PR c/7102

["Eric Botcazou" <ebotcazou at libertysurf dot fr>]

Hello,

I'm investigating PR c/7102 and I narrowed down the problem to the
lack of conversion of (const_int -1) from a QImode operand to a
HImode operand of an unsigned division in optabs.c:expand_binop().

Now about one year ago Alexandre Oliva commited the following patch:


2001-04-12  Alexandre Oliva  <aoliva@redhat.com>

 * expmed.c (store_bit_field): Truncate CONST_INTs.
 (expand_mult_highpart, expand_divmod): Likewise.
 * expr.c (convert_modes, store_field): Likewise.
 * integrate.c (expand_inline_function): Use promote_mode() to
 determine whether to convert_modes() an argument as signed
 or unsigned.
 * optabs.c (expand_binop): Get CONST_INT operands
 sign-extended for their appropriate modes.
 * stmt.c (emit_case_nodes): Convert node values to the
 appropriate mode.
 (expand_end_case): Convert minval and range to the appropriate
 mode.
 * unroll.c (loop_iterations): Truncate abs_diff to the mode of
 the iteration variable.
 * varasm.c (immed_double_const): Don't require words to be
 narrower than host wide ints to properly sign-extend
 CONST_INTs.


The diff for optabs.c reads:


--- gcc/optabs.c 28 Mar 2001 11:03:56 -0000 1.91
+++ gcc/optabs.c 12 Apr 2001 03:41:36 -0000 1.92
@@ -723,17 +723,25 @@
  }
 
       /* In case the insn wants input operands in modes different from
-  the result, convert the operands.  */
+  the result, convert the operands.  It would seem that we
+  don't need to convert CONST_INTs, but we do, so that they're
+  a properly sign-extended for their modes.  */
 
-      if (GET_MODE (op0) != VOIDmode
-   && GET_MODE (op0) != mode0
+      if (GET_MODE (op0) != mode0
    && mode0 != VOIDmode)
- xop0 = convert_to_mode (mode0, xop0, unsignedp);
+ xop0 = convert_modes (mode0,
+         GET_MODE (op0) != VOIDmode
+         ? GET_MODE (op0)
+         : mode0,
+         xop0, unsignedp);
 
-      if (GET_MODE (xop1) != VOIDmode
-   && GET_MODE (xop1) != mode1
+      if (GET_MODE (xop1) != mode1
    && mode1 != VOIDmode)
- xop1 = convert_to_mode (mode1, xop1, unsignedp);
+ xop1 = convert_modes (mode1,
+         GET_MODE (op1) != VOIDmode
+         ? GET_MODE (op1)
+         : mode1,
+         xop1, unsignedp);

 
It seems to me that, contrary to what the comment states, CONST_INTs
are still not converted because the patch is a no-op.


Later, Alexandre commited another patch:


2001-05-06  Alexandre Oliva  <aoliva@redhat.com>

 * optabs.c (expand_binop): Sign-extend xop0 and xop1 from the
 widest mode in narrowing and widening operations.


--- gcc/optabs.c 14 Apr 2001 03:39:22 -0000 1.93
+++ gcc/optabs.c 6 May 2001 19:47:15 -0000 1.94
@@ -725,13 +725,20 @@
       /* In case the insn wants input operands in modes different from
   the result, convert the operands.  It would seem that we
   don't need to convert CONST_INTs, but we do, so that they're
-  a properly sign-extended for their modes.  */
+  a properly sign-extended for their modes; we choose the
+  widest mode between mode and mode[01], so that, in a widening
+  operation, we call convert_modes with different FROM and TO
+  modes, which ensures the value is sign-extended.  Shift
+  operations are an exception, because the second operand needs
+  not be extended to the mode of the result.  */
 
       if (GET_MODE (op0) != mode0
    && mode0 != VOIDmode)
  xop0 = convert_modes (mode0,
          GET_MODE (op0) != VOIDmode
          ? GET_MODE (op0)
+         : GET_MODE_SIZE (mode) > GET_MODE_SIZE (mode0)
+         ? mode
          : mode0,
          xop0, unsignedp);
 
@@ -740,6 +747,9 @@
  xop1 = convert_modes (mode1,
          GET_MODE (op1) != VOIDmode
          ? GET_MODE (op1)
+         : (GET_MODE_SIZE (mode) > GET_MODE_SIZE (mode1)
+     && ! shift_op)
+         ? mode
          : mode1,
          xop1, unsignedp);


It seems that Alexandre noticed the problem, but the fix enables truncation
only, neither zero- nor sign-extension. Hence my question: is there anything
that forbids full conversion of the operands in that situation ?

--
Eric Botcazou
ebotcazou@multimania.com