I've been working on a gcc patch targeting 64-bit Wine to reduce the impact of the implicit register clobbers when a Microsoft's x64 function calls a System V ABI function and I appear to finally have a working implementation. However, I cannot get recent Wine tests to complete with an unpatched compiler (I have 30 failures, 4 which are crashes and I even get some dmesgs from drivers.) While the same Wine tests pass both with and without the new optimization, I could use some external testing to make sure there's no flaws that I've missed (especially a full test with no failures).
The patch set is not actually complete as my unit tests didn't catch many of the flaws (now fixed) that I caught when building real Wine, so I'm re-working them. I have my current version up on github: https://github.com/daniel-santos/gcc/tree/gcc-5_4_0-outline-msabi-xlogues.
Background For those unfamiliar, the differences between the two ABIs requires an ms_abi function to save and restore 12 registers: RSI, RDI and XMM6-15. The size of pushing/popping RSI and RDI is insignificant, but saving and restoring 10 SSE registers takes between 94 and 174 bytes each function (dependent upon the SP offset), thereby bloating ".text" size quite a bit.
Details This patch uses out-of-line stubs for register for saves/restores to reduce .text size. The *theory* (not yet proven) is that the reduction of instruction cache misses will offset the extra few instructions required to facilitate this. But while we're going this far, the optimization also saves/restores an additional 6 non-volatile ms_abi registers if they are clobbered in the function: RBX, RBP and R12-15. This extra step actually saves very little ".text" code, but the stub implements them using MOVs which the CPU is better able to parallelize. While MOV instructions are larger (4 bytes vs 1 or 2), they only appear in the stubs, theoretically gaining the performance benefits of MOVs without paying for the cost of the extra size.
This optimization works both with and without forced stack realignment (https://bugs.winehq.org/show_bug.cgi?id=27680), although more can be done to produce better code in the realigned case. In the forced realignment case, this optimization reduces .text size Wine 64 by 19% and in the normal (aligned stack) case by 22%. As an example, here is a test function (with stubs) built with -foutline-msabi-xlogues (but no realignment):
__attribute__ ((noinline)) long sysv_fn0 () { return 42; }
__attribute__ ((ms_abi, noinline)) long msabifn0_6 () { __asm__ __volatile__ ("" ::: "rbx", "rbp", "r12", "r13", "r14", "r15"); return sysv_fn0 (); }
0000000000401000 <msabifn0_6>: 401000: 48 8d 44 24 88 lea -0x78(%rsp),%rax 401005: 48 81 ec f8 00 00 00 sub $0xf8,%rsp 40100c: e8 09 e8 01 00 callq 41f81a <__msabi_save_18> 401011: 31 c0 xor %eax,%eax 401013: e8 48 fc ff ff callq 400c60 <sysv_fn0> 401018: 48 8d b4 24 80 00 00 lea 0x80(%rsp),%rsi 40101f: 00 401020: 4c 8d 56 78 lea 0x78(%rsi),%r10 401024: e9 41 e8 01 00 jmpq 41f86a <__msabi_restore_ret_18>
000000000041f81a <__msabi_save_18>: 41f81a: 4c 89 78 90 mov %r15,-0x70(%rax) 000000000041f81e <__msabi_save_17>: 41f81e: 4c 89 70 98 mov %r14,-0x68(%rax) 000000000041f822 <__msabi_save_16>: 41f822: 4c 89 68 a0 mov %r13,-0x60(%rax) 000000000041f826 <__msabi_save_15>: 41f826: 4c 89 60 a8 mov %r12,-0x58(%rax) 000000000041f82a <__msabi_save_14>: 41f82a: 48 89 68 b0 mov %rbp,-0x50(%rax) 000000000041f82e <__msabi_save_13>: 41f82e: 48 89 58 b8 mov %rbx,-0x48(%rax) 000000000041f832 <__msabi_save_12>: 41f832: 48 89 78 c0 mov %rdi,-0x40(%rax) 41f836: 48 89 70 c8 mov %rsi,-0x38(%rax) 41f83a: 44 0f 29 78 d0 movaps %xmm15,-0x30(%rax) 41f83f: 44 0f 29 70 e0 movaps %xmm14,-0x20(%rax) 41f844: 44 0f 29 68 f0 movaps %xmm13,-0x10(%rax) 41f849: 44 0f 29 20 movaps %xmm12,(%rax) 41f84d: 44 0f 29 58 10 movaps %xmm11,0x10(%rax) 41f852: 44 0f 29 50 20 movaps %xmm10,0x20(%rax) 41f857: 44 0f 29 48 30 movaps %xmm9,0x30(%rax) 41f85c: 44 0f 29 40 40 movaps %xmm8,0x40(%rax) 41f861: 0f 29 78 50 movaps %xmm7,0x50(%rax) 41f865: 0f 29 70 60 movaps %xmm6,0x60(%rax) 41f869: c3 retq
000000000041f86a <__msabi_restore_ret_18>: 41f86a: 4c 8b 7e 90 mov -0x70(%rsi),%r15 000000000041f86e <__msabi_restore_ret_17>: 41f86e: 4c 8b 76 98 mov -0x68(%rsi),%r14 000000000041f872 <__msabi_restore_ret_16>: 41f872: 4c 8b 6e a0 mov -0x60(%rsi),%r13 000000000041f876 <__msabi_restore_ret_15>: 41f876: 4c 8b 66 a8 mov -0x58(%rsi),%r12 000000000041f87a <__msabi_restore_ret_14>: 41f87a: 48 8b 6e b0 mov -0x50(%rsi),%rbp 000000000041f87e <__msabi_restore_ret_13>: 41f87e: 48 8b 5e b8 mov -0x48(%rsi),%rbx 000000000041f882 <__msabi_restore_ret_12>: 41f882: 48 8b 7e c0 mov -0x40(%rsi),%rdi 41f886: 44 0f 28 7e d0 movaps -0x30(%rsi),%xmm15 41f88b: 44 0f 28 76 e0 movaps -0x20(%rsi),%xmm14 41f890: 44 0f 28 6e f0 movaps -0x10(%rsi),%xmm13 41f895: 44 0f 28 26 movaps (%rsi),%xmm12 41f899: 44 0f 28 5e 10 movaps 0x10(%rsi),%xmm11 41f89e: 44 0f 28 56 20 movaps 0x20(%rsi),%xmm10 41f8a3: 44 0f 28 4e 30 movaps 0x30(%rsi),%xmm9 41f8a8: 44 0f 28 46 40 movaps 0x40(%rsi),%xmm8 41f8ad: 0f 28 7e 50 movaps 0x50(%rsi),%xmm7 41f8b1: 0f 28 76 60 movaps 0x60(%rsi),%xmm6 41f8b5: 48 8b 76 c8 mov -0x38(%rsi),%rsi 41f8b9: 4c 89 d4 mov %r10,%rsp 41f8bc: c3 retq
Here is a similar function with forced realignment. This can be improved with an additional "have frame pointer" set of stubs.
__attribute__ ((ms_abi, noinline, force_align_arg_pointer)) long msabifn0_5 () { __asm__ __volatile__ ( "" ::: "rbx", "r12", "r13", "r14", "r15" ); return sysv_fn0 (); }
0000000000400fc0 <msabifn0_5>: 400fc0: 55 push %rbp 400fc1: 48 8d 44 24 90 lea -0x70(%rsp),%rax 400fc6: 48 89 e5 mov %rsp,%rbp 400fc9: 48 83 e0 f0 and $0xfffffffffffffff0,%rax 400fcd: 48 8d 60 b0 lea -0x50(%rax),%rsp 400fd1: e8 78 e8 01 00 callq 41f84e <__msabi_save_13> 400fd6: 41 57 push %r15 400fd8: 41 56 push %r14 400fda: 41 55 push %r13 400fdc: 41 54 push %r12 400fde: 31 c0 xor %eax,%eax 400fe0: e8 7b fc ff ff callq 400c60 <sysv_fn0> 400fe5: 48 8d a5 20 ff ff ff lea -0xe0(%rbp),%rsp 400fec: 41 5c pop %r12 400fee: 41 5d pop %r13 400ff0: 41 5e pop %r14 400ff2: 41 5f pop %r15 400ff4: 48 8d 74 24 50 lea 0x50(%rsp),%rsi 400ff9: e8 a0 e8 01 00 callq 41f89e <__msabi_restore_13> 400ffe: 48 81 c4 c0 00 00 00 add $0xc0,%rsp 401005: 5d pop %rbp 401006: c3 retq
Daniel