Marc Glisse <marc.gli...@inria.fr> writes:
> On Fri, 20 Jul 2018, Richard Sandiford wrote:
>
>> --- gcc/match.pd 2018-07-18 18:44:22.565914281 +0100
>> +++ gcc/match.pd 2018-07-20 11:24:33.692045585 +0100
>> @@ -4924,3 +4924,37 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>> (if (inverse_conditions_p (@0, @2)
>> && element_precision (type) == element_precision (op_type))
>> (view_convert (cond_op @2 @3 @4 @5 (view_convert:op_type @1)))))))
>> +
>> +/* For pointers @0 and @2 and unsigned constant offset @1, look for
>> + expressions like:
>> +
>> + A: (@0 + @1 < @2) | (@2 + @1 < @0)
>> + B: (@0 + @1 <= @2) | (@2 + @1 <= @0)
>> +
>> + If pointers are known not to wrap, B checks whether @1 bytes starting at
>> + @0 and @2 do not overlap, while A tests the same thing for @1 + 1 bytes.
>> + A is more efficiently tested as:
>> +
>> + ((sizetype) @0 - (sizetype) @2 + @1) > (@1 * 2)
>> +
>> + as long as @1 * 2 doesn't overflow. B is the same with @1 replaced
>> + with @1 - 1. */
>> +(for ior (truth_orif truth_or bit_ior)
>> + (for cmp (le lt)
>> + (simplify
>> + (ior (cmp (pointer_plus:s @0 INTEGER_CST@1) @2)
>> + (cmp (pointer_plus:s @2 @1) @0))
>
> Do you want :c on cmp, in case it appears as @2 > @0 + @1 ? (may need some
> care with "cmp == LE_EXPR" below)
> Do you want :s on cmp as well?
>
>> + (if (!flag_trapv && !TYPE_OVERFLOW_WRAPS (TREE_TYPE (@0)))
>
> Don't you want TYPE_OVERFLOW_UNDEFINED?
Thanks, fixed below. Think the cmp == LE_EXPR stuff is still ok with :c,
since the generated code sets cmp to LE_EXPR when matching GE_EXPR.
Tested as before. OK to install?
Richard
2018-07-23 Richard Sandiford <richard.sandif...@arm.com>
gcc/
* match.pd: Optimise pointer range checks.
gcc/testsuite/
* gcc.dg/pointer-range-check-1.c: New test.
* gcc.dg/pointer-range-check-2.c: Likewise.
Index: gcc/match.pd
===================================================================
--- gcc/match.pd 2018-07-23 15:56:47.000000000 +0100
+++ gcc/match.pd 2018-07-23 15:58:33.480269844 +0100
@@ -4924,3 +4924,37 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(if (inverse_conditions_p (@0, @2)
&& element_precision (type) == element_precision (op_type))
(view_convert (cond_op @2 @3 @4 @5 (view_convert:op_type @1)))))))
+
+/* For pointers @0 and @2 and unsigned constant offset @1, look for
+ expressions like:
+
+ A: (@0 + @1 < @2) | (@2 + @1 < @0)
+ B: (@0 + @1 <= @2) | (@2 + @1 <= @0)
+
+ If pointers are known not to wrap, B checks whether @1 bytes starting at
+ @0 and @2 do not overlap, while A tests the same thing for @1 + 1 bytes.
+ A is more efficiently tested as:
+
+ ((sizetype) @0 - (sizetype) @2 + @1) > (@1 * 2)
+
+ as long as @1 * 2 doesn't overflow. B is the same with @1 replaced
+ with @1 - 1. */
+(for ior (truth_orif truth_or bit_ior)
+ (for cmp (le lt)
+ (simplify
+ (ior (cmp:cs (pointer_plus:s @0 INTEGER_CST@1) @2)
+ (cmp:cs (pointer_plus:s @2 @1) @0))
+ (if (!flag_trapv && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0)))
+ /* Convert the B form to the A form. */
+ (with { offset_int off = wi::to_offset (@1) - (cmp == LE_EXPR ? 1 : 0); }
+ /* Always fails for negative values. */
+ (if (wi::min_precision (off, UNSIGNED) * 2 <= TYPE_PRECISION (sizetype))
+ /* It doesn't matter whether we use @2 - @0 or @0 - @2, so let
+ tree_swap_operands_p pick a canonical order. */
+ (with { tree ptr1 = @0, ptr2 = @2;
+ if (tree_swap_operands_p (ptr1, ptr2))
+ std::swap (ptr1, ptr2); }
+ (gt (plus (minus (convert:sizetype { ptr1; })
+ (convert:sizetype { ptr2; }))
+ { wide_int_to_tree (sizetype, off); })
+ { wide_int_to_tree (sizetype, off * 2); }))))))))
Index: gcc/testsuite/gcc.dg/pointer-range-check-1.c
===================================================================
--- /dev/null 2018-07-09 14:52:09.234750850 +0100
+++ gcc/testsuite/gcc.dg/pointer-range-check-1.c 2018-07-23
15:58:33.480269844 +0100
@@ -0,0 +1,37 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-ipa-icf -fdump-tree-optimized" } */
+
+/* All four functions should be folded to:
+
+ ((sizetype) a - (sizetype) b + 15) < 30. */
+
+_Bool
+f1 (char *a, char *b)
+{
+ return (a + 16 <= b) || (b + 16 <= a);
+}
+
+_Bool
+f2 (char *a, char *b)
+{
+ return (a + 15 < b) || (b + 15 < a);
+}
+
+_Bool
+f3 (char *a, char *b)
+{
+ return (a + 16 <= b) || (b + 16 <= a);
+}
+
+_Bool
+f4 (char *a, char *b)
+{
+ return (a + 15 < b) || (b + 15 < a);
+}
+
+/* { dg-final { scan-tree-dump-times { = [^\n]* - [^\n]*;} 4 "optimized" } } */
+/* { dg-final { scan-tree-dump-times { = [^\n]* \+ [^\n]*;} 4 "optimized" } }
*/
+/* { dg-final { scan-tree-dump-times { = [^\n]*\ > [^\n]*;} 4 "optimized" } }
*/
+/* { dg-final { scan-tree-dump-not {=[^\n]*\ < [^\n]*;} "optimized" } } */
+/* { dg-final { scan-tree-dump-times { \+ 15} 4 "optimized" } } */
+/* { dg-final { scan-tree-dump-times { > 30} 4 "optimized" } } */
Index: gcc/testsuite/gcc.dg/pointer-range-check-2.c
===================================================================
--- /dev/null 2018-07-09 14:52:09.234750850 +0100
+++ gcc/testsuite/gcc.dg/pointer-range-check-2.c 2018-07-23
15:58:33.480269844 +0100
@@ -0,0 +1,31 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-ipa-icf -fwrapv-pointer -fdump-tree-optimized" } */
+
+_Bool
+f1 (char *a, char *b)
+{
+ return (a + 16 <= b) || (b + 16 <= a);
+}
+
+_Bool
+f2 (char *a, char *b)
+{
+ return (a + 15 < b) || (b + 15 < a);
+}
+
+_Bool
+f3 (char *a, char *b)
+{
+ return (a + 16 <= b) || (b + 16 <= a);
+}
+
+_Bool
+f4 (char *a, char *b)
+{
+ return (a + 15 < b) || (b + 15 < a);
+}
+
+/* { dg-final { scan-tree-dump-not { = [^\n]* - [^\n]*;} "optimized" } } */
+/* { dg-final { scan-tree-dump-times { = [^\n]* \+ [^\n]*;} 8 "optimized" } }
*/
+/* { dg-final { scan-tree-dump-times { \+ 15} 4 "optimized" } } */
+/* { dg-final { scan-tree-dump-times { \+ 16} 4 "optimized" } } */
