Implement tail-call optimization.
This commit is contained in:
Chris Pressey
parent
78a1f2910c
commit
92b1cfeefb
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@ -14,9 +14,11 @@ History of SixtyPical
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* Added `--prune-unreachable-routines` option, which causes
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the compiler to in fact omit routines determined to be
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unreachable as described above.
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* Code generation now performs modest peephole optimization,
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generating better code for `goto`s and `if` blocks at the
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end of a routine.
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* Code generation now performs modest peephole optimization
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at the end of each routine. This results in better code
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generation for constructs in tail position, notably
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tail optimization of `calls`, but also for `goto`s and
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`if` blocks at the end of a routine.
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* The `dcc6502-adapter` test adapter was updated to conform
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to the output of the latest version of `dcc6502`.
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7
TODO.md
7
TODO.md
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@ -83,13 +83,6 @@ This is not just an impressive trick -- in the presence of local pointers, which
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use up a word in zero-page, which we consider a precious resource, it allow those
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zero-page locations to be re-used.
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### Tail-call optimization
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If a block ends in a `call` can that be converted to end in a `goto`? Why not? I think it can,
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if the block is in tail position. The constraints should iron out the same both ways.
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As long as the routine has consistent type context every place it exits, that should be fine.
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Implementation
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--------------
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@ -167,6 +167,15 @@ class Compiler(object):
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needs_rts = True
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last_op = self.emitter.get_tail()
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if isinstance(last_op, JSR):
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if isinstance(last_op.operand, Absolute):
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if isinstance(last_op.operand.value, Label):
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label = last_op.operand.value
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self.emitter.retract()
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self.emitter.emit(JMP(Absolute(label)))
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last_op = self.emitter.get_tail()
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if isinstance(last_op, JMP):
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needs_rts = False
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if isinstance(last_op.operand, Absolute):
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@ -51,10 +51,12 @@ Call extern.
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| {
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| ld a, 65
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| call chrout
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| ld a, 0
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| }
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= $080D LDA #$41
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= $080F JSR $FFD2
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= $0812 RTS
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= $0812 LDA #$00
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= $0814 RTS
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Call defined routine.
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@ -71,13 +73,39 @@ Call defined routine.
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| trashes a, x, y, z, n
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| {
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| call foo
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| ld a, 1
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| }
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= $080D JSR $0811
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= $0810 RTS
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= $0811 LDA #$00
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= $0813 LDX #$00
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= $0815 LDY #$00
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= $0817 RTS
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= $080D JSR $0813
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= $0810 LDA #$01
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= $0812 RTS
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= $0813 LDA #$00
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= $0815 LDX #$00
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= $0817 LDY #$00
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= $0819 RTS
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Tail call is optimized into a jump.
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| define foo routine
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| outputs a, x, y
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| trashes z, n
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| {
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| ld a, 0
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| ld x, 0
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| ld y, 0
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| }
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| define main routine
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| trashes a, x, y, z, n
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| {
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| ld a, 1
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| call foo
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| }
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= $080D LDA #$01
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= $080F JMP $0812
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= $0812 LDA #$00
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= $0814 LDX #$00
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= $0816 LDY #$00
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= $0818 RTS
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Access a defined memory location.
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@ -1053,7 +1081,7 @@ Copy word to word table and back, with constant offsets.
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= $0848 STA $084D
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= $084B RTS
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Indirect call.
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Indirect call. TODO: we don't need the final RTS here, omit it.
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| vector routine
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| outputs x
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@ -1074,16 +1102,15 @@ Indirect call.
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| copy bar, foo
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| call foo
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| }
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= $080D LDA #$1B
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= $080F STA $0822
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= $080D LDA #$1A
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= $080F STA $0821
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= $0812 LDA #$08
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= $0814 STA $0823
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= $0817 JSR $081E
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= $081A RTS
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= $081B LDX #$C8
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= $081D RTS
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= $081E JMP ($0822)
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= $0821 RTS
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= $0814 STA $0822
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= $0817 JMP $081D
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= $081A LDX #$C8
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= $081C RTS
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= $081D JMP ($0821)
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= $0820 RTS
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Compiling `goto`. Note that no `RTS` is emitted after the `JMP`.
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@ -1137,28 +1164,27 @@ Copying to and from a vector table.
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| call one
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| }
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= $080D LDX #$00
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= $080F LDA #$3F
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= $0811 STA $0846
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= $080F LDA #$3E
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= $0811 STA $0845
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= $0814 LDA #$08
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= $0816 STA $0847
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= $0819 LDA #$3F
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= $081B STA $0848,X
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= $0816 STA $0846
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= $0819 LDA #$3E
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= $081B STA $0847,X
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= $081E LDA #$08
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= $0820 STA $0948,X
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= $0823 LDA $0846
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= $0826 STA $0848,X
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= $0829 LDA $0847
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= $082C STA $0948,X
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= $082F LDA $0848,X
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= $0832 STA $0846
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= $0835 LDA $0948,X
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= $0838 STA $0847
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= $083B JSR $0842
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= $083E RTS
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= $083F LDX #$C8
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= $0841 RTS
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= $0842 JMP ($0846)
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= $0845 RTS
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= $0820 STA $0947,X
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= $0823 LDA $0845
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= $0826 STA $0847,X
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= $0829 LDA $0846
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= $082C STA $0947,X
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= $082F LDA $0847,X
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= $0832 STA $0845
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= $0835 LDA $0947,X
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= $0838 STA $0846
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= $083B JMP $0841
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= $083E LDX #$C8
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= $0840 RTS
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= $0841 JMP ($0845)
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= $0844 RTS
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Copying to and from a vector table, with constant offsets.
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@ -1188,28 +1214,27 @@ Copying to and from a vector table, with constant offsets.
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| call one
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| }
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= $080D LDX #$00
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= $080F LDA #$3F
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= $0811 STA $0846
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= $080F LDA #$3E
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= $0811 STA $0845
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= $0814 LDA #$08
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= $0816 STA $0847
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= $0819 LDA #$3F
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= $081B STA $0849,X
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= $0816 STA $0846
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= $0819 LDA #$3E
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= $081B STA $0848,X
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= $081E LDA #$08
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= $0820 STA $0949,X
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= $0823 LDA $0846
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= $0826 STA $084A,X
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= $0829 LDA $0847
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= $082C STA $094A,X
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= $082F LDA $084B,X
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= $0832 STA $0846
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= $0835 LDA $094B,X
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= $0838 STA $0847
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= $083B JSR $0842
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= $083E RTS
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= $083F LDX #$C8
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= $0841 RTS
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= $0842 JMP ($0846)
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= $0845 RTS
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= $0820 STA $0948,X
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= $0823 LDA $0845
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= $0826 STA $0849,X
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= $0829 LDA $0846
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= $082C STA $0949,X
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= $082F LDA $084A,X
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= $0832 STA $0845
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= $0835 LDA $094A,X
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= $0838 STA $0846
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= $083B JMP $0841
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= $083E LDX #$C8
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= $0840 RTS
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= $0841 JMP ($0845)
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= $0844 RTS
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### add, sub
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@ -1695,15 +1720,14 @@ just the same as initialized global storage locations are.
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| ld x, t
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| call foo
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| }
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= $080D LDX $081F
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= $0810 JSR $0814
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= $0813 RTS
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= $0814 STX $081E
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= $0817 INC $081E
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= $081A LDX $081E
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= $081D RTS
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= $081E .byte $FF
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= $081F .byte $07
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= $080D LDX $081E
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= $0810 JMP $0813
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= $0813 STX $081D
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= $0816 INC $081D
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= $0819 LDX $081D
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= $081C RTS
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= $081D .byte $FF
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= $081E .byte $07
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Memory locations defined local dynamic to a routine are allocated
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just the same as uninitialized global storage locations are.
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@ -1728,13 +1752,12 @@ just the same as uninitialized global storage locations are.
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| call foo
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| }
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= $080D LDX #$00
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= $080F STX $0821
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= $0812 JSR $0816
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= $0815 RTS
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= $0816 STX $0820
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= $0819 INC $0820
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= $081C LDX $0820
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= $081F RTS
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= $080F STX $0820
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= $0812 JMP $0815
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= $0815 STX $081F
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= $0818 INC $081F
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= $081B LDX $081F
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= $081E RTS
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Memory locations defined local dynamic to a routine are allocated
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just the same as uninitialized global storage locations are, even
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@ -1761,9 +1784,8 @@ when declared with a fixed address.
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| }
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= $080D LDX #$00
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= $080F STX $0401
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= $0812 JSR $0816
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= $0815 RTS
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= $0816 STX $0400
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= $0819 INC $0400
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= $081C LDX $0400
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= $081F RTS
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= $0812 JMP $0815
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= $0815 STX $0400
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= $0818 INC $0400
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= $081B LDX $0400
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= $081E RTS
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