malc c878da3b27 tcg/ppc32: Use trampolines to trim the code size for mmu slow path accessors ... mmu access looks something like: <check tlb> if miss goto slow_path <fast path> done: ... ; end of the TB slow_path: <pre process> mr r3, r27 ; move areg0 to r3 ; (r3 holds the first argument for all the PPC32 ABIs) <call mmu_helper> b $+8 .long done <post process> b done On ppc32 <call mmu_helper> is: (SysV and Darwin) mmu_helper is most likely not within direct branching distance from the call site, necessitating a. moving 32 bit offset of mmu_helper into a GPR ; 8 bytes b. moving GPR to CTR/LR ; 4 bytes c. (finally) branching to CTR/LR ; 4 bytes r3 setting - 4 bytes call - 16 bytes dummy jump over retaddr - 4 bytes embedded retaddr - 4 bytes Total overhead - 28 bytes (PowerOpen (AIX)) a. moving 32 bit offset of mmu_helper's TOC into a GPR1 ; 8 bytes b. loading 32 bit function pointer into GPR2 ; 4 bytes c. moving GPR2 to CTR/LR ; 4 bytes d. loading 32 bit small area pointer into R2 ; 4 bytes e. (finally) branching to CTR/LR ; 4 bytes r3 setting - 4 bytes call - 24 bytes dummy jump over retaddr - 4 bytes embedded retaddr - 4 bytes Total overhead - 36 bytes Following is done to trim the code size of slow path sections: In tcg_target_qemu_prologue trampolines are emitted that look like this: trampoline: mfspr r3, LR addi r3, 4 mtspr LR, r3 ; fixup LR to point over embedded retaddr mr r3, r27 <jump mmu_helper> ; tail call of sorts And slow path becomes: slow_path: <pre process> <call trampoline> .long done <post process> b done call - 4 bytes (trampoline is within code gen buffer and most likely accessible via direct branch) embedded retaddr - 4 bytes Total overhead - 8 bytes In the end the icache pressure is decreased by 20/28 bytes at the cost of an extra jump to trampoline and adjusting LR (to skip over embedded retaddr) once inside. Signed-off-by: malc <av1474@comtv.ru>		2012-11-06 04:37:57 +04:00
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tcg-target.c	tcg/ppc32: Use trampolines to trim the code size for mmu slow path accessors	2012-11-06 04:37:57 +04:00
tcg-target.h	tcg: Remove TCG_TARGET_HAS_GUEST_BASE define	2012-10-12 14:27:05 +03:00