[PR31531] MATCH: Improve ~a < ~b and ~a < CST, allow a nop cast inbetween ~ and a/b

Currently we able to simplify `~a CMP ~b` to `b CMP a` but we should allow a nop
conversion in between the `~` and the `a` which can show up. A similarly thing should
be done for `~a CMP CST`.

I had originally submitted the `~a CMP CST` case as
https://gcc.gnu.org/pipermail/gcc-patches/2021-November/585088.html;
I noticed we should do the same thing for the `~a CMP ~b` case and combined
it with that one here.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

	PR tree-optimization/31531

gcc/ChangeLog:

	* match.pd (~X op ~Y): Allow for an optional nop convert.
	(~X op C): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr31531-1.c: New test.
	* gcc.dg/tree-ssa/pr31531-2.c: New test.

3 files changed, 59 insertions, 4 deletions

diff --git a/gcc/match.pd b/gcc/match.pd
index 51e5065..e76ec1e 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -5944,18 +5944,20 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 /* Fold ~X op ~Y as Y op X.  */
 (for cmp (simple_comparison)
  (simplify
-  (cmp (bit_not@2 @0) (bit_not@3 @1))
+  (cmp (nop_convert1?@4 (bit_not@2 @0)) (nop_convert2? (bit_not@3 @1)))
   (if (single_use (@2) && single_use (@3))
-   (cmp @1 @0))))
+   (with { tree otype = TREE_TYPE (@4); }
+    (cmp (convert:otype @1) (convert:otype @0))))))
 
 /* Fold ~X op C as X op' ~C, where op' is the swapped comparison.  */
 (for cmp (simple_comparison)
      scmp (swapped_simple_comparison)
  (simplify
-  (cmp (bit_not@2 @0) CONSTANT_CLASS_P@1)
+  (cmp (nop_convert? (bit_not@2 @0)) CONSTANT_CLASS_P@1)
   (if (single_use (@2)
        && (TREE_CODE (@1) == INTEGER_CST || TREE_CODE (@1) == VECTOR_CST))
-   (scmp @0 (bit_not @1)))))
+   (with { tree otype = TREE_TYPE (@1); }
+    (scmp (convert:otype @0) (bit_not @1))))))
 
 (for cmp (simple_comparison)
  (simplify
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr31531-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr31531-1.c
new file mode 100644
index 0000000..c272991
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr31531-1.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* PR tree-optimization/31531 */
+
+int f(int a)
+{
+  int b = ~a;
+  return b<0;
+}
+
+
+int f1(unsigned a)
+{
+  int b = ~a;
+  return b<0;
+}
+/* We should convert the above two functions from b <0 to ((int)a) >= 0. */
+/* { dg-final { scan-tree-dump-times ">= 0" 2 "optimized"} } */
+/* { dg-final { scan-tree-dump-times "~" 0 "optimized"} } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr31531-2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr31531-2.c
new file mode 100644
index 0000000..865ea29
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr31531-2.c
@@ -0,0 +1,34 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* PR tree-optimization/31531 */
+
+int f0(unsigned x, unsigned t)
+{
+        x = ~x;
+        t = ~t;
+        int xx = x;
+        int tt = t;
+        return tt < xx;
+}
+
+int f1(unsigned x, int t)
+{
+        x = ~x;
+        t = ~t;
+        int xx = x;
+        int tt = t;
+        return tt < xx;
+}
+
+int f2(int x, unsigned t)
+{
+        x = ~x;
+        t = ~t;
+        int xx = x;
+        int tt = t;
+        return tt < xx;
+}
+
+
+/* We should be able to remove all ~ from the above functions. */
+/* { dg-final { scan-tree-dump-times "~" 0 "optimized"} } */