i965: Free dead GLSL IR one last time.

While working on NIR's memory allocation model, I realized the GLSL IR
memory model was broken.

During glCompileShader, we allocate everything out of the
_mesa_glsl_parse_state context, and reparent it to gl_shader at the end.

During glLinkProgram, we allocate everything out of a temporary context,
then reparent it to the exec_list containing the linked IR.

But during brw_link_shader - the driver's final opportunity to do
lowering and optimization - we just allocated everything out of the
permanent context given to us by the linker.  That memory stayed
forever.

Notably, passes like brw_fs_channel_expressions cause us to churn the
majority of the code, so we really want to free dead IR here.

Saves 125MB of memory when replaying a Dota 2 trace on Broadwell.

Signed-off-by: Kenneth Graunke <[email protected]>
Reviewed-by: Jason Ekstrand <[email protected]>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp b/src/mesa/drivers/dri/i965/brw_shader.cpp
index 4ef38829beb..54d6d71cc7a 100644
--- a/src/mesa/drivers/dri/i965/brw_shader.cpp
+++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
@@ -144,6 +144,11 @@ brw_link_shader(struct gl_context *ctx, struct gl_shader_program *shProg)
 
       _mesa_copy_linked_program_data((gl_shader_stage) stage, shProg, prog);
 
+      /* Temporary memory context for any new IR. */
+      void *mem_ctx = ralloc_context(NULL);
+
+      ralloc_adopt(mem_ctx, shader->base.ir);
+
       bool progress;
 
       /* lower_packing_builtins() inserts arithmetic instructions, so it
@@ -250,6 +255,13 @@ brw_link_shader(struct gl_context *ctx, struct gl_shader_program *shProg)
 
       _mesa_reference_program(ctx, &prog, NULL);
 
+      /* Now that we've finished altering the linked IR, reparent any live IR back
+       * to the permanent memory context, and free the temporary one (discarding any
+       * junk we optimized away).
+       */
+      reparent_ir(shader->base.ir, shader->base.ir);
+      ralloc_free(mem_ctx);
+
       if (ctx->_Shader->Flags & GLSL_DUMP) {
          fprintf(stderr, "\n");
          fprintf(stderr, "GLSL IR for linked %s program %d:\n",