tree 5fda881ed412b71013e1f2445ed5ddd1a7b37470
parent 2048b01dfec8877d672a4da41a158f68b12b5337
author Aart Bik <ajcbik@google.com> 1456963573 -0800
committer Aart Bik <ajcbik@google.com> 1457630569 -0800

Avoid generating dead code on frame enter/exit.
This includes stack operations and, on x86, call/pop to read PC.

bug=26997690

Rationale:
(1) If method is fully intrinsified, and makes no calls in slow
    path or uses special input, no need to require current method.
(2) Invoke instructions with HasPcRelativeDexCache() generate code
    that reads the PC (call/pop) on x86. However, if the invoke is
    an intrinsic that is later replaced with actual code, this PC
    reading code may be dead.

Example X86 (before/after):

0x0000108c: 83EC0C      sub esp, 12
0x0000108f: 890424      mov [esp], eax       <-- not needed
0x00001092: E800000000  call +0 (0x00001097)
0x00001097: 58          pop eax              <-- dead code to read PC
0x00001098: F30FB8C1    popcnt eax, ecx
0x0000109c: F30FB8DA    popcnt ebx, edx
0x000010a0: 03D8        add ebx, eax
0x000010a2: 89D8        mov eax, ebx
0x000010a4: 83C40C      add esp, 12          <-- not needed
0x000010a7: C3          ret

0x0000103c: F30FB8C1    popcnt eax, ecx
0x00001040: F30FB8DA    popcnt ebx, edx
0x00001044: 03D8        add ebx, eax
0x00001046: 89D8        mov eax, ebx
0x00001048: C3          ret

Example ARM64 (before/after):

0x0000103c: f81e0fe0      str x0, [sp, #-32]!
0x00001040: f9000ffe      str lr, [sp, #24]
0x00001044: dac01020      clz x0, x1
0x00001048: f9400ffe      ldr lr, [sp, #24]
0x0000104c: 910083ff      add sp, sp, #0x20 (32)
0x00001050: d65f03c0      ret

0x0000103c: dac01020      clz x0, x1
0x00001040: d65f03c0      ret

Change-Id: I8377db80c9a901a08fff4624927cf4a6e585da0c