This patch uses GET_MODE_UNIT_SIZE instead of GET_MODE_SIZE in
cases where, for compound modes, the mode of the scalar elements
is what matters.  E.g. the choice between truncation and extension
is really based on the modes of the consistuent scalars rather
than the mode as a whole.

None of the existing code was wrong.  The patch simply makes
things easier when converting to variable-sized modes.

Tested on aarch64-linux-gnu and x86_64-linux-gnu, and by making sure
that there were no differences in testsuite assembly output for one
target per CPU.  OK to install?

Richard


2017-08-22  Richard Sandiford  <richard.sandif...@linaro.org>
            Alan Hayward  <alan.hayw...@arm.com>
            David Sherwood  <david.sherw...@arm.com>

gcc/
        * optabs.c (add_equal_note): Use GET_MODE_UNIT_SIZE.
        (widened_mode): Likewise.
        (expand_unop): Likewise.
        * ree.c (transform_ifelse): Likewise.
        (merge_def_and_ext): Likewise.
        (combine_reaching_defs): Likewise.
        * simplify-rtx.c (simplify_unary_operation_1): Likewise.

Index: gcc/optabs.c
===================================================================
--- gcc/optabs.c        2017-08-03 10:40:53.028490556 +0100
+++ gcc/optabs.c        2017-08-23 10:47:48.126586565 +0100
@@ -138,8 +138,8 @@ add_equal_note (rtx_insn *insns, rtx tar
        if (GET_MODE (op0) != VOIDmode && GET_MODE (target) != GET_MODE (op0))
          {
            note = gen_rtx_fmt_e (code, GET_MODE (op0), copy_rtx (op0));
-           if (GET_MODE_SIZE (GET_MODE (op0))
-               > GET_MODE_SIZE (GET_MODE (target)))
+           if (GET_MODE_UNIT_SIZE (GET_MODE (op0))
+               > GET_MODE_UNIT_SIZE (GET_MODE (target)))
              note = simplify_gen_unary (TRUNCATE, GET_MODE (target),
                                         note, GET_MODE (op0));
            else
@@ -173,12 +173,12 @@ widened_mode (machine_mode to_mode, rtx
 
   if (m0 == VOIDmode && m1 == VOIDmode)
     return to_mode;
-  else if (m0 == VOIDmode || GET_MODE_SIZE (m0) < GET_MODE_SIZE (m1))
+  else if (m0 == VOIDmode || GET_MODE_UNIT_SIZE (m0) < GET_MODE_UNIT_SIZE (m1))
     result = m1;
   else
     result = m0;
 
-  if (GET_MODE_SIZE (result) > GET_MODE_SIZE (to_mode))
+  if (GET_MODE_UNIT_SIZE (result) > GET_MODE_UNIT_SIZE (to_mode))
     return to_mode;
 
   return result;
@@ -2982,9 +2982,9 @@ expand_unop (machine_mode mode, optab un
       else
        {
          eq_value = gen_rtx_fmt_e (optab_to_code (unoptab), mode, op0);
-         if (GET_MODE_SIZE (outmode) < GET_MODE_SIZE (mode))
+         if (GET_MODE_UNIT_SIZE (outmode) < GET_MODE_UNIT_SIZE (mode))
            eq_value = simplify_gen_unary (TRUNCATE, outmode, eq_value, mode);
-         else if (GET_MODE_SIZE (outmode) > GET_MODE_SIZE (mode))
+         else if (GET_MODE_UNIT_SIZE (outmode) > GET_MODE_UNIT_SIZE (mode))
            eq_value = simplify_gen_unary (ZERO_EXTEND,
                                           outmode, eq_value, mode);
        }
Index: gcc/ree.c
===================================================================
--- gcc/ree.c   2017-08-23 10:44:17.185477350 +0100
+++ gcc/ree.c   2017-08-23 10:47:48.126586565 +0100
@@ -427,7 +427,8 @@ transform_ifelse (ext_cand *cand, rtx_in
   srcreg2 = XEXP (SET_SRC (set_insn), 2);
   /* If the conditional move already has the right or wider mode,
      there is nothing to do.  */
-  if (GET_MODE_SIZE (GET_MODE (dstreg)) >= GET_MODE_SIZE (cand->mode))
+  if (GET_MODE_UNIT_SIZE (GET_MODE (dstreg))
+      >= GET_MODE_UNIT_SIZE (cand->mode))
     return true;
 
   map_srcreg = gen_rtx_REG (cand->mode, REGNO (srcreg));
@@ -717,8 +718,8 @@ merge_def_and_ext (ext_cand *cand, rtx_i
              && state->modified[INSN_UID (def_insn)].mode
                 == ext_src_mode)))
     {
-      if (GET_MODE_SIZE (GET_MODE (SET_DEST (*sub_rtx)))
-         >= GET_MODE_SIZE (cand->mode))
+      if (GET_MODE_UNIT_SIZE (GET_MODE (SET_DEST (*sub_rtx)))
+         >= GET_MODE_UNIT_SIZE (cand->mode))
        return true;
       /* If def_insn is already scheduled to be deleted, don't attempt
         to modify it.  */
@@ -926,7 +927,8 @@ combine_reaching_defs (ext_cand *cand, c
          || (set = single_set (cand->insn)) == NULL_RTX)
        return false;
       mode = GET_MODE (SET_DEST (set));
-      gcc_assert (GET_MODE_SIZE (mode) >= GET_MODE_SIZE (cand->mode));
+      gcc_assert (GET_MODE_UNIT_SIZE (mode)
+                 >= GET_MODE_UNIT_SIZE (cand->mode));
       cand->mode = mode;
     }
 
Index: gcc/simplify-rtx.c
===================================================================
--- gcc/simplify-rtx.c  2017-08-23 10:44:17.187477282 +0100
+++ gcc/simplify-rtx.c  2017-08-23 10:47:48.127582392 +0100
@@ -1266,10 +1266,9 @@ simplify_unary_operation_1 (enum rtx_cod
       if ((GET_CODE (op) == FLOAT_TRUNCATE
           && flag_unsafe_math_optimizations)
          || GET_CODE (op) == FLOAT_EXTEND)
-       return simplify_gen_unary (GET_MODE_SIZE (GET_MODE (XEXP (op,
-                                                           0)))
-                                  > GET_MODE_SIZE (mode)
-                                  ? FLOAT_TRUNCATE : FLOAT_EXTEND,
+       return simplify_gen_unary (GET_MODE_UNIT_SIZE (GET_MODE (XEXP (op, 0)))
+                                  > GET_MODE_UNIT_SIZE (mode)
+                                  ? FLOAT_TRUNCATE : FLOAT_EXTEND,
                                   mode,
                                   XEXP (op, 0), mode);
 

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