gallium/tgsi: Add support for barriers.

src/gallium/docs/source/tgsi.rst

@@ -1514,6 +1514,55 @@ Resource Access Opcodes
                ignored.
 
 
+.. _threadsyncopcodes:
+
+Inter-thread synchronization opcodes
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+These opcodes are intended for communication between threads running
+within the same compute grid.  For now they're only valid in compute
+programs.
+
+.. opcode:: MFENCE - Memory fence
+
+  Syntax: ``MFENCE resource``
+
+  Example: ``MFENCE RES[0]``
+
+  This opcode forces strong ordering between any memory access
+  operations that affect the specified resource.  This means that
+  previous loads and stores (and only those) will be performed and
+  visible to other threads before the program execution continues.
+
+
+.. opcode:: LFENCE - Load memory fence
+
+  Syntax: ``LFENCE resource``
+
+  Example: ``LFENCE RES[0]``
+
+  Similar to MFENCE, but it only affects the ordering of memory loads.
+
+
+.. opcode:: SFENCE - Store memory fence
+
+  Syntax: ``SFENCE resource``
+
+  Example: ``SFENCE RES[0]``
+
+  Similar to MFENCE, but it only affects the ordering of memory stores.
+
+
+.. opcode:: BARRIER - Thread group barrier
+
+  ``BARRIER``
+
+  This opcode suspends the execution of the current thread until all
+  the remaining threads in the working group reach the same point of
+  the program.  Results are unspecified if any of the remaining
+  threads terminates or never reaches an executed BARRIER instruction.
+
+
 Explanation of symbols used
 ------------------------------