match.pd: Optimize ~(~X +- Y) into (X -+ Y) [PR94921]

According to my verification proglet, this transformation for signed types
with undefined overflow doesn't introduce nor remove any UB cases, so should
be valid even for signed integral types.
Not using a for because of the :c on plus which can't be there on minus.

2020-05-06  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/94921
	* match.pd (~(~X - Y) -> X + Y, ~(~X + Y) -> X - Y): New
	simplifications.

	* gcc.dg/tree-ssa/pr94921.c: New test.

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index e0dd54cdfe7468fbfd75b9dda074804d05a1be94..8bb28935555074df43ee092f9abbb8933522402e 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2020-05-06  Jakub Jelinek  <jakub@redhat.com>
+
+       PR tree-optimization/94921
+       * match.pd (~(~X - Y) -> X + Y, ~(~X + Y) -> X - Y): New
+       simplifications.
+
 2020-05-06  Richard Biener  <rguenther@suse.de>
 
        PR tree-optimization/94965

diff --git a/gcc/match.pd b/gcc/match.pd
index d9575179655111a6112221951a9583b4919f762c..9259dd4ddaa1dec50a53146401680e4349f82d00 100644 (file)
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1010,6 +1010,14 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   @0))
 #endif
 
+/* ~(~X - Y) -> X + Y and ~(~X + Y) -> X - Y.  */
+(simplify
+ (bit_not (minus (bit_not @0) @1))
+ (plus @0 @1))
+(simplify
+ (bit_not (plus:c (bit_not @0) @1))
+ (minus @0 @1))
+
 /* x + (x & 1) -> (x + 1) & ~1 */
 (simplify
  (plus:c @0 (bit_and:s @0 integer_onep@1))

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 1f01ff0b886034da6fd582d0c5dfc19abfc0c97c..a66a01244f96c572c20149d51f67dfd28b16907c 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,9 @@
 2020-05-06  Jakub Jelinek  <jakub@redhat.com>
 
+       PR tree-optimization/94921
+       * match.pd (~(~X - Y) -> X + Y, ~(~X + Y) -> X - Y): New
+       simplifications.
+
        PR rtl-optimization/94873
        * gcc.dg/pr94873.c: New test.
 

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr94921.c b/gcc/testsuite/gcc.dg/tree-ssa/pr94921.c
new file mode 100644 (file)
index 0000000..2c752ca
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr94921.c
@@ -0,0 +1,18 @@
+/* PR tree-optimization/94921 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-final { scan-tree-dump " \[ab]_\[0-9]+\\\(D\\\) \\+ \[ab]_\[0-9]+\\\(D\\\);" "optimized" } } */
+/* { dg-final { scan-tree-dump " c_\[0-9]+\\\(D\\\) - d_\[0-9]+\\\(D\\\);" "optimized" } } */
+/* { dg-final { scan-tree-dump-not " ~\[abcd]\?_\[0-9]\+" "optimized" } } */
+
+int
+foo (int a, int b)
+{
+  return ~(~a - b);
+}
+
+int
+bar (int c, int d)
+{
+  return ~(~c + d);
+}