Add DMB instruction to the ARM integrated assembler.

tests_lit/assembler/arm32/dmb.ll

+; Show that we know how to encode the dmb instruction.
+
+; REQUIRES: allow_dump
+
+; Compile using standalone assembler.
+; RUN: %p2i --filetype=asm -i %s --target=arm32 --args -Om1 \
+; RUN:   | FileCheck %s --check-prefix=ASM
+
+; Show bytes in assembled standalone code.
+; RUN: %p2i --filetype=asm -i %s --target=arm32 --assemble --disassemble \
+; RUN:   --args -Om1 | FileCheck %s --check-prefix=DIS
+
+; Compile using integrated assembler.
+; RUN: %p2i --filetype=iasm -i %s --target=arm32 --args -Om1 \
+; RUN:   | FileCheck %s --check-prefix=IASM
+
+; Show bytes in assembled integrated code.
+; RUN: %p2i --filetype=iasm -i %s --target=arm32 --assemble --disassemble \
+; RUN:   --args -Om1 | FileCheck %s --check-prefix=DIS
+
+declare i8 @llvm.nacl.atomic.load.i8(i8*, i32)
+
+define internal i32 @test_atomic_load_8(i32 %iptr) {
+; ASM-LABEL:test_atomic_load_8:
+; DIS-LABEL:00000000 <test_atomic_load_8>:
+; IASM-LABEL:test_atomic_load_8:
+
+entry:
+; ASM-NEXT:.Ltest_atomic_load_8$entry:
+; IASM-NEXT:.Ltest_atomic_load_8$entry:
+
+; ASM-NEXT:     sub     sp, sp, #12
+; DIS-NEXT:   0:        e24dd00c
+; IASM-NEXT:    .byte 0xc
+; IASM-NEXT:    .byte 0xd0
+; IASM-NEXT:    .byte 0x4d
+; IASM-NEXT:    .byte 0xe2
+
+; ASM-NEXT:     str     r0, [sp, #8]
+; ASM-NEXT:     # [sp, #8] = def.pseudo 
+; DIS-NEXT:   4:        e58d0008
+; IASM-NEXT:    .byte 0x8
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0x8d
+; IASM-NEXT:    .byte 0xe5
+
+  %ptr = inttoptr i32 %iptr to i8*
+  ; parameter value "6" is for the sequential consistency memory order.
+  %i = call i8 @llvm.nacl.atomic.load.i8(i8* %ptr, i32 6)
+
+; ASM-NEXT:     ldr     r0, [sp, #8]
+; DIS-NEXT:   8:        e59d0008
+; IASM-NEXT:    .byte 0x8
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0x9d
+; IASM-NEXT:    .byte 0xe5
+
+; ASM-NEXT:     ldrb    r0, [r0]
+; DIS-NEXT:   c:        e5d00000
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0xd0
+; IASM-NEXT:    .byte 0xe5
+
+; ASM-NEXT:     dmb     sy
+; DIS-NEXT:  10:        f57ff05f
+; IASM-NEXT:    .byte 0x5f
+; IASM-NEXT:    .byte 0xf0
+; IASM-NEXT:    .byte 0x7f
+; IASM-NEXT:    .byte 0xf5
+
+  %r = zext i8 %i to i32
+  ret i32 %r
+}