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intel/fs: Fix constant propagation into 32x16 integer multiplication

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Don't copy propagate the constant in situations like

    mov(8)          g8<1>D          0x7fffffffD
    mul(8)          g16<1>D         g8<8,8,1>D      g15<16,8,2>W

On platforms that only have a 32x16 multiplier, this will result in
lowering the multiply to

    mul(8)          g15<1>D         g14<8,8,1>D     0xffffUW
    mul(8)          g16<1>D         g14<8,8,1>D     0x7fffUW
    add(8)          g15.1<2>UW      g15.1<16,8,2>UW g16<16,8,2>UW

On Gfx8 and Gfx9, which have the full 32x32 multiplier, it results in

    mul(8)          g16<1>D         g15<16,8,2>W    0x7fffffffD

Volume 2a of the Skylake PRM says:

    When multiplying a DW and any lower precision integer, the
    DW operand must on src0.

See also https://gitlab.freedesktop.org/mesa/crucible/-/merge_requests/104.

Previous to INTEL_shader_integer_functions2 (in Vulkan or OpenGL), I
don't think it would be possible to create a situation where this could
occur.  I discovered this via some optimizations that can determine that
the non-constant source must be able to fit in 16-bits.  The case listed
above came from piglit's "ext_transform_feedback-order arrays points"
with those optimizations in place.

No shader-db or fossil-db changes on any Intel platform.

Fixes: de6c0f8487 ("intel/fs: Implement support for NIR opcodes for INTEL_shader_integer_functions2")
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17718>
(cherry picked from commit db20412168)
This commit is contained in:
Ian Romanick
2022-02-08 13:26:13 -08:00
committed by Dylan Baker
parent 3f1fe4b6bd
commit b7a7e78ade
2 changed files with 28 additions and 1 deletions
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2
.pick_status.json
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@@ -184,7 +184,7 @@
"description": "intel/fs: Fix constant propagation into 32x16 integer multiplication",
"nominated": true,
"nomination_type": 1,
"resolution": 0,
"resolution": 1,
"main_sha": null,
"because_sha": "de6c0f848797d26d28223bcad25da03654461874"
},

27
src/intel/compiler/brw_fs_copy_propagation.cpp
View File

@@ -836,6 +836,33 @@ fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
inst->src[i] = val;
progress = true;
} else if (i == 0 && inst->src[1].file != IMM) {
/* Don't copy propagate the constant in situations like
*
* mov(8) g8<1>D 0x7fffffffD
* mul(8) g16<1>D g8<8,8,1>D g15<16,8,2>W
*
* On platforms that only have a 32x16 multiplier, this will
* result in lowering the multiply to
*
* mul(8) g15<1>D g14<8,8,1>D 0xffffUW
* mul(8) g16<1>D g14<8,8,1>D 0x7fffUW
* add(8) g15.1<2>UW g15.1<16,8,2>UW g16<16,8,2>UW
*
* On Gfx8 and Gfx9, which have the full 32x32 multiplier, it
* results in
*
* mul(8) g16<1>D g15<16,8,2>W 0x7fffffffD
*
* Volume 2a of the Skylake PRM says:
*
* When multiplying a DW and any lower precision integer, the
* DW operand must on src0.
*/
if (inst->opcode == BRW_OPCODE_MUL &&
type_sz(inst->src[1].type) < 4 &&
type_sz(val.type) == 4)
break;
/* Fit this constant in by commuting the operands.
* Exception: we can't do this for 32-bit integer MUL/MACH
* because it's asymmetric.