obstack: Work around ICE with Oracle Developer Studio 12.6 cc

obstack: Work around ICE with Oracle Developer Studio 12.6 cc

[Bruno Haible]

The Oracle Developer Studio 12.6 produces a compilation error when
compiling the Gnulib module 'obstack':

cc -m64 -O -DHAVE_CONFIG_H -I. -I../../gllib -I..  -DGNULIB_STRICT_CHECKING=1 -I/home/haible/prefix64/include  -g -c -o obstack.o ../../gllib/obstack.c
"../../gllib/obstack.c", line 119: internal compiler error: ir_process_arrloc_tree: bad arrloc tree
cc: acomp failed for ../../gllib/obstack.c
gmake[3]: *** [Makefile:1028: obstack.o] Error 2

The Oracle support determined that the problem is that the compiler gets
confused by the conditional expression in the __PTR_ALIGN macro.

This patch provides a workaround: Let's evaluate the condition at
configure time, rather than at compile time.


2024-03-27  Bruno Haible  <bruno@clisp.org>

	obstack: Work around ICE with Oracle cc 12.6 (regr. 2023-12-01).
	* lib/obstack.in.h (__PTR_ALIGN): Use SMALL_PTRDIFF_T, instead of
	testing sizeof (ptrdiff_t) < sizeof (void *) at compile time.
	* m4/obstack.m4 (gl_FUNC_OBSTACK): Set SMALL_PTRDIFF_T.
	* modules/obstack (Makefile.am): Substitute SMALL_PTRDIFF_T.

diff --git a/lib/obstack.in.h b/lib/obstack.in.h
index cf149947be..28fb4d8916 100644
--- a/lib/obstack.in.h
+++ b/lib/obstack.in.h
@@ -133,17 +133,19 @@
 # define _OBSTACK_CAST(type, expr) (expr)
 #endif
 
-/* If B is the base of an object addressed by P, return the result of
-   aligning P to the next multiple of A + 1.  B and P must be of type
-   char *.  A + 1 must be a power of 2.
+/* __PTR_ALIGN(B, P, A) returns the result of aligning P to the next multiple
+   of A + 1.  B must be the base of an object addressed by P.  B and P must be
+   of type char *.  A + 1 must be a power of 2.
    If ptrdiff_t is narrower than a pointer (e.g., the AS/400), play it
    safe and compute the alignment relative to B.  Otherwise, use the
    faster strategy of computing the alignment through uintptr_t.  */
-
-#define __PTR_ALIGN(B, P, A) \
-  (sizeof (ptrdiff_t) < sizeof (void *) \
-   ? (B) + (((P) - (B) + (A)) & ~(A))   \
-   : (P) + ((- (uintptr_t) (P)) & (A)))
+#if @SMALL_PTRDIFF_T@
+# define __PTR_ALIGN(B, P, A) \
+   ((B) + (((P) - (B) + (A)) & ~(A)))
+#else
+# define __PTR_ALIGN(B, P, A) \
+   ((P) + ((- (uintptr_t) (P)) & (A)))
+#endif
 
 #ifndef __attribute_pure__
 # define __attribute_pure__ _GL_ATTRIBUTE_PURE
diff --git a/m4/obstack.m4 b/m4/obstack.m4
index 196609d7fb..be553cfb78 100644
--- a/m4/obstack.m4
+++ b/m4/obstack.m4
@@ -45,4 +45,25 @@ AC_DEFUN([gl_FUNC_OBSTACK]
     GL_GENERATE_OBSTACK_H=false
   fi
   AC_SUBST([REPLACE_OBSTACK])
+
+  dnl Test whether a 'ptrdiff_t' has at least as many bits as a pointer.
+  AC_CACHE_CHECK([whether ptrdiff_t is at least as large as a pointer],
+    [gl_cv_ptrdiff_t_wide_enough],
+    [AC_COMPILE_IFELSE(
+       [AC_LANG_PROGRAM(
+          [[#include <stddef.h>
+            typedef int check[2 * (sizeof (ptrdiff_t) >= sizeof (void *)) - 1];
+           ]],
+          [[]])],
+       [gl_cv_ptrdiff_t_wide_enough=yes],
+       [gl_cv_ptrdiff_t_wide_enough=no])
+    ])
+  if test $gl_cv_ptrdiff_t_wide_enough = yes; then
+    SMALL_PTRDIFF_T=0
+  else
+    SMALL_PTRDIFF_T=1
+  fi
+  dnl SMALL_PTRDIFF_T is expected to be 1 only on old / exotic platforms
+  dnl such as Windows 3.1 and AS/400.
+  AC_SUBST([SMALL_PTRDIFF_T])
 ])
diff --git a/modules/obstack b/modules/obstack
index e4db4cdc97..5c94894e8c 100644
--- a/modules/obstack
+++ b/modules/obstack
@@ -31,6 +31,7 @@ obstack.h: obstack.in.h $(top_builddir)/config.status
 @NMD@	$(AM_V_GEN)$(MKDIR_P) '%reldir%'
 	$(gl_V_at)$(SED_HEADER_STDOUT) \
 	      -e 's|@''REPLACE_OBSTACK''@|$(REPLACE_OBSTACK)|g' \
+	      -e 's|@''SMALL_PTRDIFF_T''@|$(SMALL_PTRDIFF_T)|g' \
 	      $(srcdir)/obstack.in.h > $@-t
 	$(AM_V_at)mv $@-t $@
 else