[Mesa-dev] [PATCH 1/5] i965: Define virtual instruction to calculate the high 32 bits of a multiply.

[Ilia Mirkin]

On Wed, Aug 5, 2015 at 1:52 PM, Francisco Jerez <currojerez at riseup.net> wrote:
> This instruction will translate to the MUL/MACH sequence that computes
> the high 32-bits of the result of a 64-bit multiply.  Before Gen8

Unlike with 32x32 -> low 32, you need to specify if it's a signed or
unsigned multiply. s32 x s32 -> high 32 takes a bunch of extra effort
if you're splitting the multiply up into 32-bit chunks.

By the way, ARB_gpu_shader5 introduced umulExtended and imulExtended
which produce the full 64-bit result for both variants... I would have
assumed this would already be somehow handled in i965.

> integer operations that used the accumulator were limited to 8-wide,
> but the SIMD lowering pass can easily be hooked up to sidestep this
> limitation, we just need a virtual opcode to represent the MUL/MACH
> sequence in the IR.
> ---
>  src/mesa/drivers/dri/i965/brw_defines.h                 | 5 +++++
>  src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp   | 1 +
>  src/mesa/drivers/dri/i965/brw_fs_cse.cpp                | 1 +
>  src/mesa/drivers/dri/i965/brw_shader.cpp                | 4 ++++
>  src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp | 1 +
>  src/mesa/drivers/dri/i965/brw_vec4_cse.cpp              | 1 +
>  6 files changed, 13 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
> index f595366..9c232c4 100644
> --- a/src/mesa/drivers/dri/i965/brw_defines.h
> +++ b/src/mesa/drivers/dri/i965/brw_defines.h
> @@ -1214,6 +1214,11 @@ enum opcode {
>      * GLSL barrier()
>      */
>     SHADER_OPCODE_BARRIER,
> +
> +   /**
> +    * Calculate the high 32-bits of a 32x32 multiply.
> +    */
> +   SHADER_OPCODE_MULH,
>  };
>
>  enum brw_urb_write_flags {
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> index 3940158..a4fb21d 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> @@ -534,6 +534,7 @@ fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
>
>        case BRW_OPCODE_MACH:
>        case BRW_OPCODE_MUL:
> +      case SHADER_OPCODE_MULH:
>        case BRW_OPCODE_ADD:
>        case BRW_OPCODE_OR:
>        case BRW_OPCODE_AND:
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
> index a123ff2..c7628dc 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
> @@ -61,6 +61,7 @@ is_expression(const fs_visitor *v, const fs_inst *const inst)
>     case BRW_OPCODE_CMPN:
>     case BRW_OPCODE_ADD:
>     case BRW_OPCODE_MUL:
> +   case SHADER_OPCODE_MULH:
>     case BRW_OPCODE_FRC:
>     case BRW_OPCODE_RNDU:
>     case BRW_OPCODE_RNDD:
> diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp b/src/mesa/drivers/dri/i965/brw_shader.cpp
> index 819e4f2..bccf8d6 100644
> --- a/src/mesa/drivers/dri/i965/brw_shader.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
> @@ -778,6 +778,8 @@ brw_instruction_name(enum opcode op)
>        return "cs_terminate";
>     case SHADER_OPCODE_BARRIER:
>        return "barrier";
> +   case SHADER_OPCODE_MULH:
> +      return "mulh";
>     }
>
>     unreachable("not reached");
> @@ -996,6 +998,7 @@ backend_instruction::is_commutative() const
>     case BRW_OPCODE_XOR:
>     case BRW_OPCODE_ADD:
>     case BRW_OPCODE_MUL:
> +   case SHADER_OPCODE_MULH:
>        return true;
>     case BRW_OPCODE_SEL:
>        /* MIN and MAX are commutative. */
> @@ -1103,6 +1106,7 @@ backend_instruction::can_do_saturate() const
>     case BRW_OPCODE_MATH:
>     case BRW_OPCODE_MOV:
>     case BRW_OPCODE_MUL:
> +   case SHADER_OPCODE_MULH:
>     case BRW_OPCODE_PLN:
>     case BRW_OPCODE_RNDD:
>     case BRW_OPCODE_RNDE:
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
> index 2d9afa8..5a15eb8 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
> @@ -179,6 +179,7 @@ try_constant_propagate(const struct brw_device_info *devinfo,
>
>     case BRW_OPCODE_MACH:
>     case BRW_OPCODE_MUL:
> +   case SHADER_OPCODE_MULH:
>     case BRW_OPCODE_ADD:
>     case BRW_OPCODE_OR:
>     case BRW_OPCODE_AND:
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp b/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp
> index c9fe0ce..5a277f7 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp
> @@ -62,6 +62,7 @@ is_expression(const vec4_instruction *const inst)
>     case BRW_OPCODE_CMPN:
>     case BRW_OPCODE_ADD:
>     case BRW_OPCODE_MUL:
> +   case SHADER_OPCODE_MULH:
>     case BRW_OPCODE_FRC:
>     case BRW_OPCODE_RNDU:
>     case BRW_OPCODE_RNDD:
> --
> 2.4.6
>
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