http://gcc.gnu.org/ml/gcc-patches/2008-02/msg01094.html

	PR 33738
	* tree-vrp.c (vrp_evaluate_conditional): With
	-Wtype-limits, emit a warning when comparing against a
	constant outside the natural range of OP0's type.
	* c.opt (Wtype-limits): Move ...
	* common.opt (Wtype-limits): ... here.

testsuite/ChangeLog

	PR 33738
	* g++.dg/warn/pr33738.C: New.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@132591 138bc75d-0d04-0410-961f-82ee72b054a4

6 files changed, 90 insertions, 4 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 0d159ee770f..989cada2eed 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,14 @@
+2008-02-24  Diego Novillo  <dnovillo@google.com>
+
+	http://gcc.gnu.org/ml/gcc-patches/2008-02/msg01094.html
+
+	PR 33738
+	* tree-vrp.c (vrp_evaluate_conditional): With
+	-Wtype-limits, emit a warning when comparing against a
+	constant outside the natural range of OP0's type.
+	* c.opt (Wtype-limits): Move ...
+	* common.opt (Wtype-limits): ... here.
+
 2008-02-24  Edmar Wienskoski  <edmar@freescale.com>
 
 	* config.gcc (powerpc*-*-*): Add new cores e300c2 and e300c3.
diff --git a/gcc/c.opt b/gcc/c.opt
index 94f0398419d..72165b96660 100644
--- a/gcc/c.opt
+++ b/gcc/c.opt
@@ -123,10 +123,6 @@ Wall
 C ObjC C++ ObjC++ Warning
 Enable most warning messages
 
-Wtype-limits
-C ObjC C++ ObjC++ Var(warn_type_limits) Init(-1) Warning
-Warn if a comparison is always true or always false due to the limited range of the data type
-
 Wassign-intercept
 ObjC ObjC++ Var(warn_assign_intercept) Warning
 Warn whenever an Objective-C assignment is being intercepted by the garbage collector
diff --git a/gcc/common.opt b/gcc/common.opt
index ea48ba7d760..3a64d2a1a83 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -193,6 +193,10 @@ Wsystem-headers
 Common Var(warn_system_headers) Warning
 Do not suppress warnings from system headers
 
+Wtype-limits
+Common Var(warn_type_limits) Init(-1) Warning
+Warn if a comparison is always true or always false due to the limited range of the data type
+
 Wuninitialized
 Common Var(warn_uninitialized) Warning
 Warn about uninitialized automatic variables
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 0a0259b2dff..6fc79d4130f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2008-02-24  Diego Novillo  <dnovillo@google.com>
+
+	http://gcc.gnu.org/ml/gcc-patches/2008-02/msg01094.html
+
+	PR 33738
+	* g++.dg/warn/pr33738.C: New.
+
 2008-02-24  Richard Sandiford  <rsandifo@nildram.co.uk>
 
 	* gcc.c-torture/execute/nest-align-1.x: New file.
diff --git a/gcc/testsuite/g++.dg/warn/pr33738.C b/gcc/testsuite/g++.dg/warn/pr33738.C
new file mode 100644
index 00000000000..8847b6e342c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/pr33738.C
@@ -0,0 +1,26 @@
+// { dg-do run }
+// { dg-options "-O2 -Wtype-limits" }
+extern void link_error (void);
+
+enum Alpha {
+ ZERO = 0, ONE, TWO, THREE
+};
+
+Alpha a2;
+
+int m1 = -1;
+int GetM1() {
+ return m1;
+}
+
+int main() {
+ a2 = static_cast<Alpha>(GetM1());
+ if (a2 == -1) {	// { dg-warning "always false due" }
+    link_error ();
+ }
+ if (-1 == a2) {	// { dg-warning "always false due" }
+    link_error ();
+ }
+ return 0;
+}
+
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index f9615d1f815..eaeaea08902 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -5077,6 +5077,48 @@ vrp_evaluate_conditional (tree cond, tree stmt)
 	}
     }
 
+  if (warn_type_limits
+      && ret
+      && TREE_CODE_CLASS (TREE_CODE (cond)) == tcc_comparison)
+    {
+      /* If the comparison is being folded and the operand on the LHS
+	 is being compared against a constant value that is outside of
+	 the natural range of OP0's type, then the predicate will
+	 always fold regardless of the value of OP0.  If -Wtype-limits
+	 was specified, emit a warning.  */
+      const char *warnmsg = NULL;
+      tree op0 = TREE_OPERAND (cond, 0);
+      tree op1 = TREE_OPERAND (cond, 1);
+      tree type = TREE_TYPE (op0);
+      value_range_t *vr0 = get_value_range (op0);
+
+      if (vr0->type != VR_VARYING
+	  && INTEGRAL_TYPE_P (type)
+	  && vrp_val_is_min (vr0->min)
+	  && vrp_val_is_max (vr0->max)
+	  && is_gimple_min_invariant (op1))
+	{
+	  if (integer_zerop (ret))
+	    warnmsg = G_("comparison always false due to limited range of "
+		         "data type");
+	  else
+	    warnmsg = G_("comparison always true due to limited range of "
+			 "data type");
+	}
+
+      if (warnmsg)
+	{
+	  location_t locus;
+
+	  if (!EXPR_HAS_LOCATION (stmt))
+	    locus = input_location;
+	  else
+	    locus = EXPR_LOCATION (stmt);
+
+	  warning (OPT_Wtype_limits, "%H%s", &locus, warnmsg);
+	}
+    }
+
   return ret;
 }