[Mesa-dev] [PATCH v2 07/18] intel/compiler: fix brw_negate_immediate for 16-bit types

[Jason Ekstrand]

On Mon, Apr 30, 2018 at 7:18 AM, Iago Toral Quiroga <itoral at igalia.com>
wrote:

> From: Jose Maria Casanova Crespo <jmcasanova at igalia.com>
>
> From Intel Skylake PRM, vol 07, "Immediate" section (page 768):
>
> "For a word, unsigned word, or half-float immediate data,
> software must replicate the same 16-bit immediate value to both
> the lower word and the high word of the 32-bit immediate field
> in a GEN instruction."
>
> This patch implements float16 negate and fix the int16/uint16
> negate that wasn't taking into account the replication in lower
> and higher words.
>

Since this fixes a bug, do we want to split it in two and send the bug-fix
to stable?


> v2: Integer cases are different to Float cases. (Jason Ekstrand)
>     Included reference to PRM (Jose Maria Casanova)
> ---
>  src/intel/compiler/brw_shader.cpp | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/src/intel/compiler/brw_shader.cpp b/src/intel/compiler/brw_
> shader.cpp
> index 9cdf9fcb23..76dd1173fa 100644
> --- a/src/intel/compiler/brw_shader.cpp
> +++ b/src/intel/compiler/brw_shader.cpp
> @@ -580,8 +580,13 @@ brw_negate_immediate(enum brw_reg_type type, struct
> brw_reg *reg)
>        reg->d = -reg->d;
>        return true;
>     case BRW_REGISTER_TYPE_W:
> -   case BRW_REGISTER_TYPE_UW:
> -      reg->d = -(int16_t)reg->ud;
> +   case BRW_REGISTER_TYPE_UW: {
> +      uint16_t value = -(int16_t)reg->ud;
> +      reg->ud = value | value << 16;
>

You're shifting an explicitly 16-bit value by 16.  I think you want to cast
to uint32_t.


> +      return true;
> +   }
> +   case BRW_REGISTER_TYPE_HF:
> +      reg->ud ^= 0x80008000;
>        return true;
>     case BRW_REGISTER_TYPE_F:
>        reg->f = -reg->f;
> @@ -602,8 +607,6 @@ brw_negate_immediate(enum brw_reg_type type, struct
> brw_reg *reg)
>     case BRW_REGISTER_TYPE_UV:
>     case BRW_REGISTER_TYPE_V:
>        assert(!"unimplemented: negate UV/V immediate");
> -   case BRW_REGISTER_TYPE_HF:
> -      assert(!"unimplemented: negate HF immediate");
>     case BRW_REGISTER_TYPE_NF:
>        unreachable("no NF immediates");
>     }
> --
> 2.14.1
>
>
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