From: Mark Mitchell <mark@markmitchell.com>
Date: Sat, 18 Jul 1998 15:21:13 +0000 (+0000)
Subject: loop.c (maybe_eliminate_biv_1): Avoid signed/unsigned comparison confusion when setti... 
X-Git-Tag: prereleases/egcs-1.1-prerelease~206
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fa68ae5b436211cbc6a4d9807bc461956798c6bb;p=thirdparty%2Fgcc.git

loop.c (maybe_eliminate_biv_1): Avoid signed/unsigned comparison confusion when setting cc0.

	* loop.c (maybe_eliminate_biv_1): Avoid signed/unsigned comparison
	confusion when setting cc0.

From-SVN: r21273
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 360fa628dbd0..ebbb1bdd39f6 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+Sat Jul 18 15:20:19 1998  Mark Mitchell  <mark@markmitchell.com>
+
+	* loop.c (maybe_eliminate_biv_1): Avoid signed/unsigned comparison
+	confusion when setting cc0.
+
 Fri Jul 17 03:26:12 1998  Rihcard Earnshaw (rearnsha@arm.com)
 
 	* tree.c (valid_machine_attribute): Only create a new type variant if
diff --git a/gcc/loop.c b/gcc/loop.c
index 0171741e22b7..7e2c4d1d220b 100644
--- a/gcc/loop.c
+++ b/gcc/loop.c
@@ -6550,7 +6550,42 @@ maybe_eliminate_biv_1 (x, insn, bl, eliminate_p, where)
 	  return 1;
 
 #ifdef HAVE_cc0
-      if (SET_DEST (x) == cc0_rtx && SET_SRC (x) == reg)
+      /* The idea here is to replace the SET of cc0 by a REG with
+	 a comparison involving related induction variables.
+	 Unfortunately, however, such a replacement does not work
+	 correctly if the REG is being used as signed and the
+	 replacement value is unsigned, or vice versa.  For
+	 example, in:
+
+	    for (int i = n; i >= 0; --i)
+	      s[i] = 3;
+
+	 `s' is an address (an unsigned quantity), while `i' is a
+	 signed quantity.  The exit test for the loop might look
+	 something like:
+
+	    (SET cc0 i)
+	    (JUMP (SET (PC) (IF_THEN_ELSE (LT (CC0) (CONST_INT 0))
+			     (LABEL_REF L) (PC))))
+
+	 If we replace the SET of cc0 with a comparison of the
+	 induction variable for `s + i' and the original value of `s',
+	 however, we should be change the comparison in the
+	 IF_THEN_ELSE to be unsigned.  Otherwise, an array the spans
+	 the boundary between "negative" and "positive" addresses will
+	 confuse us.
+
+	 There are related problems with overflow.  If an induction
+	 variable "wraps around" but the original value doest not, we
+	 can get confused when doing the comparison.
+
+	 Pointers can't wrap around, or overflow, in a conformant
+	 program.  Therefore, it's safe to do these optimizations if
+	 both the original REG and the values in the replacement are
+	 pointers.  For now, though, we just disable these
+	 optimizations.  */
+
+      if (0 && SET_DEST (x) == cc0_rtx && SET_SRC (x) == reg)
 	{
 	  /* Can replace with any giv that was reduced and
 	     that has (MULT_VAL != 0) and (ADD_VAL == 0).
diff --git a/gcc/testsuite/gcc.c-torture/execute/loop-2g.c b/gcc/testsuite/gcc.c-torture/execute/loop-2g.c
new file mode 100644
index 000000000000..8792dbf586b6
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/loop-2g.c
@@ -0,0 +1,63 @@
+#include <limits.h>
+
+#ifdef __unix__ /* ??? Is that good enough? */
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#ifndef MAP_ANON
+#ifdef MAP_ANONYMOUS
+#define MAP_ANON MAP_ANONYMOUS
+#else
+#define MAP_ANON MAP_FILE
+#endif
+#endif
+#ifndef MAP_FILE
+#define MAP_FILE 0
+#endif
+#ifndef MAP_FIXED
+#define MAP_FIXED 0
+#endif
+#endif
+
+#define MAP_START (void *)0x7fff8000
+#define MAP_LEN 0x10000
+
+#define OFFSET (MAP_LEN/2 - 2 * sizeof (char));
+
+f (int s, char *p)
+{
+  int i;
+  for (i = s; &p[i] < &p[40] && i >= 0; i++)
+    {
+      p[i] = -2;
+    }
+}
+
+main ()
+{
+#ifdef MAP_ANON
+  char *p;
+  int dev_zero;
+
+  dev_zero = open ("/dev/zero", O_RDONLY);
+  /* -1 is OK when we have MAP_ANON; else mmap will flag an error.  */
+  if (INT_MAX != 0x7fffffffL || sizeof (char *) != sizeof (int))
+    exit (0);
+  p = mmap (MAP_START, MAP_LEN, PROT_READ|PROT_WRITE,
+	    MAP_ANON|MAP_FIXED|MAP_PRIVATE, dev_zero, 0);
+  if (p != (char *)-1)
+    {
+      p += OFFSET;
+      p[39] = 0;
+      f (0, p);
+      if (p[39] != (char)-2)
+	abort ();
+      p[39] = 0;
+      f (-1, p);
+      if (p[39] != 0)
+	abort ();
+    }
+#endif
+  exit (0);
+}
diff --git a/gcc/testsuite/gcc.c-torture/execute/loop-2g.x b/gcc/testsuite/gcc.c-torture/execute/loop-2g.x
new file mode 100644
index 000000000000..e68b8fbb8d29
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/loop-2g.x
@@ -0,0 +1,9 @@
+# This doesn't work on m68k-motorola-sysv
+# It also doesn't work on m88k-motorola-sysv3
+
+global target_triplet
+if { [istarget "m68k-motorola-sysv"] || [istarget "m88k-motorola-sysv3"] } {
+      set torture_compile_xfail "$target_triplet"
+}
+
+return 0