[gcc r13-2339] Implement ranger folder for __builtin_signbit.

[Aldy Hernandez <aldyh@gcc.gnu.org>]

https://gcc.gnu.org/g:0550e306d4b5aaf7bdb6e908d265dbaa63344271

commit r13-2339-g0550e306d4b5aaf7bdb6e908d265dbaa63344271
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Wed Aug 31 14:41:29 2022 +0200

    Implement ranger folder for __builtin_signbit.
    
    Now that we keep track of the signbit, we can use it to fold __builtin_signbit.
    
    I am assuming I don't have try too hard to get the actual signbit
    number and 1 will do.  Especially, since we're inconsistent in trunk whether
    we fold the builtin or whether we calculate it at runtime.
    
    abulafia:~$ cat a.c
    float nzero = -0.0;
    
    main(){
        printf("0x%x\n", __builtin_signbit(-0.0));
        printf("0x%x\n", __builtin_signbit(nzero));
    }
    abulafia:~$ gcc a.c -w && ./a.out
    0x1
    0x80000000
    
    It is amazing that we've been failing to fold something as simple as
    this:
    
            if (x > 5.0)
              num = __builtin_signbit (x);
    
    It does the right thing now :-P.
    
    gcc/ChangeLog:
    
            * gimple-range-fold.cc
            (fold_using_range::range_of_builtin_int_call): Add case for
            CFN_BUILT_IN_SIGNBIT.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/tree-ssa/vrp-float-signbit-1.c: New test.

Diff:
---
 gcc/gimple-range-fold.cc                            | 20 ++++++++++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-1.c | 12 ++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/gcc/gimple-range-fold.cc b/gcc/gimple-range-fold.cc
index b0b22106320..d8497fc9be7 100644
--- a/gcc/gimple-range-fold.cc
+++ b/gcc/gimple-range-fold.cc
@@ -1023,6 +1023,26 @@ fold_using_range::range_of_builtin_int_call (irange &r, gcall *call,
 	break;
       }
 
+    case CFN_BUILT_IN_SIGNBIT:
+      {
+	arg = gimple_call_arg (call, 0);
+	frange tmp;
+	if (src.get_operand (tmp, arg))
+	  {
+	    if (tmp.get_signbit ().varying_p ())
+	      return false;
+	    if (tmp.get_signbit ().yes_p ())
+	      {
+		tree one = build_one_cst (type);
+		r.set (one, one);
+	      }
+	    else
+	      r.set_zero (type);
+	    return true;
+	  }
+	break;
+      }
+
     case CFN_BUILT_IN_TOUPPER:
       {
 	arg = gimple_call_arg (call, 0);
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-1.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-1.c
new file mode 100644
index 00000000000..3fa783ec460
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-1.c
@@ -0,0 +1,12 @@
+// { dg-do compile }
+// { dg-options "-O2 -fdump-tree-evrp" }
+
+int num;
+
+void func(float x)
+{
+  if (x > 5.0)
+    num = __builtin_signbit (x);
+}
+
+// { dg-final { scan-tree-dump-times "num = 0;" 1 "evrp" } }