Add the PUSH instruction to ARM integrated assembler.

tests_lit/assembler/arm32/push-pop.ll

+; Show that we know how to translate push and pop.
+; TODO(kschimpf) Translate pop instructions.
+
+; NOTE: We use -O2 to get rid of memory stores.
+
+; REQUIRES: allow_dump
+
+; Compile using standalone assembler.
+; RUN: %p2i --filetype=asm -i %s --target=arm32 --args -O2 -allow-extern \
+; RUN:   | FileCheck %s --check-prefix=ASM
+
+; Show bytes in assembled standalone code.
+; RUN: %p2i --filetype=asm -i %s --target=arm32 --assemble --disassemble \
+; RUN:   --args -O2 -allow-extern | FileCheck %s --check-prefix=DIS
+
+; Compile using integrated assembler.
+; RUN: %p2i --filetype=iasm -i %s --target=arm32 --args -O2 -unsafe-ias \
+; RUN:   -allow-extern | FileCheck %s --check-prefix=IASM
+
+; Show bytes in assembled integrated code.
+; RUN: %p2i --filetype=iasm -i %s --target=arm32 --assemble --disassemble \
+; RUN:   --args -O2 -unsafe-ias -allow-extern | FileCheck %s --check-prefix=DIS
+
+declare external void @DoSomething()
+
+define internal void @SinglePushPop() {
+  call void @DoSomething();
+  ret void       
+}
+
+; ASM-LABEL:SinglePushPop:
+; ASM-NEXT:.LSinglePushPop$__0:
+; ASM-NEXT:    push    {lr}
+; ASM:         sub     sp, sp, #12
+; ASM-NEXT:    bl      DoSomething
+; ASM:         add     sp, sp, #12
+; ASM-NEXT:    pop     {lr}
+; ASM:         bx      lr
+
+; DIS-LABEL:00000000 <SinglePushPop>:
+; DIS-NEXT:   0:        e52de004
+; DIS-NEXT:   4:        e24dd00c
+; DIS-NEXT:   8:        ebfffffe
+; DIS-NEXT:   c:        e28dd00c
+; DIS-NEXT:  10:        e49de004
+; DIS-NEXT:  14:        e12fff1e
+
+; IASM-LABEL:SinglePushPop:
+; IASM-NEXT:.LSinglePushPop$__0:
+; IASM-NEXT:    .byte 0x4
+; IASM-NEXT:    .byte 0xe0
+; IASM-NEXT:    .byte 0x2d
+; IASM-NEXT:    .byte 0xe5
+
+; IASM-NEXT:    .byte 0xc
+; IASM-NEXT:    .byte 0xd0
+; IASM-NEXT:    .byte 0x4d
+; IASM-NEXT:    .byte 0xe2
+; IASM-NEXT:    bl      DoSomething
+; IASM-NEXT:    .byte 0xc
+; IASM-NEXT:    .byte 0xd0
+; IASM-NEXT:    .byte 0x8d
+; IASM-NEXT:    .byte 0xe2
+; IASM-NEXT:    pop     {lr}
+
+; IASM:         .byte 0x1e
+; IASM-NEXT:    .byte 0xff
+; IASM-NEXT:    .byte 0x2f
+; IASM-NEXT:    .byte 0xe1
+
+define internal i32 @MultPushPop(i32 %v1, i32 %v2) {
+  call void @DoSomething();

[Jim Stichnoth, 2015/11/06 00:59:09]

Add a comment describing the trick: the over-eager O2 register allocator puts v1
and v2 into callee-save registers since the call instruction kills the scratch
registers, requiring these callee-save registers to be pushed/popped in the
prolog/epilog.

[Karl, 2015/11/06 17:14:30]

Done.

+  %v3 = add i32 %v1, %v2
+  ret i32 %v3
+}
+
+; ASM-LABEL:MultPushPop:
+; ASM-NEXT:.LMultPushPop$__0:
+; ASM-NEXT:     push    {r4, r5, lr}
+; ASM:          sub     sp, sp, #4
+; ASM-NEXT:     mov     r4, r0
+; ASM-NEXT:     mov     r5, r1
+; ASM-NEXT:     bl      DoSomething
+; ASM:          add     r4, r4, r5
+; ASM-NEXT:     mov     r0, r4
+; ASM-NEXT:     add     sp, sp, #4
+; ASM-NEXT:     pop     {r4, r5, lr}
+; ASM:          bx      lr
+
+; DIS-LABEL:00000020 <MultPushPop>:
+; DIS-NEXT:  20:        e92d4030
+; DIS-NEXT:  24:        e24dd004
+; DIS-NEXT:  28:        e1a04000
+; DIS-NEXT:  2c:        e1a05001
+; DIS-NEXT:  30:        ebfffffe
+; DIS-NEXT:  34:        e0844005
+; DIS-NEXT:  38:        e1a00004
+; DIS-NEXT:  3c:        e28dd004
+; DIS-NEXT:  40:        e8bd4030
+; DIS-NEXT:  44:        e12fff1e
+
+; IASM-LABEL:MultPushPop:
+; IASM-NEXT:.LMultPushPop$__0:
+; IASM-NEXT:    .byte 0x30
+; IASM-NEXT:    .byte 0x40
+; IASM-NEXT:    .byte 0x2d
+; IASM-NEXT:    .byte 0xe9
+
+; IASM-NEXT:    .byte 0x4
+; IASM-NEXT:    .byte 0xd0
+; IASM-NEXT:    .byte 0x4d
+; IASM-NEXT:    .byte 0xe2
+
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0x40
+; IASM-NEXT:    .byte 0xa0
+; IASM-NEXT:    .byte 0xe1
+
+; IASM-NEXT:    .byte 0x1
+; IASM-NEXT:    .byte 0x50
+; IASM-NEXT:    .byte 0xa0
+; IASM-NEXT:    .byte 0xe1
+
+; IASM-NEXT:    bl      DoSomething
+; IASM-NEXT:    .byte 0x5
+; IASM-NEXT:    .byte 0x40
+; IASM-NEXT:    .byte 0x84
+; IASM-NEXT:    .byte 0xe0
+
+; IASM-NEXT:    .byte 0x4
+; IASM-NEXT:    .byte 0x0
+; IASM-NEXT:    .byte 0xa0
+; IASM-NEXT:    .byte 0xe1
+
+; IASM-NEXT:    .byte 0x4
+; IASM-NEXT:    .byte 0xd0
+; IASM-NEXT:    .byte 0x8d
+; IASM-NEXT:    .byte 0xe2
+; IASM-NEXT:    pop     {r4, r5, lr}
+
+; IASM:         .byte 0x1e
+; IASM-NEXT:    .byte 0xff
+; IASM-NEXT:    .byte 0x2f
+; IASM-NEXT:    .byte 0xe1