[PATCH] Fix PR middle-end/71654 (missed shortening of a compare)

[Patrick Palka]

Hi, this patch makes match.pd to shorten comparisons that involve a
sign-changing cast from a shorter unsigned type to a wider signed type.
This should be safe to do because a wider signed type can hold all the
possible values of a shorter unsigned type.

This change causes vrp23.c and vrp24.c to fail because it makes the
"n_sets > 0" tests within get trivially simplified by forwprop and so
there is nothing left to simplify by VRP.  Fixed by passing
-fno-tree-forwprop in these tests.

Bootstrapped + regtested on x86_64-pc-linux-gnu.  Does this look OK to commit?

gcc/ChangeLog:

        PR middle-end/71654
        * match.pd ((T)A CMP (T)B -> A CMP B): Allow (T)A to be a
        sign-changing cast from a shorter unsigned type to a wider
        signed type.

gcc/testsuite/ChangeLog:

        PR middle-end/71654
        * gcc.dg/c-c++-common/pr71654.c: New test.
        * gcc.dg/tree-ssa/vrp23: Add -fno-tree-forwprop to
        dg-options.
        * gcc.dg/tree-ssa/vrp24: Likewise.
---
 gcc/match.pd                          |  4 +++-
 gcc/testsuite/c-c++-common/pr71654.c  | 28 ++++++++++++++++++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/vrp23.c |  2 +-
 gcc/testsuite/gcc.dg/tree-ssa/vrp24.c |  2 +-
 4 files changed, 33 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/pr71654.c

diff --git a/gcc/match.pd b/gcc/match.pd
index ac7cfff..da87b02 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2350,7 +2350,9 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
     (if (TYPE_PRECISION (TREE_TYPE (@0)) > TYPE_PRECISION (TREE_TYPE (@00)))
      /* If possible, express the comparison in the shorter mode.  */
      (if ((cmp == EQ_EXPR || cmp == NE_EXPR
-          || TYPE_UNSIGNED (TREE_TYPE (@0)) == TYPE_UNSIGNED (TREE_TYPE (@00)))
+          || TYPE_UNSIGNED (TREE_TYPE (@0)) == TYPE_UNSIGNED (TREE_TYPE (@00))
+          || (!TYPE_UNSIGNED (TREE_TYPE (@0))
+              && TYPE_UNSIGNED (TREE_TYPE (@00))))
          && (types_match (TREE_TYPE (@10), TREE_TYPE (@00))
              || ((TYPE_PRECISION (TREE_TYPE (@00))
                   >= TYPE_PRECISION (TREE_TYPE (@10)))
diff --git a/gcc/testsuite/c-c++-common/pr71654.c 
b/gcc/testsuite/c-c++-common/pr71654.c
new file mode 100644
index 0000000..2942493
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr71654.c
@@ -0,0 +1,28 @@
+/* PR middle-end/71654  */
+/* { dg-do link }  */
+/* { dg-options "-O2" }  */
+
+unsigned char i0, i1;
+
+void foo (void);
+
+int
+main (void)
+{
+  int j = i0;
+  if (j < 4)
+    {
+      if (i0 & 4)
+        foo ();
+    }
+
+  unsigned int k = i1;
+  if (k < 8)
+    {
+      if (i1 & 8)
+        foo ();
+    }
+
+  return 0;
+}
+
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp23.c 
b/gcc/testsuite/gcc.dg/tree-ssa/vrp23.c
index b877ccc..ae68c090 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/vrp23.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp23.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1-details" } */
+/* { dg-options "-O2 -fno-tree-forwprop -fdump-tree-vrp1-details" } */
 
 void aa (void);
 void aos (void);
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp24.c 
b/gcc/testsuite/gcc.dg/tree-ssa/vrp24.c
index e740575..853ee21 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/vrp24.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp24.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1-details" } */
+/* { dg-options "-O2 -fno-tree-forwprop -fdump-tree-vrp1-details" } */
 
 
 struct rtx_def;
-- 
2.9.2.614.g990027a