diff mbox series

constraint: fix relaxed memory and repeated constraint handling

Message ID yw8jfsb5fzx9.fsf@arm.com
State Accepted
Headers
Series constraint: fix relaxed memory and repeated constraint handling |

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Context Check Description
snail/gcc-patch-check success Github commit url

Commit Message

Victor Do Nascimento Feb. 16, 2023, 2:27 p.m. UTC 
  The function `constrain_operands' lacked the logic to consider relaxed
memory constraints when "traditional" memory constraints were not
satisfied, creating potential issues as observed during the reload
compilation pass.

In addition, it was observed that while `constrain_operands' chooses
to disregard constraints when more than one alternative is provided,
e.g. "m,r" using CONSTRAINT__UNKNOWN, it has no checks in place to
determine whether the multiple constraints in a given string are in
fact repetitions of the same constraint and should thus in fact be
treated as a single constraint, as ought to be the case for something
like "m,m".

Both of these issues are dealt with here, thus ensuring that we get
appropriate pattern matching.

Tested on aarch64-linux-gnu & x86_64-linux-gnu.  OK to install?

Victor

gcc/
	* lra-constraints.cc (constraint_unique): New.
	(process_address_1): Apply constraint_unique test.
	* recog.cc (constrain_operands): Allow relaxed memory
	constaints.
---
 gcc/lra-constraints.cc | 43 +++++++++++++++++++++++++++++++++++++++---
 gcc/recog.cc           |  3 ++-
 2 files changed, 42 insertions(+), 4 deletions(-)

Comments

Richard Sandiford Feb. 27, 2023, 2:29 p.m. UTC | #1 
"Victor L. Do Nascimento" <victor.donascimento@arm.com> writes:
> The function `constrain_operands' lacked the logic to consider relaxed
> memory constraints when "traditional" memory constraints were not
> satisfied, creating potential issues as observed during the reload
> compilation pass.
>
> In addition, it was observed that while `constrain_operands' chooses
> to disregard constraints when more than one alternative is provided,
> e.g. "m,r" using CONSTRAINT__UNKNOWN, it has no checks in place to
> determine whether the multiple constraints in a given string are in
> fact repetitions of the same constraint and should thus in fact be
> treated as a single constraint, as ought to be the case for something
> like "m,m".
>
> Both of these issues are dealt with here, thus ensuring that we get
> appropriate pattern matching.
>
> Tested on aarch64-linux-gnu & x86_64-linux-gnu.  OK to install?
>
> Victor
>
> gcc/
> 	* lra-constraints.cc (constraint_unique): New.
> 	(process_address_1): Apply constraint_unique test.
> 	* recog.cc (constrain_operands): Allow relaxed memory
> 	constaints.
> ---
>  gcc/lra-constraints.cc | 43 +++++++++++++++++++++++++++++++++++++++---
>  gcc/recog.cc           |  3 ++-
>  2 files changed, 42 insertions(+), 4 deletions(-)
>
> diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
> index dbfaf0485..c9c1653c0 100644
> --- a/gcc/lra-constraints.cc
> +++ b/gcc/lra-constraints.cc
> @@ -3448,6 +3448,45 @@ skip_constraint_modifiers (const char *str)
>        }
>  }
>  
> +/*  Takes a string of 0 or more comma-separated constraints and the
> +    constraint_num correspondig to the first constraint.  When more
> +    than one constraint present, evaluate whether they all correspond
> +    to a single, repeated constraint (e.g. "r,r") or whether we have
> +    more than one distinct constraints (e.g. "r,m").  */

Minor formatting nit: indentation should be to "/* " rather than "/*  ".

> +static bool
> +constraint_unique (const char *cstr, enum constraint_num ca)
> +{
> +   enum constraint_num cb;
> +   for (;;)
> +     {
> +       /* Skip past current constraint and any whitespace which may
> +	  precede the end-of-line or separator characters.  */
> +       cstr = skip_constraint_modifiers (cstr
> +					 + CONSTRAINT_LEN (cstr[0], cstr));
> +       /* If end of string reached and no disagreement found, we have
> +	  uniqueness.  */
> +       if (*cstr == '\0')
> +	 return true;
> +       /* skip_constraint_modifiers does not handle commas, handle
> +	  case manually.  */
> +       if (*cstr == ',')
> +	 cstr++;
> +       /* Get next constraint.  */
> +       cstr =  skip_constraint_modifiers (cstr);
> +       cb = lookup_constraint ((*cstr == '\0' || *cstr == ',') ? "X" : cstr);
> +
> +       /* If mismatch found, break out of loop.  */
> +       if (cb != ca)
> +	 return false;
> +
> +       /* If *cstr == '\0', we don't want to reach the
> +	  skip_constraint_modifiers statement again as that will
> +	  advance the pointer past the end of the string.  */
> +       if (*cstr == '\0')
> +	 return true;
> +     }
> +}

How about rearranging this a bit to something like:

  ca = CONSTRAINT__UNKNOWN;
  for (;;)
    {
      cstr = skip_constraint_modifiers (cstr);
      if (*cstr == '\0' || *cstr == ',')
        cb = CONSTRAINT_X;
      else
        {
          cb = lookup_constraint (cstr);
          if (cb == CONSTRAINT__UNKNOWN)
            return false;
          cstr += CONSTRAINT_LEN (cstr[0], cstr);
        }
      if (ca == CONSTRAINT__UNKNOWN)
        ca = cb
      else if (ca != cb)
        return false;
      if (*cstr == '\0')
        return true;
      if (*cstr == ',')
        cstr += 1;
    }

That way we only do one lookup per loop iteration.  It also avoids
CONSTRAINT_LEN for the "empty, followed by comma" case.

If that works, the patch is OK with those changes once another
approved-for-GCC-13 patch needs it.  OK for GCC 14 otherwise.

Thanks,
Richard

> +
>  /* Major function to make reloads for an address in operand NOP or
>     check its correctness (If CHECK_ONLY_P is true). The supported
>     cases are:
> @@ -3507,9 +3546,7 @@ process_address_1 (int nop, bool check_only_p,
>       operand has one address constraint, probably all others constraints are
>       address ones.  */
>    if (constraint[0] != '\0' && get_constraint_type (cn) != CT_ADDRESS
> -      && *skip_constraint_modifiers (constraint
> -				     + CONSTRAINT_LEN (constraint[0],
> -						       constraint)) != '\0')
> +      && !constraint_unique (constraint, cn))
>      cn = CONSTRAINT__UNKNOWN;
>    if (insn_extra_address_constraint (cn)
>        /* When we find an asm operand with an address constraint that
> diff --git a/gcc/recog.cc b/gcc/recog.cc
> index 200cf4214..3ddeab59d 100644
> --- a/gcc/recog.cc
> +++ b/gcc/recog.cc
> @@ -3234,7 +3234,8 @@ constrain_operands (int strict, alternative_mask alternatives)
>  		  else if (constraint_satisfied_p (op, cn))
>  		    win = 1;
>  
> -		  else if (insn_extra_memory_constraint (cn)
> +		  else if ((insn_extra_memory_constraint (cn)
> +			    || insn_extra_relaxed_memory_constraint (cn))
>  			   /* Every memory operand can be reloaded to fit.  */
>  			   && ((strict < 0 && MEM_P (op))
>  			       /* Before reload, accept what reload can turn
diff mbox series

Patch

diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index dbfaf0485..c9c1653c0 100644
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -3448,6 +3448,45 @@  skip_constraint_modifiers (const char *str)
       }
 }
 
+/*  Takes a string of 0 or more comma-separated constraints and the
+    constraint_num correspondig to the first constraint.  When more
+    than one constraint present, evaluate whether they all correspond
+    to a single, repeated constraint (e.g. "r,r") or whether we have
+    more than one distinct constraints (e.g. "r,m").  */
+static bool
+constraint_unique (const char *cstr, enum constraint_num ca)
+{
+   enum constraint_num cb;
+   for (;;)
+     {
+       /* Skip past current constraint and any whitespace which may
+	  precede the end-of-line or separator characters.  */
+       cstr = skip_constraint_modifiers (cstr
+					 + CONSTRAINT_LEN (cstr[0], cstr));
+       /* If end of string reached and no disagreement found, we have
+	  uniqueness.  */
+       if (*cstr == '\0')
+	 return true;
+       /* skip_constraint_modifiers does not handle commas, handle
+	  case manually.  */
+       if (*cstr == ',')
+	 cstr++;
+       /* Get next constraint.  */
+       cstr =  skip_constraint_modifiers (cstr);
+       cb = lookup_constraint ((*cstr == '\0' || *cstr == ',') ? "X" : cstr);
+
+       /* If mismatch found, break out of loop.  */
+       if (cb != ca)
+	 return false;
+
+       /* If *cstr == '\0', we don't want to reach the
+	  skip_constraint_modifiers statement again as that will
+	  advance the pointer past the end of the string.  */
+       if (*cstr == '\0')
+	 return true;
+     }
+}
+
 /* Major function to make reloads for an address in operand NOP or
    check its correctness (If CHECK_ONLY_P is true). The supported
    cases are:
@@ -3507,9 +3546,7 @@  process_address_1 (int nop, bool check_only_p,
      operand has one address constraint, probably all others constraints are
      address ones.  */
   if (constraint[0] != '\0' && get_constraint_type (cn) != CT_ADDRESS
-      && *skip_constraint_modifiers (constraint
-				     + CONSTRAINT_LEN (constraint[0],
-						       constraint)) != '\0')
+      && !constraint_unique (constraint, cn))
     cn = CONSTRAINT__UNKNOWN;
   if (insn_extra_address_constraint (cn)
       /* When we find an asm operand with an address constraint that
diff --git a/gcc/recog.cc b/gcc/recog.cc
index 200cf4214..3ddeab59d 100644
--- a/gcc/recog.cc
+++ b/gcc/recog.cc
@@ -3234,7 +3234,8 @@  constrain_operands (int strict, alternative_mask alternatives)
 		  else if (constraint_satisfied_p (op, cn))
 		    win = 1;
 
-		  else if (insn_extra_memory_constraint (cn)
+		  else if ((insn_extra_memory_constraint (cn)
+			    || insn_extra_relaxed_memory_constraint (cn))
 			   /* Every memory operand can be reloaded to fit.  */
 			   && ((strict < 0 && MEM_P (op))
 			       /* Before reload, accept what reload can turn