4.1.4. 根据目标平台调整选项
从c_common_post_options返回，继续process_options。回忆input_filename访问input_location的file域，这个域记录了当前正在编译的文件。
process_options (continue)
4283 input_filename = main_input_filename;
4284
4285 #ifdef OVERRIDE_OPTIONS
4286 /* Some machines may reject certain combinations of options. */
4287 OVERRIDE_OPTIONS;
4288 #endif
如果后端对于与目标平台相关的编译选项有特定的要求，则定义上面4285行的宏OVERRIDER_OPTIONS，提供自己的处理句柄。对于x86目标平台，这个宏被定义为以下的函数。
1050 void
1051 override_options (void) in i386.c
1052 {
1053 int i;
1054 /* Comes from final.c -- no real reason to change it. */
1055 #define MAX_CODE_ALIGN 16
1056
1057 static struct ptt
1058 {
1059 const struct processor_costs *cost; /* Processor costs */
1060 const int target_enable; /* Target flags to enable. */
1061 const int target_disable; /* Target flags to disable. */
1062 const int align_loop; /* Default alignments. */
1063 const int align_loop_max_skip;
1064 const int align_jump;
1065 const int align_jump_max_skip;
1066 const int align_func;
1067 }
1068 const processor_target_table[PROCESSOR_max] =
1069 {
1070 {&i386_cost, 0, 0, 4, 3, 4, 3, 4},
1071 {&i486_cost, 0, 0, 16, 15, 16, 15, 16},
1072 {&pentium_cost, 0, 0, 16, 7, 16, 7, 16},
1073 {&pentiumpro_cost, 0, 0, 16, 15, 16, 7, 16},
1074 {&k6_cost, 0, 0, 32, 7, 32, 7, 32},
1075 {&athlon_cost, 0, 0, 16, 7, 16, 7, 16},
1076 {&pentium4_cost, 0, 0, 0, 0, 0, 0, 0},
1077 {&k8_cost, 0, 0, 16, 7, 16, 7, 16}
1078 };
1079
1080 static const char * const cpu_names[] = TARGET_CPU_DEFAULT_NAMES;
1081 static struct pta
1082 {
1083 const char *const name; /* processor name or nickname. */
1084 const enum processor_type processor;
1085 const enum pta_flags
1086 {
1087 PTA_SSE = 1,
1088 PTA_SSE2 = 2,
1089 PTA_SSE3 = 4,
1090 PTA_MMX = 8,
1091 PTA_PREFETCH_SSE = 16,
1092 PTA_3DNOW = 32,
1093 PTA_3DNOW_A = 64,
1094 PTA_64BIT = 128
1095 } flags;
1096 }
1097 const processor_alias_table[] =
1098 {
1099 {"i386", PROCESSOR_I386, 0},
1100 {"i486", PROCESSOR_I486, 0},
1101 {"i586", PROCESSOR_PENTIUM, 0},
1102 {"pentium", PROCESSOR_PENTIUM, 0},
1103 {"pentium-mmx", PROCESSOR_PENTIUM, PTA_MMX},
1104 {"winchip-c6", PROCESSOR_I486, PTA_MMX},
1105 {"winchip2", PROCESSOR_I486, PTA_MMX | PTA_3DNOW},
1106 {"c3", PROCESSOR_I486, PTA_MMX | PTA_3DNOW},
1107 {"c3-2", PROCESSOR_PENTIUMPRO, PTA_MMX | PTA_PREFETCH_SSE | PTA_SSE},
1108 {"i686", PROCESSOR_PENTIUMPRO, 0},
1109 {"pentiumpro", PROCESSOR_PENTIUMPRO, 0},
1110 {"pentium2", PROCESSOR_PENTIUMPRO, PTA_MMX},
1111 {"pentium3", PROCESSOR_PENTIUMPRO, PTA_MMX | PTA_SSE | PTA_PREFETCH_SSE},
1112 {"pentium3m", PROCESSOR_PENTIUMPRO, PTA_MMX | PTA_SSE | PTA_PREFETCH_SSE},
1113 {"pentium-m", PROCESSOR_PENTIUMPRO, PTA_MMX | PTA_SSE | PTA_PREFETCH_SSE | PTA_SSE2},
1114 {"pentium4", PROCESSOR_PENTIUM4, PTA_SSE | PTA_SSE2
1115 | PTA_MMX | PTA_PREFETCH_SSE},
1116 {"pentium4m", PROCESSOR_PENTIUM4, PTA_SSE | PTA_SSE2
1117 | PTA_MMX | PTA_PREFETCH_SSE},
1118 {"prescott", PROCESSOR_PENTIUM4, PTA_SSE | PTA_SSE2 | PTA_SSE3
1119 | PTA_MMX | PTA_PREFETCH_SSE},
1120 {"nocona", PROCESSOR_PENTIUM4, PTA_SSE | PTA_SSE2 | PTA_SSE3 | PTA_64BIT
1121 | PTA_MMX | PTA_PREFETCH_SSE},
1122 {"k6", PROCESSOR_K6, PTA_MMX},
1123 {"k6-2", PROCESSOR_K6, PTA_MMX | PTA_3DNOW},
1124 {"k6-3", PROCESSOR_K6, PTA_MMX | PTA_3DNOW},
1125 {"athlon", PROCESSOR_ATHLON, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW
1126 | PTA_3DNOW_A},
1127 {"athlon-tbird", PROCESSOR_ATHLON, PTA_MMX | PTA_PREFETCH_SSE
1128 | PTA_3DNOW | PTA_3DNOW_A},
1129 {"athlon-4", PROCESSOR_ATHLON, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW
1130 | PTA_3DNOW_A | PTA_SSE},
1131 {"athlon-xp", PROCESSOR_ATHLON, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW
1132 | PTA_3DNOW_A | PTA_SSE},
1133 {"athlon-mp", PROCESSOR_ATHLON, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW
1134 | PTA_3DNOW_A | PTA_SSE},
1135 {"x86-64", PROCESSOR_K8, PTA_MMX | PTA_PREFETCH_SSE | PTA_64BIT
1136 | PTA_SSE | PTA_SSE2 },
1137 {"k8", PROCESSOR_K8, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW | PTA_64BIT
1138 | PTA_3DNOW_A | PTA_SSE | PTA_SSE2},
1139 {"opteron", PROCESSOR_K8, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW | PTA_64BIT
1140 | PTA_3DNOW_A | PTA_SSE | PTA_SSE2},
1141 {"athlon64", PROCESSOR_K8, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW | PTA_64BIT
1142 | PTA_3DNOW_A | PTA_SSE | PTA_SSE2},
1143 {"athlon-fx", PROCESSOR_K8, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW | PTA_64BIT
1144 | PTA_3DNOW_A | PTA_SSE | PTA_SSE2},
1145 };
1146
1147 int const pta_size = ARRAY_SIZE (processor_alias_table);
上面，processor_target_table和processor_alias_table的类型定义在它们之前，因此这些类型不能用于别处。在1080行的TARGET_CPU_DEFAULT_NAMES定义了CPU族。
710 #define TARGET_CPU_DEFAULT_NAMES {"i386", "i486", "pentium", "pentium-mmx",/
711 "pentiumpro", "pentium2", "pentium3", /
712 "pentium4", "k6", "k6-2", "k6-3",/
713 "athlon", "athlon-4", "k8", /
714 "pentium-m", "prescott", "nocona"}
在1085行的pta_flags描述了特定芯片上可用的寄存器集的属性。
override_options (continue)
1149 /* Set the default values for switches whose default depends on TARGET_64BIT
1150 in case they weren't overwritten by command line options. */
1151 if (TARGET_64BIT)
1152 {
1153 if (flag_omit_frame_pointer == 2)
1154 flag_omit_frame_pointer = 1;
1155 if (flag_asynchronous_unwind_tables == 2)
1156 flag_asynchronous_unwind_tables = 1;
1157 if (flag_pcc_struct_return == 2)
1158 flag_pcc_struct_return = 0;
1159 }
1160 else
1161 {
1162 if (flag_omit_frame_pointer == 2)
1163 flag_omit_frame_pointer = 0;
1164