<div dir="ltr"> <div class="gmail_extra"> <div class="gmail_quote">On Fri, Oct 23, 2015 at 10:55 AM, Eduardo Lima Mitev <<a href="mailto:elima@igalia.com" target="_blank">elima@igalia.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">When both fadd and fmul instructions have at least one operand that is a constant and it is only used once, the total number of instructions can be reduced from 3 (1 ffma + 2 load_const) to 2 (1 fmul + 1 fadd); because the constants will be progagated as immediate operands of fmul and fadd. This patch detects these situations and prevents fusing fmul+fadd into ffma. Shader-db results on i965 Haswell: total instructions in shared programs: 6235835 -> 6225895 (-0.16%) instructions in affected programs: 1124094 -> 1114154 (-0.88%) total loops in shared programs: 1979 -> 1979 (0.00%) helped: 7612 HURT: 843 GAINED: 4 LOST: 0 --- .../drivers/dri/i965/brw_nir_opt_peephole_ffma.c | 31 ++++++++++++++++++++++ 1 file changed, 31 insertions(+) diff --git a/src/mesa/drivers/dri/i965/brw_nir_opt_peephole_ffma.c b/src/mesa/drivers/dri/i965/brw_nir_opt_peephole_ffma.c index a8448e7..c7fc15a 100644 --- a/src/mesa/drivers/dri/i965/brw_nir_opt_peephole_ffma.c +++ b/src/mesa/drivers/dri/i965/brw_nir_opt_peephole_ffma.c @@ -133,6 +133,28 @@ get_mul_for_src(nir_alu_src *src, int num_components, return alu; } +/** + * Given a list of (at least two) nir_alu_src's, tells if any of them is a + * constant value and is used only once. + */ +static bool +any_alu_src_is_a_constant(nir_alu_src srcs[]) +{ + for (unsigned i = 0; i < 2; i++) { + if (srcs[i].src.ssa->parent_instr->type == nir_instr_type_load_const) { + nir_load_const_instr *load_const = + nir_instr_as_load_const (srcs[i].src.ssa->parent_instr); + + if (list_is_single(&load_const->def.uses) && + list_empty(&load_const->def.if_uses)) { + return true; + } + } + } + + return false; +} + </blockquote><div> </div><div>The comment above this functions reads "Given a list of (at least two) nir_alu_src's...", but the function checks exactly two. Was it your intention to support lists with size > 2? </div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> static bool brw_nir_opt_peephole_ffma_block(nir_block *block, void *void_state) { @@ -183,6 +205,15 @@ brw_nir_opt_peephole_ffma_block(nir_block *block, void *void_state) mul_src[0] = mul->src[0].src.ssa; mul_src[1] = mul->src[1].src.ssa; + /* If any of the operands of the fmul and any of the fadd is a constant, + * we bypass because it will be more efficient as the constants will be + * propagated as operands, potentially saving two load_const instructions. + */ + if (any_alu_src_is_a_constant(mul->src) && + any_alu_src_is_a_constant(add->src)) { + continue; + } + if (abs) { for (unsigned i = 0; i < 2; i++) { nir_alu_instr *abs = nir_alu_instr_create(state->mem_ctx, -- 2.5.3 _______________________________________________ mesa-dev mailing list <a href="mailto:mesa-dev@lists.freedesktop.org">mesa-dev@lists.freedesktop.org</a> <a href="http://lists.freedesktop.org/mailman/listinfo/mesa-dev" rel="noreferrer" target="_blank">http://lists.freedesktop.org/mailman/listinfo/mesa-dev</a> </blockquote></div> </div></div>