Null exports should only be needed when no other exports are
emitted. This removes a bunch of 'exp null off, off, off, off done vm'.

Affected games are Dota 2 and Wolfenstein 2, not sure if that
really helps, but code size is decreasing there.

Polaris10:
Totals from affected shaders:
SGPRS: 8216 -> 8216 (0.00 %)
VGPRS: 7072 -> 7072 (0.00 %)
Spilled SGPRs: 0 -> 0 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Code Size: 454968 -> 453896 (-0.24 %) bytes
Max Waves: 772 -> 772 (0.00 %)

Signed-off-by: Samuel Pitoiset <samuel.pitoi...@gmail.com>
---
 src/amd/common/ac_nir_to_llvm.c | 98 ++++++++++++++++++++++-------------------
 1 file changed, 52 insertions(+), 46 deletions(-)

diff --git a/src/amd/common/ac_nir_to_llvm.c b/src/amd/common/ac_nir_to_llvm.c
index ea51c3a54a..c370c80ec7 100644
--- a/src/amd/common/ac_nir_to_llvm.c
+++ b/src/amd/common/ac_nir_to_llvm.c
@@ -6484,67 +6484,73 @@ handle_tcs_outputs_post(struct radv_shader_context *ctx)
        write_tess_factors(ctx);
 }
 
-static bool
-si_export_mrt_color(struct radv_shader_context *ctx,
-                   LLVMValueRef *color, unsigned index, bool is_last,
-                   struct ac_export_args *args)
-{
-       /* Export */
-       si_llvm_init_export_args(ctx, color, 0xf,
-                                V_008DFC_SQ_EXP_MRT + index, args);
-
-       if (is_last) {
-               args->valid_mask = 1; /* whether the EXEC mask is valid */
-               args->done = 1; /* DONE bit */
-       } else if (!args->enabled_channels)
-               return false; /* unnecessary NULL export */
-
-       return true;
-}
+struct radv_ps_exports {
+       unsigned num;
+       struct ac_export_args args[10];
+};
 
 static void
 radv_export_mrt_z(struct radv_shader_context *ctx,
                  LLVMValueRef depth, LLVMValueRef stencil,
-                 LLVMValueRef samplemask)
+                 LLVMValueRef samplemask, struct radv_ps_exports *exp)
 {
        struct ac_export_args args;
 
        ac_export_mrt_z(&ctx->ac, depth, stencil, samplemask, &args);
 
-       ac_build_export(&ctx->ac, &args);
+       memcpy(&exp->args[exp->num++], &args, sizeof(args));
 }
 
 static void
 handle_fs_outputs_post(struct radv_shader_context *ctx)
 {
-       unsigned index = 0;
        LLVMValueRef depth = NULL, stencil = NULL, samplemask = NULL;
-       struct ac_export_args color_args[8];
+       struct radv_ps_exports exp = {};
+       struct ac_export_args args[8];
+       int last_color_export = -1;
+       int last_non_null = -1;
+       unsigned colors_written;
+
+       /* Find the last written color export. */
+       colors_written = ctx->output_mask >> FRAG_RESULT_DATA0;
+       if (!ctx->shader_info->info.ps.writes_z &&
+           !ctx->shader_info->info.ps.writes_stencil &&
+           !ctx->shader_info->info.ps.writes_sample_mask) {
+               last_color_export = util_last_bit(colors_written) - 1;
+       }
+
+       /* Get the export arguments, and find the last non-null color export. */
+       for (unsigned mrt = 0; mrt < 8; mrt++) {
+               unsigned index = mrt + FRAG_RESULT_DATA0;
+               LLVMValueRef color[4];
+
+               if (!(colors_written & (1 << mrt)))
+                       continue;
 
-       for (unsigned i = 0; i < AC_LLVM_MAX_OUTPUTS; ++i) {
-               LLVMValueRef values[4];
-               bool last = false;
+               for (unsigned chan = 0; chan < 4; chan++) {
+                       color[chan] =
+                               ac_to_float(&ctx->ac,
+                                           radv_load_output(ctx, index, chan));
+               }
 
-               if (!(ctx->output_mask & (1ull << i)))
-                       continue;
+               si_llvm_init_export_args(ctx, color, 0xf,
+                                        V_008DFC_SQ_EXP_MRT + mrt, &args[mrt]);
+               if (args[mrt].enabled_channels)
+                       last_non_null = mrt;
+       }
 
-               if (i < FRAG_RESULT_DATA0)
+       /* Emit all exports. */
+       for (unsigned mrt = 0; mrt < 8; mrt++) {
+               if (!(colors_written & (1 << mrt)))
                        continue;
 
-               for (unsigned j = 0; j < 4; j++)
-                       values[j] = ac_to_float(&ctx->ac,
-                                               radv_load_output(ctx, i, j));
+               if (last_color_export != -1 && last_non_null == mrt) {
+                       args[mrt].valid_mask = 1; /* whether the EXEC mask is 
valid */
+                       args[mrt].done = 1; /* DONE bit */
+               } else if (!args[mrt].enabled_channels)
+                       continue; /* unnecessary NULL export */
 
-               if (!ctx->shader_info->info.ps.writes_z &&
-                   !ctx->shader_info->info.ps.writes_stencil &&
-                   !ctx->shader_info->info.ps.writes_sample_mask)
-                       last = ctx->output_mask <= ((1ull << (i + 1)) - 1);
-
-               bool ret = si_export_mrt_color(ctx, values,
-                                              i - FRAG_RESULT_DATA0,
-                                              last, &color_args[index]);
-               if (ret)
-                       index++;
+               memcpy(&exp.args[exp.num++], &args[mrt], sizeof(args[mrt]));
        }
 
        /* Process depth, stencil, samplemask. */
@@ -6561,14 +6567,14 @@ handle_fs_outputs_post(struct radv_shader_context *ctx)
                                         radv_load_output(ctx, 
FRAG_RESULT_SAMPLE_MASK, 0));
        }
 
-       /* Export PS outputs. */
-       for (unsigned i = 0; i < index; i++)
-               ac_build_export(&ctx->ac, &color_args[i]);
-
        if (depth || stencil || samplemask)
-               radv_export_mrt_z(ctx, depth, stencil, samplemask);
-       else if (!index)
+               radv_export_mrt_z(ctx, depth, stencil, samplemask, &exp);
+       else if (last_color_export == -1 || last_non_null == -1)
                ac_build_export_null(&ctx->ac);
+
+       /* Export PS outputs. */
+       for (unsigned i = 0; i < exp.num; i++)
+               ac_build_export(&ctx->ac, &exp.args[i]);
 }
 
 static void
-- 
2.16.2

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