Experiment to speed up libco and hence libsnes (#2248)
The compiler now can fully inline the co_switch, and with most registers being specified as clobbers and not saved explicitly, the compiler can choose to save only what it needs to (we don't have to defensively save everything). Practically speaking, the co_switch calls are usually inlined, but the functions they're in don't seem to be that big and don't make direct use of r12..r15 too much anyway, so (push r12..r15, switch, pop r12..r15) is a common emit. But I see a miniscule FPS increase.
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nattthebear
GitHub
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commit
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@ -1,8 +1,8 @@
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NO_WBX_TARGETS := 1
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CCFLAGS := -std=c99 -Wall
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SRCS := amd64.c coswap.s
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AS := nasm
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ASFLAGS := -f elf64 -Wall
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SRCS := amd64.c #coswap.s
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#AS := nasm
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#ASFLAGS := -f elf64 -Wall
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include ../common.mak
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@ -10,7 +10,7 @@ $(OBJ_DIR)/%.s.o: %.s
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@echo as $<
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@mkdir -p $(@D)
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@$(AS) $(ASFLAGS) -o $@ $<
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$(DOBJ_DIR)/%.s.o: %.s
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@echo as $<
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@mkdir -p $(@D)
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@$(AS) $(ASFLAGS) -o $@ $<
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# $(DOBJ_DIR)/%.s.o: %.s
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# @echo as $<
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# @mkdir -p $(@D)
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# @$(AS) $(ASFLAGS) -o $@ $<
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@ -20,12 +20,8 @@ typedef struct {
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// used by coswap.s, has to be at the beginning of the struct
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struct {
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uint64_t rsp;
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uint64_t rbp;
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uint64_t rbx;
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uint64_t r12;
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uint64_t r13;
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uint64_t r14;
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uint64_t r15;
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uint64_t rbp; // we have to save rbp because unless fomit-frame-pointer is set, the compiler regards it as "special" and won't allow clobbers
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uint64_t rip;
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} jmp_buf;
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// points to the lowest address in the stack
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// NB: because of guard space, this is not valid stack
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@ -104,8 +100,8 @@ cothread_t co_create(unsigned int sz, void (*entrypoint)(void))
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{
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uint64_t* p = (uint64_t*)((char*)co->stack + co->stack_size); // seek to top of stack
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*--p = (uint64_t)crash; // crash if entrypoint returns
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*--p = (uint64_t)entrypoint; // start of function
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co->jmp_buf.rsp = (uint64_t)p; // stack pointer
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co->jmp_buf.rip = (uint64_t)entrypoint; // start of function
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}
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return co;
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@ -116,40 +112,41 @@ void co_delete(cothread_t handle)
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free_thread(handle);
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}
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// static uint64_t hoststart;
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// static uint64_t hostend;
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void co_switch(cothread_t handle)
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{
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cothread_impl* co = handle;
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cothread_impl* co_previous_handle = co_active_handle;
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co_active_handle = co;
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// uint64_t start;
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// uint64_t end;
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// if (co_active_handle == &co_host_buffer)
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// {
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// // migrating off of real thread; save stack params
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// __asm__("movq %%gs:0x08, %0": "=r"(end));
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// __asm__("movq %%gs:0x10, %0": "=r"(start));
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// hoststart = start;
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// hostend = end;
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// }
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// if (handle == &co_host_buffer)
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// {
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// // migrating onto real thread; load stack params
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// start = hoststart;
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// end = hostend;
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// hoststart = 0;
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// hostend = 0;
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// }
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// else
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// {
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// // migrating onto cothread; compute its extents we allocated them
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// start = (uintptr_t)co->stack;
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// end = start + co->stack_size;
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// }
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// __asm__("movq %0, %%gs:0x08":: "r"(end));
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// __asm__("movq %0, %%gs:0x10":: "r"(start));
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register uint64_t _rdi __asm__("rdi") = (uint64_t)co_previous_handle;
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register uint64_t _rsi __asm__("rsi") = (uint64_t)co_active_handle;
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register cothread_impl* co_previous_handle = co_active_handle;
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co_swap(co_active_handle = co, co_previous_handle);
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/*
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mov [rdi + 0], rsp
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mov [rdi + 8], rbp
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lea rax, [rip + 17]
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mov [rdi + 16], rax
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mov rsp, [rsi + 0]
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mov rbp, [rsi + 8]
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mov rax, [rsi + 16]
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jmp rax
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*/
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__asm__(
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"mov %%rsp, 0(%%rdi)\n"
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"mov %%rbp, 8(%%rdi)\n"
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"lea 17(%%rip), %%rax\n"
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"mov %%rax, 16(%%rdi)\n"
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"mov 0(%%rsi), %%rsp\n"
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"mov 8(%%rsi), %%rbp\n"
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"mov 16(%%rsi), %%rax\n"
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"jmp *%%rax\n"
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::"r"(_rdi), "r"(_rsi)
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:"rax", "rbx", "rcx", "rdx", /*"rbp",*/ /*"rsi", "rdi",*/ "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15",
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"zmm0", "zmm1", "zmm2", "zmm3", "zmm4", "zmm5", "zmm6", "zmm7", "zmm8", "zmm9",
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"zmm10", "zmm11", "zmm12", "zmm13", "zmm14", "zmm15",
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/*"zmm16", "zmm17", "zmm18", "zmm19",
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"zmm20", "zmm21", "zmm22", "zmm23", "zmm24", "zmm25", "zmm26", "zmm27", "zmm28", "zmm29",
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"zmm30", "zmm31",*/
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"memory"
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);
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}
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@ -1,21 +0,0 @@
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section .text
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global co_swap
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align 16
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co_swap:
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mov [rsi],rsp
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mov rsp,[rdi]
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pop rax
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mov [rsi+ 8],rbp
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mov [rsi+16],rbx
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mov [rsi+24],r12
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mov [rsi+32],r13
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mov [rsi+40],r14
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mov [rsi+48],r15
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mov rbp,[rdi+ 8]
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mov rbx,[rdi+16]
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mov r12,[rdi+24]
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mov r13,[rdi+32]
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mov r14,[rdi+40]
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mov r15,[rdi+48]
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jmp rax
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