From: Aldy Hernandez <aldyh@redhat.com>
Date: Fri, 1 Oct 2021 11:05:36 +0000 (+0200)
Subject: [PR102546] X << Y being non-zero implies X is also non-zero.
X-Git-Tag: basepoints/gcc-13~4225
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=5f9ccf17de7f7581412c6bffd4a37beca9a79836;p=thirdparty%2Fgcc.git

[PR102546] X << Y being non-zero implies X is also non-zero.

This patch teaches this to range-ops.

Tested on x86-64 Linux.

gcc/ChangeLog:

	PR tree-optimization/102546
	* range-op.cc (operator_lshift::op1_range): Teach range-ops that
	X << Y is non-zero implies X is also non-zero.
---

diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index 5e37133026d7..2baca4a197f3 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -2078,6 +2078,12 @@ operator_lshift::op1_range (irange &r,
 			    relation_kind rel ATTRIBUTE_UNUSED) const
 {
   tree shift_amount;
+
+  if (!lhs.contains_p (build_zero_cst (type)))
+    r.set_nonzero (type);
+  else
+    r.set_varying (type);
+
   if (op2.singleton_p (&shift_amount))
     {
       wide_int shift = wi::to_wide (shift_amount);
@@ -2089,21 +2095,24 @@ operator_lshift::op1_range (irange &r,
 	return false;
       if (shift == 0)
 	{
-	  r = lhs;
+	  r.intersect (lhs);
 	  return true;
 	}
 
       // Work completely in unsigned mode to start.
       tree utype = type;
+      int_range_max tmp_range;
       if (TYPE_SIGN (type) == SIGNED)
 	{
 	  int_range_max tmp = lhs;
 	  utype = unsigned_type_for (type);
 	  range_cast (tmp, utype);
-	  op_rshift.fold_range (r, utype, tmp, op2);
+	  op_rshift.fold_range (tmp_range, utype, tmp, op2);
 	}
       else
-	op_rshift.fold_range (r, utype, lhs, op2);
+	op_rshift.fold_range (tmp_range, utype, lhs, op2);
+
+      r.intersect (tmp_range);
 
       // Start with ranges which can produce the LHS by right shifting the
       // result by the shift amount.
@@ -2128,7 +2137,8 @@ operator_lshift::op1_range (irange &r,
 	range_cast (r, type);
       return true;
     }
-  return false;
+
+  return !r.varying_p ();
 }
 
 bool
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr102546.c b/gcc/testsuite/gcc.dg/tree-ssa/pr102546.c
new file mode 100644
index 000000000000..4bd98747732f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr102546.c
@@ -0,0 +1,23 @@
+// { dg-do compile }
+// { dg-options "-O3 -fdump-tree-optimized" }
+
+static int a;
+static char b, c, d;
+void bar(void);
+void foo(void);
+
+int main() {
+    int f = 0;
+    for (; f <= 5; f++) {
+        bar();
+        b = b && f;
+        d = f << f;
+        if (!(a >= d || f))
+            foo();
+        c = 1;
+        for (; c; c = 0)
+            ;
+    }
+}
+
+// { dg-final { scan-tree-dump-not "foo" "optimized" } }