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Diffstat (limited to 'ghc/compiler/nativeGen/RegisterAlloc.hs')
| -rw-r--r-- | ghc/compiler/nativeGen/RegisterAlloc.hs | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/ghc/compiler/nativeGen/RegisterAlloc.hs b/ghc/compiler/nativeGen/RegisterAlloc.hs index 4f71fe1edb..7c5a4bdbb9 100644 --- a/ghc/compiler/nativeGen/RegisterAlloc.hs +++ b/ghc/compiler/nativeGen/RegisterAlloc.hs @@ -80,6 +80,58 @@ The algorithm is roughly: -} +{- +Possible plan for x86 floating pt register alloc: + + - The standard reg alloc procedure allocates pretend floating point + registers to the GXXX instructions. We need to convert these GXXX + instructions to proper x86 FXXX instructions, using the FP stack for + registers. + + We could do this in a separate pass, but it helps to have the + information about which real registers are live after the + instruction, so we do it at reg alloc time where that information + is already available. + + - keep a mapping from %fakeN to FP stack slot in the monad. + + - after assigning registers to the GXXX instruction, convert the + instruction to an FXXX instruction. eg. + - for GMOV just update the mapping, and ffree any dead regs. + - GLD: just fld and update mapping + GLDZ: just fldz and update mapping + GLD1: just fld1 and update mapping + - GST: just fst and update mapping, ffree dead regs. + - special case for GST reg, where reg is st(0), we can fstp. + - for GADD fp1, fp2, fp3: + - easy way: fld fp2 + fld fp1 + faddp + -- record that fp3 is now in %st(0), and all other + -- slots are pushed down one. + ffree fp1 -- if fp1 is dead now + ffree fp2 -- if fp2 is dead now + - optimisation #1 + - if fp1 is in %st(0) and is dead afterward + fadd %st(0), fp2 + -- record fp3 is in %st(0) + ffree fp2 -- if fp2 is dead now + - if fp2 is in %st(0) and is dead afterward + fadd %st(0), fp1 + -- record fp3 is in %st(0) + - if fp1 is in %st(0), fp2 is dead afterward + fadd fp2, %st(0) + -- record fp3 is in fp2's locn + - if fp2 is in %st(0), fp1 is dead afterward + fadd fp1, %st(0) + -- record fp3 is in fp1's locn + + - we should be able to avoid the nasty ffree problems of the current + scheme. The stack should be empty before doing a non-local + jump/call - we can assert that this is the case. +-} + + module RegisterAlloc ( regAlloc ) where |