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 --command %p2i --filetype=asm --assemble \

[jvoung (off chromium), 2015/07/07 18:02:35]

Can you add the "--need=allow_dump " that is now part of the ARM variant? I had
left that out previously.

[reed.kotler, 2015/07/08 02:05:17]

Done.

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

[jvoung (off chromium), 2015/07/07 18:02:35]

this line also requires a "--need=allow_dump" before the --command FileCheck

[reed.kotler, 2015/07/08 02:05:17]

Done.

 
 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
+; TODO (Reed Kotler check this disassembly, .s file looks fine)

[jvoung (off chromium), 2015/07/07 18:02:35]

"TODO(reed kotler)" for consistency

Or just leave out the TODO if it looks fine?

[reed.kotler, 2015/07/08 02:05:17]

Done.

+; MIPS32-LABEL: foo
+; MIPS32: 4: {{.*}} jr ra
+; MIPS32-NEXT: 8: {{.*}} nop
+; MIPS32-NEXT: c: e7fedef0

[jvoung (off chromium), 2015/07/07 18:02:35]

I think the main TODO is that "e7fedef0" is an "undefined"/halting instruction
for ARM (what llvm.trap would translate to).

[reed.kotler, 2015/07/07 21:54:55]

Done.

 
 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)

[jvoung (off chromium), 2015/07/07 18:02:35]

Probably don't need a TODO, since this block doesn't have the iffy "e7fedef0"
check.

[reed.kotler, 2015/07/07 21:54:55]

Done.

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

Doesn't appear to be removed?

[reed.kotler, 2015/07/08 02:05:17]

Done.

+; MIPS32-LABEL: bar
+; MIPS32: 14: {{.*}} jr ra
+; MIPS32-NEXT: 18: {{.*}} nop