From f1dcc7976a17f4da7235d05dbe8adbf18d323d7d Mon Sep 17 00:00:00 2001 From: Jason Ekstrand Date: Thu, 5 May 2016 16:38:25 -0700 Subject: [PATCH] i965: Stop splitting fma() prior to optimization According to the GLSL spec, if the user uses the fma() intrinsic to generate a precise-consumed value, and you have it in your hardware, you shouldn't split it. For a while now, we've been splitting all ffma's up-front and then planned to fuse them later which isn't valid. Correctly handling the GLSL behaviour fixes rendering corruptions in Tomb Raider. The only reason why doing this possibly helped before was for ARB programs which is handled by the previous commit. Shader-db results on Haswell: total instructions in shared programs: 7560300 -> 7561510 (0.02%) instructions in affected programs: 56265 -> 57475 (2.15%) helped: 86 HURT: 291 The only shaders in the database that are affected are from "Shadow of Mordor" which is the first app in our database to use fma(). We could, at some point in the future, split inexact ffma opcodes which would fix the shader-db regressions since Shadow of Mordor doesn't ues precise. However, this fixes a bug now and and the shader-db impact is fairly small. Reported-by: Kenneth Graunke Cc: "11.1 11.2" Reviewed-by: Kenneth Graunke --- src/mesa/drivers/dri/i965/brw_compiler.c | 5 ----- 1 file changed, 5 deletions(-) diff --git a/src/mesa/drivers/dri/i965/brw_compiler.c b/src/mesa/drivers/dri/i965/brw_compiler.c index eda0f6fa328..7c1b7e4327b 100644 --- a/src/mesa/drivers/dri/i965/brw_compiler.c +++ b/src/mesa/drivers/dri/i965/brw_compiler.c @@ -68,11 +68,6 @@ shader_perf_log_mesa(void *data, const char *fmt, ...) } #define COMMON_OPTIONS \ - /* In order to help allow for better CSE at the NIR level we tell NIR to \ - * split all ffma instructions during opt_algebraic and we then re-combine \ - * them as a later step. \ - */ \ - .lower_ffma = true, \ .lower_sub = true, \ .lower_fdiv = true, \ .lower_scmp = true, \ -- 2.30.2