This pattern shows up with some C++ code (std::vector<bool>) where we get:
```
_9 = _201 - _36;
_10 = (long unsigned int) _9;
_11 = -_10;
_12 = _201 + _11;
```
In the original code it was `end - (end - begin)` but with inlined functions so
it
is not direct fixable.
This patch adds a new amtch pattern like what was added in
r0-128019-g77574c353464b3 (and then moved to match with
r5-4705-ga499aac5dfa5d9).
Bootstrapped and tested on x86_64-linux-gnu.
PR tree-optimization/121921
gcc/ChangeLog:
* match.pd (`eptr - (eptr - bptr)`): New patterns.
gcc/testsuite/ChangeLog:
* gcc.dg/pr121921-1.c: New testcase.
Signed-off-by: Andrew Pinski <andrew.pin...@oss.qualcomm.com>
---
gcc/match.pd | 24 ++++++++++++++++++++++++
gcc/testsuite/gcc.dg/pr121921-1.c | 14 ++++++++++++++
2 files changed, 38 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/pr121921-1.c
diff --git a/gcc/match.pd b/gcc/match.pd
index dbbb7b51275..5dea74aabe2 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3047,6 +3047,30 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(if (TYPE_PRECISION (TREE_TYPE (@2)) >= TYPE_PRECISION (TREE_TYPE (@3)))
(convert @1)))
+/* Likewise but with an additional negate here
+ to swap the order of the subtraction. */
+/* Pattern match
+ tem1 = (long) ptr1;
+ tem2 = (long) ptr2;
+ tem3 = tem1 - tem2;
+ tem4 = (unsigned long) tem3;
+ tem5 = -tem3;
+ tem5 = ptr1 + tem5;
+ and produce
+ tem5 = ptr2; */
+(simplify
+ (pointer_plus @0 (negate (convert?@2 (minus@3 (convert @0) (convert @1)))))
+ /* Conditionally look through a sign-changing conversion. */
+ (if (TYPE_PRECISION (TREE_TYPE (@2)) == TYPE_PRECISION (TREE_TYPE (@3))
+ && ((GIMPLE && useless_type_conversion_p (type, TREE_TYPE (@1)))
+ || (GENERIC && type == TREE_TYPE (@1))))
+ @1))
+/* ptr0 - (ptr0 - ptr1) -> ptr1 */
+(simplify
+ (pointer_plus @0 (negate (convert?@2 (pointer_diff@3 @@0 @1))))
+ (if (TYPE_PRECISION (TREE_TYPE (@2)) >= TYPE_PRECISION (TREE_TYPE (@3)))
+ (convert @1)))
+
/* Pattern match
tem = (sizetype) ptr;
tem = tem & algn;
diff --git a/gcc/testsuite/gcc.dg/pr121921-1.c
b/gcc/testsuite/gcc.dg/pr121921-1.c
new file mode 100644
index 00000000000..b11afc819da
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr121921-1.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-cddce1" } */
+
+/* PR tree-optimization/121921 */
+
+int *
+fx (int *b, int *e)
+{
+ __SIZE_TYPE__ p = b - e;
+ /* The first forwprop pass should optimize this to return e; */
+ return b - p;
+}
+
+/* { dg-final { scan-tree-dump "return e" "cddce1" } } */
--
2.43.0
