code review 6547064: cmd/8g: don't create redundant temporaries in bgen.

src/cmd/8g/cgen.c

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // TODO(rsc):
 //      assume CLD?
 
 #include <u.h>
 #include <libc.h>
 #include "gg.h"
@@ skipping 1073 matching lines @@
                                 cgen(nr, &n2);
                                 nr = &n2;
                         }
                         cmp64(nl, nr, a, likely, to);
                         break;
                 }
 
                 a = optoas(a, nr->type);
 
                 if(nr->ullman >= UINF) {
-                        tempname(&n1, nl->type);
-                        tempname(&tmp, nr->type);
-                        cgen(nl, &n1);
-                        cgen(nr, &tmp);
+                        if(!nl->addable) {
+                                tempname(&n1, nl->type);
+                                cgen(nl, &n1);
+                                nl = &n1;
+                        }
+                        if(!nr->addable) {
+                                tempname(&tmp, nr->type);
+                                cgen(nr, &tmp);
+                                nr = &tmp;
+                        }
                         regalloc(&n2, nr->type, N);
-                        cgen(&tmp, &n2);
+                        cgen(nr, &n2);
                         goto cmp;
                 }
 
-                tempname(&n1, nl->type);
-                cgen(nl, &n1);
+                if(!nl->addable) {
+                        tempname(&n1, nl->type);
+                        cgen(nl, &n1);
+                        nl = &n1;
+                }
 
                 if(smallintconst(nr)) {
-                        gins(optoas(OCMP, nr->type), &n1, nr);
+                        gins(optoas(OCMP, nr->type), nl, nr);
                         patch(gbranch(a, nr->type, likely), to);
                         break;
                 }
 
-                tempname(&tmp, nr->type);
-                cgen(nr, &tmp);
+                if(!nr->addable) {
+                        tempname(&tmp, nr->type);
+                        cgen(nr, &tmp);
+                        nr = &tmp;
+                }
                 regalloc(&n2, nr->type, N);
-                gmove(&tmp, &n2);
+                gmove(nr, &n2);
 
 cmp:
-                gins(optoas(OCMP, nr->type), &n1, &n2);
+                gins(optoas(OCMP, nr->type), nl, &n2);
                 patch(gbranch(a, nr->type, likely), to);
                 regfree(&n2);
                 break;
         }
 }
 
 /*
  * n is on stack, either local variable
  * or return value from function call.
  * return n's offset from SP.
@@ skipping 310 matching lines @@
                 regfree(&nodl);
         return 0;
 
 yes:
         if(freer)
                 regfree(&nodr);
         if(freel)
                 regfree(&nodl);
         return 1;
 }