implement the null function for the Mips32 subzero compiler

tests_lit/llvm2ice_tests/function_aligned.ll

 ; Test that functions are aligned to the NaCl bundle alignment.
 ; We could be smarter and only do this for indirect call targets
 ; but typically you want to align functions anyway.
 ; Also, we are currently using hlts for non-executable padding.
 
 ; RUN: %p2i --filetype=obj --disassemble -i %s --args -O2 | FileCheck %s
 
 ; TODO(jvoung): Stop skipping unimplemented parts (via --skip-unimplemented)
 ; once enough infrastructure is in. Also, switch to --filetype=obj
 ; when possible.
 ; RUN: %if --need=target_ARM32 --need=allow_dump \
 ; RUN:   --command %p2i --filetype=asm --assemble \
 ; RUN:   --disassemble --target arm32 -i %s --args -O2 --skip-unimplemented \
 ; RUN:   | %if --need=target_ARM32 --need=allow_dump \
 ; RUN:   --command FileCheck --check-prefix ARM32 %s
+; RUN: %if --need=target_MIPS32 --need=allow_dump --command %p2i --filetype=asm --assemble \

[jvoung (off chromium), 2015/07/08 00:39:12]

Since there is "\" at the end of the line to wrap and avoid spilling over 80
cols, you could wrap earlier. Otherwise this is now spilling over 80 cols.

E.g., could wrap earlier like the ARM versions.

+; RUN:   --disassemble --target mips32 -i %s --args -O2 --skip-unimplemented \
+; RUN:   | %if --need=target_MIPS32 --need=allow_dump --command FileCheck --check-prefix MIPS32 %s

[jvoung (off chromium), 2015/07/08 00:39:12]

similar, could wrap earlier

 
 define void @foo() {
   ret void
 }
 ; CHECK-LABEL: foo
 ; CHECK-NEXT: 0: {{.*}} ret
 ; CHECK-NEXT: 1: {{.*}} hlt
 ; ARM32-LABEL: foo
 ; ARM32-NEXT: 0: {{.*}} bx lr
 ; ARM32-NEXT: 4: e7fedef0 udf
 ; ARM32-NEXT: 8: e7fedef0 udf
 ; ARM32-NEXT: c: e7fedef0 udf
+; MIPS32-LABEL: foo
+; MIPS32: 4: {{.*}} jr ra
+; MIPS32-NEXT: 8: {{.*}} nop
+; MIPS32-NEXT: c: e7fedef0
+; TODO (reed kotler check this disassembly, .s file looks fine)

[jvoung (off chromium), 2015/07/08 00:39:12]

"TODO (reed kotler" -> "TODO(reed kotler)"

+; "e7fedef0" is an "undefined"/halting instruction for ARM (what llvm.trap would translate to)
 
 define void @bar() {
   ret void
 }
 ; CHECK-LABEL: bar
 ; CHECK-NEXT: 20: {{.*}} ret
 ; ARM32-LABEL: bar
 ; ARM32-NEXT: 10: {{.*}} bx lr
+; TOOD (Reed Kotler check this disassembly, .s file looks fine)
+; MIPS32-LABEL: bar
+; MIPS32: 14: {{.*}} jr ra
+; MIPS32-NEXT: 18: {{.*}} nop