Re: RFA: Fix mode checks for possibly-constant predicates

[Richard Sandiford <richard dot sandiford at arm dot com>]

Richard Henderson <rth@redhat.com> writes:
> On 05/29/2015 10:23 AM, Richard Sandiford wrote:
>> +  /* Check whether the predicate accepts const scalar ints (which always
>> +     have a stored mode of VOIDmode, but logically have a real mode)
>> +     and whether it matches anything besides const scalar ints.  */
>> +  bool matches_const_scalar_int_p = false;
>> +  bool matches_other_p = false;
>> +  for (int i = 0; i < NUM_RTX_CODE; ++i)
>> +    if (p->codes[i])
>> +      switch (i)
>> +	{
>> +	CASE_CONST_SCALAR_INT:
>> +	  matches_const_scalar_int_p = true;
>> +	  break;
>> +
>> +	default:
>> +	  matches_other_p = true;
>> +	  break;
>> +	}
>> +
>> +  /* There's no need for a mode check if the predicate only accepts
>> +     constant integers.  The code checks in the predicate are enough
>> +     to establish that the mode is VOIDmode.
>> +
>> +     Note that the predicate itself should check whether a scalar
>> +     integer is in range of the given mode.  */
>> +  if (!matches_other_p && !p->codes[CONST_DOUBLE])
>> +    return;
>
> I think perhaps it would be cleaner to not use CASE_CONST_SCALAR_INT,
> and then do
>
>   switch (i)
>     {
>     case CONST_INT:
>     case CONST_WIDE_INT:
>       matches_const_scalar_int_p = true;
>       break;
>
>     case CONST_DOUBLE:
>       if (!TARGET_SUPPORTS_WIDE_INT)
>         matches_const_scalar_int_p = true;
>       matches_other_p = true;
>       break;
>
>     default:
>       matches_other_p = true;
>       break;
>     }
>
>   if (!matches_other_p)
>     return;
>
> Otherwise ok.

Ah, yeah, that's better.  Here's what I applied after testing on
x86_64-linux-gnu.

Thanks,
Richard


gcc/
	* genpreds.c (mark_mode_tests): Mark all MATCH_CODEs as
	NO_MODE_TEST.
	(add_mode_tests): Don't add mode tests if the predicate only
	accepts scalar constant integers.  Otherwise, allow the mode
	of "op" to be VOIDmode if the predicate does accept such integers.

Index: gcc/genpreds.c
===================================================================
--- gcc/genpreds.c	2015-06-02 13:32:21.394938060 +0100
+++ gcc/genpreds.c	2015-06-02 13:34:50.377221396 +0100
@@ -218,11 +218,11 @@ needs_variable (rtx exp, const char *var
 
 /* Given an RTL expression EXP, find all subexpressions which we may
    assume to perform mode tests.  Normal MATCH_OPERAND does;
-   MATCH_CODE does if it applies to the whole expression and accepts
-   CONST_INT or CONST_DOUBLE; and we have to assume that MATCH_TEST
-   does not.  These combine in almost-boolean fashion - the only
-   exception is that (not X) must be assumed not to perform a mode
-   test, whether or not X does.
+   MATCH_CODE doesn't as such (although certain codes always have
+   VOIDmode); and we have to assume that MATCH_TEST does not.
+   These combine in almost-boolean fashion - the only exception is
+   that (not X) must be assumed not to perform a mode test, whether
+   or not X does.
 
    The mark is the RTL /v flag, which is true for subexpressions which
    do *not* perform mode tests.
@@ -244,10 +244,7 @@ mark_mode_tests (rtx exp)
       break;
 
     case MATCH_CODE:
-      if (XSTR (exp, 1)[0] != '\0'
-	  || (!strstr (XSTR (exp, 0), "const_int")
-	      && !strstr (XSTR (exp, 0), "const_double")))
-	NO_MODE_TEST (exp) = 1;
+      NO_MODE_TEST (exp) = 1;
       break;
 
     case MATCH_TEST:
@@ -313,6 +310,40 @@ add_mode_tests (struct pred_data *p)
   if (p->special)
     return;
 
+  /* Check whether the predicate accepts const scalar ints (which always
+     have a stored mode of VOIDmode, but logically have a real mode)
+     and whether it matches anything besides const scalar ints.  */
+  bool matches_const_scalar_int_p = false;
+  bool matches_other_p = false;
+  for (int i = 0; i < NUM_RTX_CODE; ++i)
+    if (p->codes[i])
+      switch (i)
+	{
+	case CONST_INT:
+	case CONST_WIDE_INT:
+	  matches_const_scalar_int_p = true;
+	  break;
+
+	case CONST_DOUBLE:
+	  if (!TARGET_SUPPORTS_WIDE_INT)
+	    matches_const_scalar_int_p = true;
+	  matches_other_p = true;
+	  break;
+
+	default:
+	  matches_other_p = true;
+	  break;
+	}
+
+  /* There's no need for a mode check if the predicate only accepts
+     constant integers.  The code checks in the predicate are enough
+     to establish that the mode is VOIDmode.
+
+     Note that the predicate itself should check whether a scalar
+     integer is in range of the given mode.  */
+  if (!matches_other_p)
+    return;
+
   mark_mode_tests (p->exp);
 
   /* If the whole expression already tests the mode, we're done.  */
@@ -320,7 +351,11 @@ add_mode_tests (struct pred_data *p)
     return;
 
   match_test_exp = rtx_alloc (MATCH_TEST);
-  XSTR (match_test_exp, 0) = "mode == VOIDmode || GET_MODE (op) == mode";
+  if (matches_const_scalar_int_p)
+    XSTR (match_test_exp, 0) = ("mode == VOIDmode || GET_MODE (op) == mode"
+				" || GET_MODE (op) == VOIDmode");
+  else
+    XSTR (match_test_exp, 0) = "mode == VOIDmode || GET_MODE (op) == mode";
   and_exp = rtx_alloc (AND);
   XEXP (and_exp, 1) = match_test_exp;