string< on simple-base-strings producing suspicious code

[Paul F. Dietz]

(defun f1 (s1 s2) (declare (optimize speed (safety 0) (debug 0) (compilation-speed 0) (space 2)) (type simple-base-string s1 s2)) (string<= s1 s2))

It produces both a call to %SP-STRING-COMPARE, and some complicated branching.

(disassemble 'f1) ==>

; disassembly for F1
; Size: 167 bytes. Origin: #x52D4C06D ; F1
; 06D: 4C894DE8 MOV [RBP-24], R9
; 071: 4C8945E0 MOV [RBP-32], R8
; 075: 4D8B50F9 MOV R10, [R8-7]
; 079: 4C8955F8 MOV [RBP-8], R10
; 07D: 4D8B61F9 MOV R12, [R9-7]
; 081: 4C8965F0 MOV [RBP-16], R12
; 085: 488D4424F0 LEA RAX, [RSP-16]
; 08A: 4883EC30 SUB RSP, 48
; 08E: 498BD0 MOV RDX, R8
; 091: 31FF XOR EDI, EDI
; 093: 498BF2 MOV RSI, R10
; 096: 4C8948F0 MOV [RAX-16], R9
; 09A: 488978E8 MOV [RAX-24], RDI
; 09E: 4C8960E0 MOV [RAX-32], R12
; 0A2: B90C000000 MOV ECX, 12
; 0A7: 488928 MOV [RAX], RBP
; 0AA: 488BE8 MOV RBP, RAX
; 0AD: B802BD4450 MOV EAX, #x5044BD02 ; #<FDEFN SB-KERNEL:%SP-STRING-COMPARE>
; 0B2: FFD0 CALL RAX
; 0B4: 4C8B45E0 MOV R8, [RBP-32]
; 0B8: 4C8B4DE8 MOV R9, [RBP-24]
; 0BC: 4C8B65F0 MOV R12, [RBP-16]
; 0C0: 4C8B55F8 MOV R10, [RBP-8]
; 0C4: 488BDA MOV RBX, RDX
; 0C7: 4881FB17001050 CMP RBX, #x50100017 ; NIL
; 0CE: 7509 JNE L1
; 0D0: 498BD2 MOV RDX, R10
; 0D3: L0: 488BE5 MOV RSP, RBP
; 0D6: F8 CLC
; 0D7: 5D POP RBP
; 0D8: C3 RET
; 0D9: L1: 488BD3 MOV RDX, RBX
; 0DC: 4939D2 CMP R10, RDX
; 0DF: 7505 JNE L3
; 0E1: L2: 488BD3 MOV RDX, RBX
; 0E4: EBED JMP L0
; 0E6: L3: 488BD3 MOV RDX, RBX
; 0E9: 4939D4 CMP R12, RDX
; 0EC: 7507 JNE L5
; 0EE: L4: BA17001050 MOV EDX, #x50100017 ; NIL
; 0F3: EBDE JMP L0
; 0F5: L5: 488BD3 MOV RDX, RBX
; 0F8: 48D1FA SAR RDX, 1
; 0FB: 410FB6441001 MOVZX EAX, BYTE PTR [R8+RDX+1]
; 101: 488BD3 MOV RDX, RBX
; 104: 48D1FA SAR RDX, 1
; 107: 410FB64C1101 MOVZX ECX, BYTE PTR [R9+RDX+1]
; 10D: 4839C8 CMP RAX, RCX
; 110: 72CF JB L2
; 112: EBDA JMP L4

[Stas Boukarev (stassats)]

SB-KERNEL:%SP-STRING-COMPARE returns the first non-matching index, then it has to decide whether it's >, or <, or >=, etc.

[Stas Boukarev (stassats)]

7441f3b09404f18492caa6a73e1963dec80f1d50