implement the null function for the Mips32 subzero compiler

pydir/run-pnacl-sz.py

Index: pydir/run-pnacl-sz.py
diff --git a/pydir/run-pnacl-sz.py b/pydir/run-pnacl-sz.py
index 787910cc532a0efff3f291aaa776688bc2a780ef..72b6a0be9aab1e572caccd22fd3d932d4aae3a91 100755
--- a/pydir/run-pnacl-sz.py
+++ b/pydir/run-pnacl-sz.py
@@ -15,14 +15,18 @@ def TargetAssemblerFlags(target):
   # TODO(stichnot): -triple=i686-nacl should be used for a
   # sandboxing test.  This means there should be an args.sandbox
   # argument that also gets passed through to pnacl-sz.
+  # TODO(reed kotler). Need to find out exactly we need to
+  # add here for Mips32.
   flags = { 'x8632': ['-triple=i686'],
-            'arm32': ['-triple=armv7a', '-mcpu=cortex-a9', '-mattr=+neon'] }
+            'arm32': ['-triple=armv7a', '-mcpu=cortex-a9', '-mattr=+neon'],
+            'mips32': ['-triple=mipsel-none-nacl' ] }

[jvoung (off chromium), 2015/07/07 18:02:34]

Is it possible to leave out the "-none-nacl" for now, to be consistent with the
rest, or does that break the tests (if so, what does does the error look like)?

[reed.kotler, 2015/07/07 21:54:54]

for now it's needed but I will try and eliminate it in the future.

it will mess up the alignment in the assembler for nacl without it.

[jvoung (off chromium), 2015/07/08 00:39:11]

Hmm okay, can't think of why the alignment would be different from the arm case,
but could follow up on this later. You mean instruction bundling, etc.? I don't
think the tests would be checking for that, except for a few tests like
tests_lit/assembler/x86/sandboxing.ll, which we aren't running for ARM/MIPS. In
those cases it would be looking for nops.

[reed.kotler, 2015/07/08 02:05:16]

Yes, I think it had to do with instruction bundling. I did this before
vacation but if I remove it then a test fails now. I don't remember
the issues right now. I need to go through a lot of things still; 
not just this.

   return flags[target]
 
 
 def TargetDisassemblerFlags(target):
   flags = { 'x8632': ['-Mintel'],
-            'arm32': [] }
+            'arm32': [],
+            'mips32':[] }
   return flags[target]
 
 
@@ -73,7 +77,7 @@ def main():
                            choices=['obj', 'asm', 'iasm'],
                            help='Output file type.  Default %(default)s.')
     argparser.add_argument('--target', default='x8632', dest='target',
-                           choices=['x8632','arm32'],
+                           choices=['x8632','arm32','mips32'],
                            help='Target architecture.  Default %(default)s.')
     argparser.add_argument('--echo-cmd', required=False,
                            action='store_true',