[gcc r13-1964] middle-end: Simplify subtract where both arguments are being bitwise inverted.

[gcc r13-1964] middle-end: Simplify subtract where both arguments are being bitwise inverted.

[Tamar Christina]

https://gcc.gnu.org/g:be58bf98e98bb431ed26ca8be84586075fe8be82

commit r13-1964-gbe58bf98e98bb431ed26ca8be84586075fe8be82
Author: Tamar Christina <tamar.christina@arm.com>
Date:   Thu Aug 4 16:37:25 2022 +0100

    middle-end: Simplify subtract where both arguments are being bitwise inverted.
    
    This adds a match.pd rule that drops the bitwwise nots when both arguments to a
    subtract is inverted. i.e. for:
    
    float g(float a, float b)
    {
      return ~(int)a - ~(int)b;
    }
    
    we instead generate
    
    float g(float a, float b)
    {
      return (int)b - (int)a;
    }
    
    We already do a limited version of this from the fold_binary fold functions but
    this makes a more general version in match.pd that applies more often.
    
    gcc/ChangeLog:
    
            * match.pd: New bit_not rule.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/subnot.c: New test.

Diff:
---
 gcc/match.pd                  | 5 +++++
 gcc/testsuite/gcc.dg/subnot.c | 9 +++++++++
 2 files changed, 14 insertions(+)

diff --git a/gcc/match.pd b/gcc/match.pd
index d3d73e3f55c..f82f94ad1fe 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1308,6 +1308,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 (simplify
  (bit_not (plus:c (bit_not @0) @1))
  (minus @0 @1))
+/* (~X - ~Y) -> Y - X.  */
+(simplify
+ (minus (bit_not @0) (bit_not @1))
+  (with { tree utype = unsigned_type_for (type); }
+   (convert (minus (convert:utype @1) (convert:utype @0)))))
 
 /* ~(X - Y) -> ~X + Y.  */
 (simplify
diff --git a/gcc/testsuite/gcc.dg/subnot.c b/gcc/testsuite/gcc.dg/subnot.c
new file mode 100644
index 00000000000..d621bacd27b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/subnot.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-optimized" } */
+
+float g(float a, float b)
+{
+  return ~(int)a - ~(int)b;
+}
+
+/* { dg-final { scan-tree-dump-not "~" "optimized" } } */