From be58bf98e98bb431ed26ca8be84586075fe8be82 Mon Sep 17 00:00:00 2001
From: Tamar Christina <tamar.christina@arm.com>
Date: Thu, 4 Aug 2022 16:37:25 +0100
Subject: [PATCH] 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.
---
gcc/match.pd | 5 +++++
gcc/testsuite/gcc.dg/subnot.c | 9 +++++++++
2 files changed, 14 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/subnot.c
diff --git a/gcc/match.pd b/gcc/match.pd
index d3d73e3f55c5..f82f94ad1fe6 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 000000000000..d621bacd27bd
--- /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" } } */
--
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