Edinburgh IMP77 Compiler - Version 8.4 1 ! .Ltext0: .globl main main: .LFB189: 2 ! The hand-generated code below should be producable by PSR's compiler if it: 3 ! A) delays stores as late as possible 4 ! 5 ! B) remembers registers over procedure calls 6 ! 7 ! C) has a general algorithm for drop-through conditionally executed 8 ! instructions, i.e. if there are no instructions between a conditional 9 ! branch and its destination which set the condition codes, and the 10 ! sequence is less that a certain length, then all the instructions 11 ! within the sequence can be made conditional. 12 ! 13 ! D) does as above, but also allows instructions within the sequence 14 ! whose subsequent execution depends on the same condition, e.g. 15 ! 16 ! %if a=b %and c=d %then a=b 17 ! 18 ! CmpS R0,R1 NAIVE STYLE 19 ! Bne elsepart 20 ! Cmps R2,R3 21 ! Bne elsepart 22 ! Mov R0,R2 23 ! 24 ! CmpS R0,R1 RULE (C) ABOVE 25 ! Bne elsepart 26 ! CmpS R2,R3 27 ! MovEQ R0,R2 28 ! 29 ! CmpS R0,R1 RULE (D) SPECIAL CASE 30 ! CmpSEQ R2,R3 31 ! MovEQ R0,R2 32 ! 33 ! E) alters conditions to generate similar condition codes on 34 ! condition AND condition AND condition to generate more cases 35 ! to which rule (D) can be applied. 36 ! 37 ! F) adjusts constants in < or <= cases to favour above, i.e. turning 38 ! CMP R,#const & BLE ... into CMP R,#const-1 & BLT ... etc. 39 ! 40 ! G) changes Newline back from the current implicit printsymbol(10) - 41 ! there is no run-time overhead in moving the MOV R0,#10 over to 42 ! the procedure body instead of having it in every call where it 43 ! takes up space - after all, Peter's code-moving stuff ought to 44 ! get %permroutine newline;printsymbol(10);%end correct - it will 45 ! place the Mov R0,#10 before the body of %permroutine printsymbol 46 ! and generate a suitable entry point for it... 47 ! Personally, I would recommend stacking/restoring R0 as well 48 ! as it might keep another variable in a register for a bit longer... 49 ! 50 ! I've only suggested optimisations which fit into the style of PSR's 51 ! compilers... 52 ! 53 54 55 %begin leal 4(%esp), %ecx andl $-16, %esp pushl -4(%ecx) pushl %ebp movl %esp, %ebp pushl %ebx pushl %ecx subl $320, %esp call __x86.get_pc_thunk.bx addl $_GLOBAL_OFFSET_TABLE_, %ebx movl %ecx, %eax movl 4(%eax), %edx movl %edx, -316(%ebp) movl %gs:20, %ecx movl %ecx, -12(%ebp) xorl %ecx, %ecx subl $8, %esp pushl -316(%ebp) pushl (%eax) call _imp_initialise@PLT addl $16, %esp 56 %integer a,i,b 57 58 read(a) subl $12, %esp leal -300(%ebp), %eax pushl %eax call _imp_readint@PLT addl $16, %esp 59 ! BL read_fn 60 61 ! Str R0,a 62 read(i) subl $12, %esp leal -296(%ebp), %eax pushl %eax call _imp_readint@PLT addl $16, %esp 63 ! BL read_fn 64 65 ! Str R0,i 66 read(b) subl $12, %esp leal -292(%ebp), %eax pushl %eax call _imp_readint@PLT addl $16, %esp .LBB17: 67 ! BL read_fn 68 69 %if a <= i <= b %start movl -296(%ebp), %eax movl %eax, -284(%ebp) movl -300(%ebp), %eax cmpl %eax, -284(%ebp) jl .L16 movl -292(%ebp), %eax cmpl %eax, -284(%ebp) jg .L17 .LBE17: nop jmp .L3 .L17: nop .L3: .LBE18: .LBB19: 70 ! Ldr R1,a 71 ! Ldr R2,i 72 ! CmpS R1,R2 73 ! CmpSLE R2,R0 74 i = 22 movl $22, -296(%ebp) jmp .L3 .L16: .LBB18: 75 ! MovLE R2,#22 76 %finish 77 78 %if 22 <= i <= b %start movl -296(%ebp), %eax movl %eax, -288(%ebp) cmpl $21, -288(%ebp) jle .L18 movl -292(%ebp), %eax cmpl %eax, -288(%ebp) jg .L19 .LBE19: nop jmp .L6 .L19: nop .L6: .LBE20: .LBB21: 79 ! CmpS R2,#22-1 80 ! CmpSGT R2,R0 81 i = 44 movl $44, -296(%ebp) jmp .L6 .L18: .LBB20: 82 ! MovGT R2,#44 83 %finish 84 85 %if a <= i <= 77 %start movl -296(%ebp), %eax movl %eax, -280(%ebp) movl -300(%ebp), %eax cmpl %eax, -280(%ebp) jl .L20 cmpl $77, -280(%ebp) jg .L21 .LBE21: nop jmp .L9 .L21: nop .L9: .LBE22: .LBB23: 86 ! CmpS R1,R2 87 ! CmpSLE R2,#77 88 i = 99 movl $99, -296(%ebp) jmp .L9 .L20: .LBB22: 89 ! MovLE R2,#99 90 %finish 91 92 %if 11 <= i <= 100 %start ;! Peter's special case when both const is good movl -296(%ebp), %eax movl %eax, -276(%ebp) cmpl $10, -276(%ebp) jle .L22 cmpl $100, -276(%ebp) jg .L23 .LBE23: nop jmp .L15 .L23: nop .L15: .LBE24: 93 ! Sub R2,#11 ;! but usually corrupts a register needed later 94 ! CmpS R2,#100-11 95 i = 1 movl $1, -296(%ebp) jmp .L15 .L12: .L22: .LBB24: 96 ! MovLS R2,#1 97 %finish 98 99 ! Str R0,b 100 write(a,0) movl -300(%ebp), %eax subl $8, %esp pushl $0 pushl %eax call _imp_writeint@PLT addl $16, %esp .LBB25: .LBB26: call _imp_newline@PLT .LBE26: .LBE25: 101 ! Mov R0,R1 102 ! Mov R1,#0 103 ! Bl Write 104 105 newline 106 ! Bl Newline 107 108 ! Mov R0,R2 109 write(i,0) movl -296(%ebp), %eax subl $8, %esp pushl $0 pushl %eax call _imp_writeint@PLT addl $16, %esp .LBB27: .LBB28: call _imp_newline@PLT .LBE28: .LBE27: 110 ! Bl write 111 112 newline 113 ! Bl newline 114 115 write(b,0) movl -292(%ebp), %eax subl $8, %esp pushl $0 pushl %eax call _imp_writeint@PLT addl $16, %esp .LBB29: .LBB30: call _imp_newline@PLT movl $0, -272(%ebp) .LBE30: .LBE29: .LBB31: .LBB32: subl $12, %esp pushl -272(%ebp) call exit@PLT .LBE32: .LBE31: .LFE189: .section .text.__x86.get_pc_thunk.bx,"axG",@progbits,__x86.get_pc_thunk.bx,comdat .globl __x86.get_pc_thunk.bx .hidden __x86.get_pc_thunk.bx __x86.get_pc_thunk.bx: .LFB190: movl (%esp), %ebx ret .LFE190: .Letext0: 116 ! Ldr R0,b 117 ! Bl write 118 119 newline 120 ! Bl newline 121 122 %endofprogram 24 Statements compiled