From: Richard Biener <rguenther@suse.de>
Date: Thu, 18 Jun 2015 14:47:18 +0000 (+0000)
Subject: backport: re PR middle-end/56917 (-ftrapv detects a overflow wrongly.)
X-Git-Tag: releases/gcc-4.8.5~56
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6b7a887d1e70bad7b5230fe55a7145a5316457d8;p=thirdparty%2Fgcc.git

backport: re PR middle-end/56917 (-ftrapv detects a overflow wrongly.)

2015-06-18  Richard Biener  <rguenther@suse.de>

	Backport from mainline
	2014-12-04  Marek Polacek  <polacek@redhat.com>

	PR middle-end/56917
	* fold-const.c (fold_unary_loc): Perform the negation in A's type
	when transforming ~ (A - 1) or ~ (A + -1) to -A.

	* g++.dg/other/const4.C: New testcase.

From-SVN: r224617
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4ee4479e2278..2bada22e200c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2015-06-18  Richard Biener  <rguenther@suse.de>
+
+	Backport from mainline
+	2014-12-04  Marek Polacek  <polacek@redhat.com>
+
+	PR middle-end/56917
+	* fold-const.c (fold_unary_loc): Perform the negation in A's type
+	when transforming ~ (A - 1) or ~ (A + -1) to -A.
+
 2015-06-18  Jakub Jelinek  <jakub@redhat.com>
 
 	PR tree-optimization/66233
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index f06bef615736..d3c2569adc35 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -8249,9 +8249,14 @@ fold_unary_loc (location_t loc, enum tree_code code, tree type, tree op0)
 		    && integer_onep (TREE_OPERAND (arg0, 1)))
 		   || (TREE_CODE (arg0) == PLUS_EXPR
 		       && integer_all_onesp (TREE_OPERAND (arg0, 1)))))
-	return fold_build1_loc (loc, NEGATE_EXPR, type,
-			    fold_convert_loc (loc, type,
-					      TREE_OPERAND (arg0, 0)));
+	{
+	  /* Perform the negation in ARG0's type and only then convert
+	     to TYPE as to avoid introducing undefined behavior.  */
+	  tree t = fold_build1_loc (loc, NEGATE_EXPR,
+				    TREE_TYPE (TREE_OPERAND (arg0, 0)),
+				    TREE_OPERAND (arg0, 0));
+	  return fold_convert_loc (loc, type, t);
+	}
       /* Convert ~(X ^ Y) to ~X ^ Y or X ^ ~Y if ~X or ~Y simplify.  */
       else if (TREE_CODE (arg0) == BIT_XOR_EXPR
 	       && (tem = fold_unary_loc (loc, BIT_NOT_EXPR, type,
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 6331bcbdaeaf..27d71ca069d0 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2015-06-18  Richard Biener  <rguenther@suse.de>
+
+	Backport from mainline
+	2014-12-04  Marek Polacek  <polacek@redhat.com>
+
+	PR middle-end/56917
+	* g++.dg/other/const4.C: New testcase.
+
 2015-06-18  Jakub Jelinek  <jakub@redhat.com>
 
 	PR tree-optimization/66233
diff --git a/gcc/testsuite/g++.dg/other/const4.C b/gcc/testsuite/g++.dg/other/const4.C
new file mode 100644
index 000000000000..6e30d9e906cb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/other/const4.C
@@ -0,0 +1,10 @@
+// { dg-do compile }
+
+int lValue;
+int main()
+{
+  switch (lValue)
+    {
+    case -(int)((2U << (8 * sizeof(int) - 2)) - 1) - 1:;
+    }
+}