［转载］LCC编译器的源程序分析(54)指令模式匹配

在 LCC 编译器里，先把下面的语句翻译成中间表示，

int nTest1 = 1;

其中间表示的树如下：

ASGNI4(ADDRLP4(nTest1), CNSTI4(1))

然后根据上述的中间表示进行指令模式匹配。

下面的函数 _label 就是进行这样的工作：

#001 static void _label(NODEPTR_TYPE a) {

#002  int c;

#003  struct _state *p;

#004 

#005  if (!a)

#006         fatal("_label", "Null tree/n", 0);

#007  STATE_LABEL(a) = p = allocate(sizeof *p, FUNC);

#008  p->rule._stmt = 0;

#009  ...

#010  switch (OP_LABEL(a)) {

#011  case 41: /* ARGB */

#012  

#013  ...

#014  case 4149: /* ASGNI4 */

#015         _label(LEFT_CHILD(a));

#016         _label(RIGHT_CHILD(a));

#017         if ( /* stmt: ASGNI4(VREGP,reg) */

#018               LEFT_CHILD(a)->op == 711 /* VREGP */

#019         ) {

#020                c = ((struct _state *)(RIGHT_CHILD(a)->x.state))->cost[_reg_NT] + 0;

#021               if (c + 0 < p->cost[_stmt_NT]) {

#022                    p->cost[_stmt_NT] = c + 0;

#023                    p->rule._stmt = 6;

#024               }

#025         }

#026         if ( /* stmt: ASGNI4(addr,ADDI4(mem,con1)) */

#027               RIGHT_CHILD(a)->op == 4405 /* ADDI4 */

#028         ) {

#029                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#030 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_con1_NT] + (memop(a));

#031               if (c + 0 < p->cost[_stmt_NT]) {

#032                    p->cost[_stmt_NT] = c + 0;

#033                    p->rule._stmt = 14;

#034               }

#035         }

#036         if ( /* stmt: ASGNI4(addr,ADDU4(mem,con1)) */

#037               RIGHT_CHILD(a)->op == 4406 /* ADDU4 */

#038         ) {

#039                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#040 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_con1_NT] + (memop(a));

#041               if (c + 0 < p->cost[_stmt_NT]) {

#042                    p->cost[_stmt_NT] = c + 0;

#043                    p->rule._stmt = 15;

#044               }

#045         }

#046         if ( /* stmt: ASGNI4(addr,SUBI4(mem,con1)) */

#047               RIGHT_CHILD(a)->op == 4421 /* SUBI4 */

#048         ) {

#049                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#050 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_con1_NT] + (memop(a));

#051               if (c + 0 < p->cost[_stmt_NT]) {

#052                    p->cost[_stmt_NT] = c + 0;

#053                    p->rule._stmt = 17;

#054               }

#055         }

#056         if ( /* stmt: ASGNI4(addr,SUBU4(mem,con1)) */

#057               RIGHT_CHILD(a)->op == 4422 /* SUBU4 */

#058         ) {

#059                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#060 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_con1_NT] + (memop(a));

#061               if (c + 0 < p->cost[_stmt_NT]) {

#062                    p->cost[_stmt_NT] = c + 0;

#063                    p->rule._stmt = 18;

#064               }

#065         }

#066         if ( /* stmt: ASGNI4(addr,ADDI4(mem,rc)) */

#067               RIGHT_CHILD(a)->op == 4405 /* ADDI4 */

#068         ) {

#069                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#070 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_rc_NT] + (memop(a));

#071               if (c + 0 < p->cost[_stmt_NT]) {

#072                    p->cost[_stmt_NT] = c + 0;

#073                    p->rule._stmt = 20;

#074               }

#075         }

#076         if ( /* stmt: ASGNI4(addr,SUBI4(mem,rc)) */

#077               RIGHT_CHILD(a)->op == 4421 /* SUBI4 */

#078         ) {

#079                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#080 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_rc_NT] + (memop(a));

#081               if (c + 0 < p->cost[_stmt_NT]) {

#082                    p->cost[_stmt_NT] = c + 0;

#083                    p->rule._stmt = 21;

#084               }

#085         }

#086         if ( /* stmt: ASGNI4(addr,BANDI4(mem,rc)) */

#087               RIGHT_CHILD(a)->op == 4485 /* BANDI4 */

#088         ) {

#089                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#090 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_rc_NT] + (memop(a));

#091               if (c + 0 < p->cost[_stmt_NT]) {

#092                    p->cost[_stmt_NT] = c + 0;

#093                    p->rule._stmt = 24;

#094               }

#095         }

#096         if ( /* stmt: ASGNI4(addr,BORI4(mem,rc)) */

#097               RIGHT_CHILD(a)->op == 4517 /* BORI4 */

#098         ) {

#099                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#100 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_rc_NT] + (memop(a));

#101               if (c + 0 < p->cost[_stmt_NT]) {

#102                    p->cost[_stmt_NT] = c + 0;

#103                   p->rule._stmt = 25;

#104               }

#105         }

#106         if ( /* stmt: ASGNI4(addr,BXORI4(mem,rc)) */

#107               RIGHT_CHILD(a)->op == 4533 /* BXORI4 */

#108         ) {

#109                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#110 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_rc_NT] + (memop(a));

#111               if (c + 0 < p->cost[_stmt_NT]) {

#112                    p->cost[_stmt_NT] = c + 0;

#113                    p->rule._stmt = 26;

#114               }

#115         }

#116         if ( /* stmt: ASGNI4(addr,BCOMI4(mem)) */

#117               RIGHT_CHILD(a)->op == 4501 /* BCOMI4 */

#118         ) {

#119                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#120 [_mem_NT] + (memop(a));

#121               if (c + 0 < p->cost[_stmt_NT]) {

#122                    p->cost[_stmt_NT] = c + 0;

#123                    p->rule._stmt = 30;

#124               }

#125         }

#126         if ( /* stmt: ASGNI4(addr,NEGI4(mem)) */

#127               RIGHT_CHILD(a)->op == 4293 /* NEGI4 */

#128         ) {

#129                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#130 [_mem_NT] + (memop(a));

#131               if (c + 0 < p->cost[_stmt_NT]) {

#132                    p->cost[_stmt_NT] = c + 0;

#133                    p->rule._stmt = 32;

#134               }

#135         }

#136         if ( /* stmt: ASGNI4(addr,LSHI4(mem,con5)) */

#137               RIGHT_CHILD(a)->op == 4437 /* LSHI4 */

#138         ) {

#139                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#140 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_con5_NT] + (memop(a));

#141               if (c + 0 < p->cost[_stmt_NT]) {

#142                    p->cost[_stmt_NT] = c + 0;

#143                     p->rule._stmt = 33;

#144               }

#145         }

#146         if ( /* stmt: ASGNI4(addr,LSHU4(mem,con5)) */

#147               RIGHT_CHILD(a)->op == 4438 /* LSHU4 */

#148         ) {

#149                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#150 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_con5_NT] + (memop(a));

#151               if (c + 0 < p->cost[_stmt_NT]) {

#152                    p->cost[_stmt_NT] = c + 0;

#153                    p->rule._stmt = 34;

#154               }

#155         }

#156         if ( /* stmt: ASGNI4(addr,RSHI4(mem,con5)) */

#157               RIGHT_CHILD(a)->op == 4469 /* RSHI4 */

#158         ) {

#159                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#160 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_con5_NT] + (memop(a));

#161               if (c + 0 < p->cost[_stmt_NT]) {

#162                    p->cost[_stmt_NT] = c + 0;

#163                    p->rule._stmt = 35;

#164               }

#165         }

#166         if ( /* stmt: ASGNI4(addr,RSHU4(mem,con5)) */

#167               RIGHT_CHILD(a)->op == 4470 /* RSHU4 */

#168         ) {

#169                c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(LEFT_CHILD(RIGHT_CHILD(a))->x.state))->cost

#170 [_mem_NT] + ((struct _state *)(RIGHT_CHILD(RIGHT_CHILD(a))->x.state))->cost[_con5_NT] + (memop(a));

#171               if (c + 0 < p->cost[_stmt_NT]) {

#172                    p->cost[_stmt_NT] = c + 0;

#173                    p->rule._stmt = 36;

#174               }

#175         }

#176         /* stmt: ASGNI4(addr,rc) */

#177          c = ((struct _state *)(LEFT_CHILD(a)->x.state))->cost[_addr_NT] + ((struct _state *)(RIGHT_CHILD(a)->x.state))->cost[_rc_NT] + 1;

#178         if (c + 0 < p->cost[_stmt_NT]) {

#179               p->cost[_stmt_NT] = c + 0;

#180               p->rule._stmt = 39;

#181         }

#182         break;

#183  ...

#184  

第 7 行创建一个节点的状态空间。

第 10 行根据节点的类型选择不同的操作，也就是进行指令选择。

由分析中间表示树可知，第一个节点是 ASGNI4 ，所以就运行到第 14 行那里。

第 15 行进行左子树递归处理。

第 16 行进行右子树递归处理。

接着下来的程序就会根据左子树和右子树的类型，从下面的语句里选择出合适的指令，

stmt: ASGNI4(VREGP,reg)

stmt: ASGNI4(addr,ADDI4(mem,con1))

stmt: ASGNI4(addr,ADDU4(mem,con1))

stmt: ASGNI4(addr,SUBI4(mem,con1))

stmt: ASGNI4(addr,SUBU4(mem,con1))

stmt: ASGNI4(addr,ADDI4(mem,rc))

stmt: ASGNI4(addr,SUBI4(mem,rc))

stmt: ASGNI4(addr,BANDI4(mem,rc))

stmt: ASGNI4(addr,BORI4(mem,rc))

stmt: ASGNI4(addr,BXORI4(mem,rc))

stmt: ASGNI4(addr,BCOMI4(mem))

stmt: ASGNI4(addr,NEGI4(mem))

stmt: ASGNI4(addr,LSHI4(mem,con5))

stmt: ASGNI4(addr,LSHU4(mem,con5))

stmt: ASGNI4(addr,RSHI4(mem,con5))

stmt: ASGNI4(addr,RSHU4(mem,con5))

stmt: ASGNI4(addr,rc)

 

由于中间表示就可以知道从上面的指令里是选择最后一条指令生成，所以在第 179 行里设置了这条指令的开销，第 180 行里设置指令编码为 39 。

通过这样的计算，就可以选择出合适的指令。有了这两个值，后面会通过其它函数来生成上面的目标代码，下一次再解释怎么样生成目标代码。