• Aurelien Jarno's avatar
    tcg: initial ia64 support · 477ba620
    Aurelien Jarno authored
    A few words about design choices:
    * On IA64, instructions should be grouped by bundle, and dependencies
      between instructions declared. A first version of this code tried to
      schedule instructions automatically, but was very complex and too
      invasive for the current common TCG code (ops not ending at
      instruction boundaries, code retranslation breaking already generated
      code, etc.)  It was also not very efficient, as dependencies between
      TCG ops is not available.
      Instead the option taken by the current implementation does not try
      to fill the bundle by scheduling instructions, but by providing ops
      not available as an ia64 instruction, and by offering 22-bit constant
      loading for most of the instructions. With both options the bundle are
      filled at approximately the same level.
    
    * Up to 128 registers can be affected to a function on IA64, but TCG
      limits this number to 64, which is actually more than enough. The
      register affectation is the following:
      - r0: used to map a constant argument with value 0
      - r1: global pointer
      - r2, r3: internal use
      - r4 to r6: not used to avoid saving them
      - r7: env structure
      - r8 to r11: free for TCG (call clobbered)
      - r12: stack pointer
      - r13: thread pointer
      - r14 to r31: free for TCG (call clobbered)
      - r32: reserved (return address)
      - r33: reserved (PFS)
      - r33 to r63: free for TCG
    
    * The IA64 architecture has only 64-bit registers and no 32-bit
      instructions (the only exception being cmp4). Therefore 64-bit
      registers and instructions are used for 32-bit ops. The adopted
      strategy is the same as the ABI, that is the higher 32 bits are
      undefined. Most ops (and, or, add, shl, etc.) can directly use
      the 64-bit registers, while some others have to sign-extend (sar,
      div, etc.) or zero-extend (shr, divu, etc.) the register first.
    Signed-off-by: default avatarAurelien Jarno <aurelien@aurel32.net>
    477ba620
cpu-common.h 4.85 KB