From 284b563fb0689f8c51aae45ad9e331ba4b776ddf Mon Sep 17 00:00:00 2001 From: Ian Romanick Date: Wed, 13 Jun 2018 12:32:27 -0700 Subject: [PATCH] i965/fs: Optimize OR with 0 into a MOV MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit fs_visitor::set_gs_stream_control_data_bits generates some code like "control_data_bits | stream_id << ((2 * (vertex_count - 1)) % 32)" as part of EmitVertex. The first time this (dynamically) occurs in the shader, control_data_bits is zero. Many times we can determine this statically and various optimizations will collaborate to make one of the OR operands literal zero. Converting the OR to a MOV usually allows it to be copy-propagated away. However, this does not happen in at least some shaders (in the assembly output of shaders/closed/UnrealEngine4/EffectsCaveDemo/301.shader_test, search for shl). All of the affected shaders are geometry shaders. Broadwell and Skylake had similar results. (Skylake shown) total instructions in shared programs: 14375452 -> 14375413 (<.01%) instructions in affected programs: 6422 -> 6383 (-0.61%) helped: 39 HURT: 0 helped stats (abs) min: 1 max: 1 x̄: 1.00 x̃: 1 helped stats (rel) min: 0.14% max: 2.56% x̄: 1.91% x̃: 2.56% 95% mean confidence interval for instructions value: -1.00 -1.00 95% mean confidence interval for instructions %-change: -2.26% -1.57% Instructions are helped. total cycles in shared programs: 531981179 -> 531980555 (<.01%) cycles in affected programs: 27493 -> 26869 (-2.27%) helped: 39 HURT: 0 helped stats (abs) min: 16 max: 16 x̄: 16.00 x̃: 16 helped stats (rel) min: 0.60% max: 7.92% x̄: 5.94% x̃: 7.92% 95% mean confidence interval for cycles value: -16.00 -16.00 95% mean confidence interval for cycles %-change: -6.98% -4.90% Cycles are helped. No changes on earlier platforms. Signed-off-by: Ian Romanick --- src/intel/compiler/brw_fs.cpp | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp index d67c0a41922..d836b268629 100644 --- a/src/intel/compiler/brw_fs.cpp +++ b/src/intel/compiler/brw_fs.cpp @@ -2448,7 +2448,8 @@ fs_visitor::opt_algebraic() } break; case BRW_OPCODE_OR: - if (inst->src[0].equals(inst->src[1])) { + if (inst->src[0].equals(inst->src[1]) || + inst->src[1].is_zero()) { inst->opcode = BRW_OPCODE_MOV; inst->src[1] = reg_undef; progress = true; -- 2.30.2