Noticed today that the GCC C compiler generated an unexpected sequence of instructions for an AND and TEST:
**** bool overflow = (ccpm & carrybit) != 0; // check if carry bit set 109 .loc 1 189 0 110 0078 5810B25C l %r1,604(%r11) # D.7949, ccpm 111 007c 5410B26C n %r1,620(%r11) # D.7949, carrybit 112 0080 1011 lpr %r1,%r1 # tmp54, D.7949 113 0082 1311 lcr %r1,%r1 # tmp55, tmp54 114 0084 8810001F srl %r1,31 # tmp56, 115 0088 4210B25B stc %r1,603(%r11) # tmp56, overflow I can only guess this is to avoid the cost of a branch? Or is there some other advantage in this? Best wishes / Mejores deseos / Meilleurs vœux Ian ...
