(scm_is_pair): Add a workaround for i386 gcc 2.95 bad code generation.

libguile/inline.h

@@ -248,6 +248,27 @@ SCM_C_INLINE
 int
 scm_is_pair (SCM x)
 {
+  /* The following "workaround_for_gcc_295" avoids bad code generated by
+     i386 gcc 2.95.4 (the Debian packaged 2.95.4-24 at least).
+
+     Under the default -O2 the inlined SCM_I_CONSP test gets "optimized" so
+     the fetch of the tag word from x is done before confirming it's a
+     non-immediate (SCM_NIMP).  Needless to say that bombs badly if x is a
+     immediate.  This was seen to afflict scm_srfi1_split_at and something
+     deep in the bowels of ceval().  In both cases segvs resulted from
+     deferencing a random immediate value.  srfi-1.test exposes the problem
+     through a short list, the immediate being SCM_EOL in that case.
+     Something in syntax.test exposed the ceval() problem.
+
+     Just "volatile SCM workaround_for_gcc_295 = lst" is enough to avoid the
+     problem, without even using that variable.  The "w=w" is just to
+     prevent a warning about it being unused.
+     */
+#if defined (__GNUC__) && __GNUC__ == 2 && __GNUC_MINOR__ == 95
+  volatile SCM workaround_for_gcc_295 = x;
+  workaround_for_gcc_295 = workaround_for_gcc_295;
+#endif
+
   return SCM_I_CONSP (x);
 }