In some cases, the code is fine, but GCC isn't smart enough to

figure that out; this usually happens when one variable is only
initialized and used when a particular condition holds true, and
we know that condition will never change within a given invocation
of the function.  In this case, we simply initialize the variables
to placate the compiler, hopefully to a value which will cause a
crash if it is ever actually used.
* print.c (scm_iprin1): Initialize mw_pos.
* read.c (scm_lreadrecparen): Initialize tl2, ans2.
* throw.c (scm_ithrow): Initialize dynpair.
* unif.c (scm_uniform_vector_ref): Initialize cra.
* struct.c (init_struct): Initialize prot.
* mbstrings.c (scm_print_mb_symbol): Initialize mw_pos and inc.

libguile/mbstrings.c

@@ -383,8 +383,8 @@ scm_print_mb_symbol (exp, port)
   char * str;
   int weird;
   int maybe_weird;
-  int mw_pos;
+  int mw_pos = 0;		/* initialized to placate compiler */
-  int inc;
+  int inc = 0;			/* same */
   xwchar_t c;
 
   len = SCM_LENGTH (exp);

libguile/print.c

@@ -411,7 +411,7 @@ taloop:
 	      char * str;
 	      int weird;
 	      int maybe_weird;
-	      int mw_pos;
+	      int mw_pos = 0;
 
 	      len = SCM_LENGTH (exp);
 	      str = SCM_CHARS (exp);

libguile/read.c

@@ -696,8 +696,8 @@ scm_lreadrecparen (tok_buf, port, name, case_i, sharp, copy)
 {
   register int c;
   register SCM tmp;
-  register SCM tl, tl2;
+  register SCM tl, tl2 = SCM_EOL;
-  SCM ans, ans2;
+  SCM ans, ans2 = SCM_EOL;
   /* Need to capture line and column numbers here. */
   int line = SCM_LINUM (port);
   int column = SCM_COL (port) - 1;

libguile/throw.c

@@ -389,7 +389,7 @@ scm_ithrow (key, args, noreturn)
     }
   else
     {
-      SCM dynpair;
+      SCM dynpair = SCM_UNDEFINED;
       SCM winds;
 
       if (noreturn)