_IEEE_MODE;
> > 
> > >  	uint32_t rsrc2 = code_object->compute_pgm_resource_registers >> 32;
> > >  	out_config->num_sgprs = code_object->wavefront_sgpr_count;
> > >  	out_config->num_vgprs = code_object->workitem_vgpr_count;
> > > @@ -137,6 +141,10 @@ static void si_create_compute_state_async(void *job, int thread_index)
> > >  			S_00B848_SGPRS((shader->config.num_sgprs - 1) / 8) |
> > >  			S_00B848_DX10_CLAMP(1) |
> > >  			S_00B848_FLOAT_MODE(shader->config.float_mode);
> > > +		/* Disable IEEE mode. IEEE_MODE determines sNaN handling by
> > > +		 * fmin/fmax instructions. Nothing wants the IEEE rules.
> > > +		 * Ideally LLVM would not emit this configuration. */
> > > +		shader->config.rsrc1 &= C_00B848_IEEE_MODE;
> > >  
> > >  		shader->config.rsrc2 =
> > >  			S_00B84C_USER_SGPR(user_sgprs) |
> > > diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c
> > > index 2a50b266f6..01bad71a4e 100644
> > > --- a/src/gallium/drivers/radeonsi/si_shader.c
> > > +++ b/src/gallium/drivers/radeonsi/si_shader.c
> > > @@ -5178,7 +5178,11 @@ void si_shader_binary_read_config(struct ac_shader_binary *binary,
> > >  			conf->num_sgprs = MAX2(conf->num_sgprs, (G_00B028_SGPRS(value) + 1) * 8);
> > >  			conf->num_vgprs = MAX2(conf->num_vgprs, (G_00B028_VGPRS(value) + 1) * 4);
> > >  			conf->float_mode =  G_00B028_FLOAT_MODE(value);
> > > -			conf->rsrc1 = value;
> > > +			/* Disable IEEE mode. IEEE_MODE determines sNaN
> > > +			 * handling by fmin/fmax instructions.
> > > +			 * Nothing wants the IEEE rules here.
> > > +			 * Ideally LLVM would not emit this configuration. */
> > > +			conf->rsrc1 = value & C_00B848_IEEE_MODE;
> > >  			break;
> > >  		case R_00B02C_SPI_SHADER_PGM_RSRC2_PS:
> > >  			conf->lds_size = MAX2(conf->lds_size, G_00B02C_EXTRA_LDS_SIZE(value));
> > > -- 
> > > 2.14.3
> > > 
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