radeonsi: fix a coherency issue when VS memory stores are not visible in PS

If a shader has no param exports (no varyings), the pixel shader can start
after the VS position is written before the vertex shader finishes.
The fix is to wait for the memory stores before the position export.

The code needs to be restructured. First prepare param exports to get
nr_param_exports, then emit position exports with the wait, and then
emit param exports.

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10813>

diff --git a/src/gallium/drivers/radeonsi/si_shader_llvm_vs.c b/src/gallium/drivers/radeonsi/si_shader_llvm_vs.c
index 602fce1..89adcfa 100644 (file)
--- a/src/gallium/drivers/radeonsi/si_shader_llvm_vs.c
+++ b/src/gallium/drivers/radeonsi/si_shader_llvm_vs.c
@@ -420,7 +420,7 @@ static void si_llvm_emit_clipvertex(struct si_shader_context *ctx, struct ac_exp
 }
 
 /* Initialize arguments for the shader export intrinsic */
-static void si_llvm_init_vs_export_args(struct si_shader_context *ctx, LLVMValueRef *values,
+static void si_llvm_init_vs_export_args(struct si_shader_context *ctx, const LLVMValueRef *values,
                                         unsigned target, struct ac_export_args *args)
 {
    args->enabled_channels = 0xf; /* writemask - default is 0xf */
@@ -432,16 +432,9 @@ static void si_llvm_init_vs_export_args(struct si_shader_context *ctx, LLVMValue
    memcpy(&args->out[0], values, sizeof(values[0]) * 4);
 }
 
-static void si_export_param(struct si_shader_context *ctx, unsigned index, LLVMValueRef *values)
-{
-   struct ac_export_args args;
-
-   si_llvm_init_vs_export_args(ctx, values, V_008DFC_SQ_EXP_PARAM + index, &args);
-   ac_build_export(&ctx->ac, &args);
-}
-
-static void si_build_param_exports(struct si_shader_context *ctx,
-                                   struct si_shader_output_values *outputs, unsigned noutput)
+static void si_prepare_param_exports(struct si_shader_context *ctx,
+                                     const struct si_shader_output_values *outputs, unsigned noutput,
+                                     struct ac_export_args exports[32])
 {
    struct si_shader *shader = ctx->shader;
    unsigned param_count = 0;
@@ -478,7 +471,8 @@ static void si_build_param_exports(struct si_shader_context *ctx,
              (1ull << si_shader_io_get_unique_index(semantic, true)))
          continue;
 
-      si_export_param(ctx, param_count, outputs[i].values);
+      si_llvm_init_vs_export_args(ctx, outputs[i].values, V_008DFC_SQ_EXP_PARAM + param_count,
+                                  &exports[param_count]);
 
       assert(i < ARRAY_SIZE(shader->info.vs_output_param_offset));
       shader->info.vs_output_param_offset[i] = param_count++;
@@ -570,6 +564,9 @@ void si_llvm_build_vs_exports(struct si_shader_context *ctx,
 
    si_vertex_color_clamping(ctx, outputs, noutput);
 
+   struct ac_export_args param_exports[32];
+   si_prepare_param_exports(ctx, outputs, noutput, param_exports);
+
    /* Build position exports. */
    for (i = 0; i < noutput; i++) {
       switch (outputs[i].semantic) {
@@ -719,15 +716,28 @@ void si_llvm_build_vs_exports(struct si_shader_context *ctx,
       /* Specify the target we are exporting */
       pos_args[i].target = V_008DFC_SQ_EXP_POS + pos_idx++;
 
-      if (pos_idx == shader->info.nr_pos_exports)
+      if (pos_idx == shader->info.nr_pos_exports) {
          /* Specify that this is the last export */
          pos_args[i].done = 1;
 
+         /* If a shader has no param exports, rasterization can start before
+          * the shader finishes and thus memory stores might not finish before
+          * the pixel shader starts.
+          *
+          * VLOAD is for atomics with return.
+          */
+         if (ctx->screen->info.chip_class >= GFX10 &&
+             !shader->info.nr_param_exports &&
+             shader->selector->info.base.writes_memory)
+            ac_build_waitcnt(&ctx->ac, AC_WAIT_VLOAD | AC_WAIT_VSTORE);
+      }
+
       ac_build_export(&ctx->ac, &pos_args[i]);
    }
 
    /* Build parameter exports. */
-   si_build_param_exports(ctx, outputs, noutput);
+   for (unsigned i = 0; i < shader->info.nr_param_exports; i++)
+      ac_build_export(&ctx->ac, &param_exports[i]);
 }
 
 void si_llvm_emit_vs_epilogue(struct ac_shader_abi *abi, unsigned max_outputs, LLVMValueRef *addrs)