[Mesa-dev] [PATCH] radeonsi: don't preload constants at the beginning of shaders

[Marek Olšák]

From: Marek Olšák <marek.olsak at amd.com>

LLVM can CSE the loads, thus we can always re-load constants before each
use. The decrease in SGPR spilling is huge.

The best improvements are the dumbest ones.

26011 shaders in 14651 tests
Totals:
SGPRS: 1453346 -> 1251920 (-13.86 %)
VGPRS: 742576 -> 728421 (-1.91 %)
Spilled SGPRs: 52298 -> 16644 (-68.17 %)
Spilled VGPRs: 397 -> 369 (-7.05 %)
Scratch VGPRs: 1372 -> 1344 (-2.04 %) dwords per thread
Code Size: 36136488 -> 36001064 (-0.37 %) bytes
LDS: 767 -> 767 (0.00 %) blocks
Max Waves: 219315 -> 222221 (1.33 %)
---
 src/gallium/drivers/radeonsi/si_shader.c | 30 +++++++++++-------------------
 1 file changed, 11 insertions(+), 19 deletions(-)

diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c
index 0b7de18..08e3cee 100644
--- a/src/gallium/drivers/radeonsi/si_shader.c
+++ b/src/gallium/drivers/radeonsi/si_shader.c
@@ -1874,26 +1874,33 @@ static LLVMValueRef fetch_constant(
 		for (chan = 0; chan < TGSI_NUM_CHANNELS; ++chan)
 			values[chan] = fetch_constant(bld_base, reg, type, chan);
 
 		return lp_build_gather_values(bld_base->base.gallivm, values, 4);
 	}
 
 	buf = reg->Register.Dimension ? reg->Dimension.Index : 0;
 	idx = reg->Register.Index * 4 + swizzle;
 
 	if (!reg->Register.Indirect && !reg->Dimension.Indirect) {
+		LLVMValueRef c0, c1;
+
+		c0 = buffer_load_const(ctx, ctx->const_buffers[buf],
+				       LLVMConstInt(ctx->i32, idx * 4, 0));
+
 		if (!tgsi_type_is_64bit(type))
-			return bitcast(bld_base, type, ctx->constants[buf][idx]);
+			return bitcast(bld_base, type, c0);
 		else {
+			c1 = buffer_load_const(ctx, ctx->const_buffers[buf],
+					       LLVMConstInt(ctx->i32,
+							    (idx + 1) * 4, 0));
 			return radeon_llvm_emit_fetch_64bit(bld_base, type,
-							    ctx->constants[buf][idx],
-							    ctx->constants[buf][idx + 1]);
+							    c0, c1);
 		}
 	}
 
 	if (reg->Register.Dimension && reg->Dimension.Indirect) {
 		LLVMValueRef ptr = LLVMGetParam(ctx->radeon_bld.main_fn, SI_PARAM_CONST_BUFFERS);
 		LLVMValueRef index;
 		index = get_bounded_indirect_index(ctx, &reg->DimIndirect,
 						   reg->Dimension.Index,
 						   SI_NUM_CONST_BUFFERS);
 		bufp = build_indexed_load_const(ctx, ptr, index);
@@ -5789,39 +5796,26 @@ static void create_function(struct si_shader_context *ctx)
 
 static void preload_constants(struct si_shader_context *ctx)
 {
 	struct lp_build_tgsi_context *bld_base = &ctx->radeon_bld.soa.bld_base;
 	struct gallivm_state *gallivm = bld_base->base.gallivm;
 	const struct tgsi_shader_info *info = bld_base->info;
 	unsigned buf;
 	LLVMValueRef ptr = LLVMGetParam(ctx->radeon_bld.main_fn, SI_PARAM_CONST_BUFFERS);
 
 	for (buf = 0; buf < SI_NUM_CONST_BUFFERS; buf++) {
-		unsigned i, num_const = info->const_file_max[buf] + 1;
-
-		if (num_const == 0)
+		if (info->const_file_max[buf] == -1)
 			continue;
 
-		/* Allocate space for the constant values */
-		ctx->constants[buf] = CALLOC(num_const * 4, sizeof(LLVMValueRef));
-
 		/* Load the resource descriptor */
 		ctx->const_buffers[buf] =
 			build_indexed_load_const(ctx, ptr, lp_build_const_int32(gallivm, buf));
-
-		/* Load the constants, we rely on the code sinking to do the rest */
-		for (i = 0; i < num_const * 4; ++i) {
-			ctx->constants[buf][i] =
-				buffer_load_const(ctx,
-					ctx->const_buffers[buf],
-					lp_build_const_int32(gallivm, i * 4));
-		}
 	}
 }
 
 static void preload_shader_buffers(struct si_shader_context *ctx)
 {
 	struct gallivm_state *gallivm = &ctx->radeon_bld.gallivm;
 	LLVMValueRef ptr = LLVMGetParam(ctx->radeon_bld.main_fn, SI_PARAM_SHADER_BUFFERS);
 	int buf, maxbuf;
 
 	maxbuf = MIN2(ctx->shader->selector->info.file_max[TGSI_FILE_BUFFER],
@@ -6898,22 +6892,20 @@ int si_compile_tgsi_shader(struct si_screen *sscreen,
 		ctx.shader = shader->gs_copy_shader;
 		if ((r = si_generate_gs_copy_shader(sscreen, &ctx,
 						    shader, debug))) {
 			free(shader->gs_copy_shader);
 			shader->gs_copy_shader = NULL;
 			goto out;
 		}
 	}
 
 out:
-	for (int i = 0; i < SI_NUM_CONST_BUFFERS; i++)
-		FREE(ctx.constants[i]);
 	return r;
 }
 
 /**
  * Create, compile and return a shader part (prolog or epilog).
  *
  * \param sscreen	screen
  * \param list		list of shader parts of the same category
  * \param key		shader part key
  * \param tm		LLVM target machine
-- 
2.7.4