[PATCH] ARM: Emit ".code 16" before global inline-asm instructions in thumb mode

[Akira Hatanaka]

ToT clang (correctly) errors-out when the target is armv7 (thumb2) and the
program it's compiling has an ARM mode file-level inline assembly
statement:

$ cat test2.c

__asm__ ("stmib sp, {r0-r14};");


$ clang -arch armv7  -S -o - test2.c

.section __TEXT,__text,regular,pure_instructions

.ios_version_min 5, 0

.section __TEXT,__textcoal_nt,coalesced,pure_instructions

.section __TEXT,__const_coal,coalesced

.section __TEXT,__picsymbolstub4,symbol_stubs,none,16

.section __TEXT,__StaticInit,regular,pure_instructions

.section __TEXT,__cstring,cstring_literals

.syntax unified

                                        @ Start of file scope inline
assembly

*<inline asm>:1:1: **error: **instruction requires: arm-mode*

stmib sp, {r0-r14};

However, when the .s file is generated with -no-integrated-as first, and
then assembled later, clang completes assembling the .s file without any
errors.

$ clang -arch armv7  -S -o test2.s -no-integrated-as test2.c

$ clang -arch armv7  test2.s -c


The attached patch fixes this discrepancy in clang's behavior by emitting
directive ".code 16" before global inline-asm instructions when the target
is thumb. Without this directive, clang assembles the global inline-asm
instruction in ARM mode, since the assembler always starts in ARM mode and
stays in that mode until it sees directives that instruct it to switch to
thumb.

<rdar://problem/17757232>
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