[SubZero] Generate spin-lock for atomic load store

src/IceTargetLowering.def

 //===- subzero/src/IceTargetLowering.def - Target X-macros ------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines certain platform independent patterns for lowering target
@@ skipping 27 matching lines @@
   X(fptoui_f64_i32,     "__Sz_fptoui_f64_i32")                                 \
   X(fptoui_f64_i64,     "__Sz_fptoui_f64_i64")                                 \
   X(frem_f32,           "fmodf")                                               \
   X(frem_f64,           "fmod")                                                \
   X(sdiv_i32,           "__divsi3")                                            \
   X(sdiv_i64,           "__divdi3")                                            \
   X(sitofp_i64_f32,     "__Sz_sitofp_i64_f32")                                 \
   X(sitofp_i64_f64,     "__Sz_sitofp_i64_f64")                                 \
   X(srem_i32,           "__modsi3")                                            \
   X(srem_i64,           "__moddi3")                                            \
+  X(sync_f_n_add_8,     "__sync_fetch_and_add_8")                              \

[Jim Stichnoth, 2017/02/10 07:16:19]

Unfortunately I just discovered a problem with this way of adding MIPS-specific
helper functions.

When I run "make presubmit", the sandboxed cross tests fail because these
symbols are undefined.

The problem is that with -filetype=obj, explicit references to all these symbols
are added to the ELF object file.  Even though they are not actually used, the
pnacl-ld linker gives an error when no definitions are provided.

The solution is to look up these symbols only as needed, instead of adding them
to the unconditionally-instantiated RuntimeHelperFunc[] table at startup.

Look at the uses of __aeabi_read_tp as an example of how this is done for that
ARM-specific symbol.

Also, please document these functions at the bottom of runtime/szrt.c.  Maybe
just put them under a new section e.g.:

// MIPS runtime library:
//   __sync_fetch_and_add_8
//   __sync_fetch_and_and_8
//   ...

[jaydeep.patil, 2017/02/10 08:31:24]

Done.

+  X(sync_f_n_and_8,     "__sync_fetch_and_and_8")                              \
+  X(sync_f_n_or_8,      "__sync_fetch_and_or_8")                               \
+  X(sync_f_n_sub_8,     "__sync_fetch_and_sub_8")                              \
+  X(sync_f_n_xor_8,     "__sync_fetch_and_xor_8")                              \
+  X(sync_lock_tset_8,   "__sync_lock_test_and_set_8")                          \
+  X(sync_val_cx_8,      "__sync_val_compare_and_swap_8")                       \
   X(udiv_i32,           "__udivsi3")                                           \
   X(udiv_i64,           "__udivdi3")                                           \
   X(uitofp_4xi32_4xf32, "__Sz_uitofp_4xi32_4xf32")                             \
   X(uitofp_i32_f32,     "__Sz_uitofp_i32_f32")                                 \
   X(uitofp_i32_f64,     "__Sz_uitofp_i32_f64")                                 \
   X(uitofp_i64_f32,     "__Sz_uitofp_i64_f32")                                 \
   X(uitofp_i64_f64,     "__Sz_uitofp_i64_f64")                                 \
   X(urem_i32,           "__umodsi3")                                           \
   X(urem_i64,           "__umoddi3")
 //#define X(Tag, Name)
 
 #endif // SUBZERO_SRC_ICETARGETLOWERING_DEF