From: Eric Botcazou <ebotcazou@adacore.com>
Date: Tue, 7 Feb 2012 17:21:36 +0000 (+0000)
Subject: re PR middle-end/51994 (git-1.7.8.3 miscompiled due to negative bitpos from get_inner... 
X-Git-Tag: releases/gcc-4.7.0~533
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=f22cfd73cd9eece5e426ddfe745f998ffc665945;p=thirdparty%2Fgcc.git

re PR middle-end/51994 (git-1.7.8.3 miscompiled due to negative bitpos from get_inner_reference)

	PR middle-end/51994
	* expr.c (get_inner_reference): If there is an offset, add a negative
	bit position to it (if any).

From-SVN: r183974
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a05e801a8e4f..3d6fe256e934 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2012-02-07  Eric Botcazou  <ebotcazou@adacore.com>
+
+	PR middle-end/51994
+	* expr.c (get_inner_reference): If there is an offset, add a negative
+	bit position to it (if any).
+
 2012-02-07  Jakub Jelinek  <jakub@redhat.com>
 
 	PR rtl-optimization/52060
diff --git a/gcc/expr.c b/gcc/expr.c
index fcf177b956a0..e63ed3b71f5c 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -6716,6 +6716,24 @@ get_inner_reference (tree exp, HOST_WIDE_INT *pbitsize,
   /* Otherwise, split it up.  */
   if (offset)
     {
+      /* Avoid returning a negative bitpos as this may wreak havoc later.  */
+      if (double_int_negative_p (bit_offset))
+        {
+	  double_int mask
+	    = double_int_mask (BITS_PER_UNIT == 8
+			       ? 3 : exact_log2 (BITS_PER_UNIT));
+	  double_int tem = double_int_and_not (bit_offset, mask);
+	  /* TEM is the bitpos rounded to BITS_PER_UNIT towards -Inf.
+	     Subtract it to BIT_OFFSET and add it (scaled) to OFFSET.  */
+	  bit_offset = double_int_sub (bit_offset, tem);
+	  tem = double_int_rshift (tem,
+				   BITS_PER_UNIT == 8
+				   ? 3 : exact_log2 (BITS_PER_UNIT),
+				   HOST_BITS_PER_DOUBLE_INT, true);
+	  offset = size_binop (PLUS_EXPR, offset,
+			       double_int_to_tree (sizetype, tem));
+	}
+
       *pbitpos = double_int_to_shwi (bit_offset);
       *poffset = offset;
     }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 1f63642c0166..a433613b0c73 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2012-02-07  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* gcc.c-torture/execute/20120207-1.c: New test.
+
 2012-02-07  Jakub Jelinek  <jakub@redhat.com>
 
 	PR rtl-optimization/52060
diff --git a/gcc/testsuite/gcc.c-torture/execute/20120207-1.c b/gcc/testsuite/gcc.c-torture/execute/20120207-1.c
new file mode 100644
index 000000000000..c4716aecad80
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/20120207-1.c
@@ -0,0 +1,27 @@
+/* PR middle-end/51994 */
+/* Testcase by Uros Bizjak <ubizjak@gmail.com> */
+
+extern char *strcpy (char *, const char *);
+extern void abort (void);
+
+char __attribute__((noinline))
+test (int a)
+{
+  char buf[16];
+  char *output = buf;
+
+  strcpy (&buf[0], "0123456789");
+
+  output += a;
+  output -= 1;
+
+  return output[0];
+}
+
+int main ()
+{
+  if (test (2) != '1')
+    abort ();
+
+  return 0;
+}