[PATCH]Fix PR66556. Don't drop side-effect in simplify_const_relational_operation function.

[Renlin Li <renlin dot li at arm dot com>]

Hi all,

In simplify_const_relational_operation function, there are cases a const rtx
will be returned.

Three cases are considered in this function:
1, comparisons with upper and lower bounds.
2, Integer comparisons with zero.
3, comparison of ABS with zero.

It's fine to to the optimization if the operands have no side-effects.

For example, I am currently fixing a code generation bug for armv7-a 
bigendian.
It turns out that, the following rtx is simplified into a const, and the
side-effect with it is ignored.

(ltu:SI (lshiftrt:SI (subreg:SI (mem/c:HI (post_modify:SI (reg/f:SI 156)
                    (plus:SI (reg/f:SI 156)
                        (const_int 20 [0x14]))) [5 g+4 S2 A32]) 0)
        (const_int 1 [0x1]))
    (const_int -1 [0xffffffffffffffff]))

------------>>>>>>>>>>>>>>>>>>

(const_int 1 [0x1])

This particular case falls into category 1 mentioned above. -1, when 
regarded
as unsigned integer, is the largest unsigned integer. So the result is 
always
a const_true_rtx in this case. However, the first operand of the comparison
has POST_MODIFY side-effect.

In this case, the simplifications should be checked against side-effect.

x86_64 bootstrapping is Okay and arm-none-eabi regression test runs 
without any new issues.

Okay to commit and backport to branch 5?

Regards,
Renlin Li

gcc/ChangeLog:

2015-07-08  Renlin Li  <renlin.li@arm.com>

        PR rtl/66556
        * simplify-rtx.c (simplify_const_relational_operation): Add
        side_effects_p check.

gcc/testsuite/ChangeLog:

2015-07-08  Renlin Li  <renlin.li@arm.com>

        PR rtl/66556
        * gcc.c-torture/execute/pr66556.c: New.

diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index ca8310d..936a144 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -4930,7 +4930,8 @@ simplify_const_relational_operation (enum rtx_code code,
 
   /* Optimize comparisons with upper and lower bounds.  */
   if (HWI_COMPUTABLE_MODE_P (mode)
-      && CONST_INT_P (trueop1))
+      && CONST_INT_P (trueop1)
+      && !side_effects_p (trueop0))
     {
       int sign;
       unsigned HOST_WIDE_INT nonzero = nonzero_bits (trueop0, mode);
@@ -5043,7 +5044,7 @@ simplify_const_relational_operation (enum rtx_code code,
     }
 
   /* Optimize integer comparisons with zero.  */
-  if (trueop1 == const0_rtx)
+  if (trueop1 == const0_rtx && !side_effects_p (trueop0))
     {
       /* Some addresses are known to be nonzero.  We don't know
 	 their sign, but equality comparisons are known.  */
@@ -5094,7 +5095,7 @@ simplify_const_relational_operation (enum rtx_code code,
     }
 
   /* Optimize comparison of ABS with zero.  */
-  if (trueop1 == CONST0_RTX (mode)
+  if (trueop1 == CONST0_RTX (mode) && !side_effects_p (trueop0)
       && (GET_CODE (trueop0) == ABS
 	  || (GET_CODE (trueop0) == FLOAT_EXTEND
 	      && GET_CODE (XEXP (trueop0, 0)) == ABS)))
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr66556.c b/gcc/testsuite/gcc.c-torture/execute/pr66556.c
new file mode 100644
index 0000000..f7acf1c
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr66556.c
@@ -0,0 +1,52 @@
+/* { dg-do run } */
+
+extern void abort (void);
+
+struct {
+  unsigned f2;
+  unsigned f3 : 15;
+  unsigned f5 : 3;
+  short f6;
+} b = {0x7f8000, 6, 5, 0}, g = {8, 0, 5, 0};
+
+short d, l;
+int a, c, h = 8;
+volatile char e[237] = {4};
+short *f = &d;
+short i[5] = {3};
+char j;
+int *k = &c;
+
+int
+fn1 (unsigned p1) { return -p1; }
+
+void
+fn2 (char p1)
+{
+  a = p1;
+  e[0];
+}
+
+short
+fn3 ()
+{
+  *k = 4;
+  return *f;
+}
+
+int
+main ()
+{
+
+  unsigned m;
+  short *n = &i[4];
+
+  m = fn1 ((h && j) <= b.f5);
+  l = m > g.f3;
+  *n = 3;
+  fn2 (b.f2 >> 15);
+  if ((a & 0xff) != 0xff)
+    abort ();
+
+  return 0;
+}