[COMMITTED] Use nonzero bits in range-ops to determine if < 0 is false.

[Aldy Hernandez via Gcc-patches]

For a signed integer, x < 0 is false if the sign bit in the nonzero
bits of X is clear.

Both CCP and ipa-cp can set the global nonzero bits in a range, which
means we can now use some of that information in evrp and subsequent
passes.  I've adjusted two tests which now fold things earlier because
of this optimization.

Tested on x86-64 Linux.

gcc/ChangeLog:

        * range-op.cc (operator_lt::fold_range): Use nonzero bits.

gcc/testsuite/ChangeLog:

        * g++.dg/ipa/pure-const-3.C: Adjust.
        * gcc.dg/pr102983.c: Adjust.
---
 gcc/range-op.cc                         | 3 +++
 gcc/testsuite/g++.dg/ipa/pure-const-3.C | 2 +-
 gcc/testsuite/gcc.dg/pr102983.c         | 2 +-
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index 0e16408027c..e184129f9af 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -803,6 +803,9 @@ operator_lt::fold_range (irange &r, tree type,
     r = range_true (type);
   else if (!wi::lt_p (op1.lower_bound (), op2.upper_bound (), sign))
     r = range_false (type);
+  // Use nonzero bits to determine if < 0 is false.
+  else if (op2.zero_p () && !wi::neg_p (op1.get_nonzero_bits (), sign))
+    r = range_false (type);
   else
     r = range_true_and_false (type);
   return true;
diff --git a/gcc/testsuite/g++.dg/ipa/pure-const-3.C 
b/gcc/testsuite/g++.dg/ipa/pure-const-3.C
index 172a36bedb5..b4a4673e86e 100644
--- a/gcc/testsuite/g++.dg/ipa/pure-const-3.C
+++ b/gcc/testsuite/g++.dg/ipa/pure-const-3.C
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fno-ipa-vrp -fdump-tree-optimized -fno-tree-ccp"  } */
+/* { dg-options "-O2 -fno-ipa-vrp -fdump-tree-optimized -fno-tree-ccp 
-fdisable-tree-evrp"  } */
 int *ptr;
 static int barvar;
 static int b(int a);
diff --git a/gcc/testsuite/gcc.dg/pr102983.c b/gcc/testsuite/gcc.dg/pr102983.c
index ef58af6def0..e1bd24b2e39 100644
--- a/gcc/testsuite/gcc.dg/pr102983.c
+++ b/gcc/testsuite/gcc.dg/pr102983.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-evrp" } */
+/* { dg-options "-O2 -fdump-tree-evrp -fno-tree-ccp" } */
 void foo(void);
 
 static int a = 1;
-- 
2.36.1