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Some wide-int review comments

Message ID 528D4649.5020804@naturalbridge.com
State New
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Kenneth Zadeck Nov. 20, 2013, 11:31 p.m. UTC 
On 11/13/2013 04:59 AM, Richard Biener wrote:
> On Tue, Nov 12, 2013 at 5:43 PM, Kenneth Zadeck
> <zadeck@naturalbridge.com> wrote:
>> On 11/12/2013 11:27 AM, Joseph S. Myers wrote:
>>> On Tue, 12 Nov 2013, Kenneth Zadeck wrote:
>>>
>>>> Richi,
>>>>
>>>> i am having a little trouble putting this back the way that you want.
>>>> The
>>>> issue is rem.
>>>> what is supposed to happen for INT_MIN % -1?
>>>>
>>>> I would assume because i am failing the last case of
>>>> gcc.dg/c90-const-expr-8.c
>>>> that INT_MIN %-1 should not overflow even if INT_MIN / -1 does.
>>>> however,
>>> Given the conclusion in C11 that a%b should be considered undefined if a/b
>>> is not representable, I think it's reasonable to say INT_MIN % -1 *should*
>>> be considered to overflow (for all C standard versions) (and bug 30484 is
>>> only a bug for -fwrapv).
>>>
>> however, my local question is what do we want the api to be
>> int-const-binop-1?    The existing behavior seems to be that at least for
>> common modes this function silently returns 0 and it is up to the front ends
>> to put their own spin on it.
> For wide-int you create 1:1 the behavior of current trunk (if a change of
> behavior in TImode is not tested in the testsuite then you can ignore that).
> Whatever change you do to semantics of functions you do separately
> from wide-int (preferably first on trunk, or at your choice after the wide-int
> merge).
>
> For this case in question I'd say a % -1 should return 0, but for
> INT_MIN % -1 that 0 should have TREE_OVERFLOW set (and
> thus you need to adjust that c90-const-expr-8.c testcase).
>
> Richard.
>
>> kenny
richi,
I have done this exactly as you suggested.   bootstrapped and regression 
tested on x86-64.

2013-11-20  Kenneth Zadeck  <zadeck@naturalbridge.com>

     * fold-const.c
     (int_const_binop_1): Make INT_MIN % -1 return 0 with the overflow
     bit set.


2013-11-20  Kenneth Zadeck  <zadeck@naturalbridge.com>

     * gcc.dg/c90-const-expr-8.c: Look for overflow on INT_MIN % -1.
     * gcc.dg/c99-const-expr-8.c: Look for overflow on INT_MIN % -1.

ok to commit?

kenny
diff mbox

Patch

Index: gcc/fold-const.c
===================================================================
--- gcc/fold-const.c	(revision 205161)
+++ gcc/fold-const.c	(working copy)
@@ -1105,7 +1105,22 @@  int_const_binop_1 (enum tree_code code,
     case ROUND_MOD_EXPR:
       if (op2.is_zero ())
 	return NULL_TREE;
-      tmp = op1.divmod_with_overflow (op2, uns, code, &res, &overflow);
+
+      /* Check for the case the case of INT_MIN % -1 and return
+       overflow and result = 0.  The TImode case is handled properly
+       in double-int.  */
+      if (TYPE_PRECISION (type) <= HOST_BITS_PER_WIDE_INT 
+	  && !uns
+          && op2.is_minus_one () 
+	  && op1.high == (HOST_WIDE_INT) -1
+	  && (HOST_WIDE_INT) op1.low 
+	  == (((HOST_WIDE_INT)-1) << (TYPE_PRECISION (type) - 1)))
+	{
+	  overflow = 1;
+	  res = double_int_zero;
+	}
+      else
+	tmp = op1.divmod_with_overflow (op2, uns, code, &res, &overflow);
       break;
 
     case MIN_EXPR:
Index: gcc/testsuite/gcc.dg/c90-const-expr-8.c
===================================================================
--- gcc/testsuite/gcc.dg/c90-const-expr-8.c	(revision 205161)
+++ gcc/testsuite/gcc.dg/c90-const-expr-8.c	(working copy)
@@ -23,5 +23,6 @@  enum e {
   /* { dg-error "3:overflow in constant expression" "constant" { target *-*-* } 22 } */
   E6 = 0 * !-INT_MIN, /* { dg-warning "13:integer overflow in expression" } */
   /* { dg-error "8:not an integer constant" "constant" { target *-*-* } 24 } */
-  E7 = INT_MIN % -1 /* Not an overflow.  */
+  E7 = INT_MIN % -1 /* { dg-warning "16:integer overflow in expression" } */
+  /* { dg-error "1:overflow in constant expression" "constant" { target *-*-* } 28 } */
 };
Index: gcc/testsuite/gcc.dg/c99-const-expr-8.c
===================================================================
--- gcc/testsuite/gcc.dg/c99-const-expr-8.c	(revision 205161)
+++ gcc/testsuite/gcc.dg/c99-const-expr-8.c	(working copy)
@@ -23,5 +23,6 @@  enum e {
   /* { dg-error "overflow in constant expression" "constant" { target *-*-* } 22 } */
   E6 = 0 * !-INT_MIN, /* { dg-warning "integer overflow in expression" } */
   /* { dg-error "not an integer constant" "constant" { target *-*-* } 24 } */
-  E7 = INT_MIN % -1 /* Not an overflow.  */
+  E7 = INT_MIN % -1 /* { dg-warning "16:integer overflow in expression" } */
+  /* { dg-error "1:overflow in constant expression" "constant" { target *-*-* } 28 } */
 };