1 files changed, 20 insertions, 0 deletions
diff --git a/src/mesa/drivers/dri/i965/brw_context.h b/src/mesa/drivers/dri/i965/brw_context.h
index be59e3b0d16..550eefedcc2 100644
--- a/src/mesa/drivers/dri/i965/brw_context.h
+++ b/src/mesa/drivers/dri/i965/brw_context.h
@@ -1713,6 +1713,26 @@ bool brw_lower_texture_gradients(struct brw_context *brw,
 extern const char * const conditional_modifier[16];
 extern const char *const pred_ctrl_align16[16];
 
+static inline bool
+brw_depth_writes_enabled(const struct brw_context *brw)
+{
+   const struct gl_context *ctx = &brw->ctx;
+
+   /* We consider depth writes disabled if the depth function is GL_EQUAL,
+    * because it would just overwrite the existing depth value with itself.
+    *
+    * These bonus depth writes not only use bandwidth, but they also can
+    * prevent early depth processing.  For example, if the pixel shader
+    * discards, the hardware must invoke the to determine whether or not
+    * to do the depth write.  If writes are disabled, we may still be able
+    * to do the depth test before the shader, and skip the shader execution.
+    *
+    * The Broadwell 3DSTATE_WM_DEPTH_STENCIL documentation also contains
+    * a programming note saying to disable depth writes for EQUAL.
+    */
+   return ctx->Depth.Test && ctx->Depth.Mask && ctx->Depth.Func != GL_EQUAL;
+}
+
 void
 brw_emit_depthbuffer(struct brw_context *brw);