Make some smallest_int_mode_for_size calls cope with failure

smallest_int_mode_for_size now returns an optional mode rather
than aborting on failure.  This patch adjusts a couple of callers
so that they fail gracefully when no mode exists.

There should be no behavioural change, since anything that triggers
the new return paths would previously have aborted.  I just think
this is how the code would have been written if the option had been
available earlier.

gcc/
	* dse.cc (find_shift_sequence): Allow smallest_int_mode_for_size
	to failure.
	* optabs.cc (expand_twoval_binop_libfunc): Likewise.

diff --git a/gcc/dse.cc b/gcc/dse.cc
index c3feff06f864939a1936596260800ba4233488a3..75825a44cb98f02ca10b9a287c4824c62be80e7d 100644 (file)
--- a/gcc/dse.cc
+++ b/gcc/dse.cc
@@ -1717,12 +1717,12 @@ dump_insn_info (const char * start, insn_info_t insn_info)
    line up, we need to extract the value from lower part of the rhs of
    the store, shift it, and then put it into a form that can be shoved
    into the read_insn.  This function generates a right SHIFT of a
-   value that is at least ACCESS_SIZE bytes wide of READ_MODE.  The
+   value that is at least ACCESS_BYTES bytes wide of READ_MODE.  The
    shift sequence is returned or NULL if we failed to find a
    shift.  */
 
 static rtx
-find_shift_sequence (poly_int64 access_size,
+find_shift_sequence (poly_int64 access_bytes,
                     store_info *store_info,
                     machine_mode read_mode,
                     poly_int64 shift, bool speed, bool require_cst)
@@ -1734,11 +1734,11 @@ find_shift_sequence (poly_int64 access_size,
   /* If a constant was stored into memory, try to simplify it here,
      otherwise the cost of the shift might preclude this optimization
      e.g. at -Os, even when no actual shift will be needed.  */
+  auto access_bits = access_bytes * BITS_PER_UNIT;
   if (store_info->const_rhs
-      && known_le (access_size, GET_MODE_SIZE (MAX_MODE_INT)))
+      && known_le (access_bytes, GET_MODE_SIZE (MAX_MODE_INT))
+      && smallest_int_mode_for_size (access_bits).exists (&new_mode))
     {
-      auto new_mode = smallest_int_mode_for_size
-       (access_size * BITS_PER_UNIT).require ();
       auto byte = subreg_lowpart_offset (new_mode, store_mode);
       rtx ret
        = simplify_subreg (new_mode, store_info->const_rhs, store_mode, byte);
@@ -1810,7 +1810,7 @@ find_shift_sequence (poly_int64 access_size,
            }
        }
 
-      if (maybe_lt (GET_MODE_SIZE (new_mode), access_size))
+      if (maybe_lt (GET_MODE_SIZE (new_mode), access_bytes))
        continue;
 
       new_reg = gen_reg_rtx (new_mode);
@@ -1839,8 +1839,8 @@ find_shift_sequence (poly_int64 access_size,
         of the arguments and could be precomputed.  It may
         not be worth doing so.  We could precompute if
         worthwhile or at least cache the results.  The result
-        technically depends on both SHIFT and ACCESS_SIZE,
-        but in practice the answer will depend only on ACCESS_SIZE.  */
+        technically depends on both SHIFT and ACCESS_BYTES,
+        but in practice the answer will depend only on ACCESS_BYTES.  */
 
       if (cost > COSTS_N_INSNS (1))
        continue;

diff --git a/gcc/optabs.cc b/gcc/optabs.cc
index ded9cc3d947a860de0bdf869d52abc219de5bcb6..2bcb3f7b47aefbb12c26532229260840556ddcbc 100644 (file)
--- a/gcc/optabs.cc
+++ b/gcc/optabs.cc
@@ -2551,8 +2551,10 @@ expand_twoval_binop_libfunc (optab binoptab, rtx op0, rtx op1,
 
   /* The value returned by the library function will have twice as
      many bits as the nominal MODE.  */
-  libval_mode
-    = smallest_int_mode_for_size (2 * GET_MODE_BITSIZE (mode)).require ();
+  auto return_size = 2 * GET_MODE_BITSIZE (mode);
+  if (!smallest_int_mode_for_size (return_size).exists (&libval_mode))
+    return false;
+
   start_sequence ();
   libval = emit_library_call_value (libfunc, NULL_RTX, LCT_CONST,
                                    libval_mode,