re PR rtl-optimization/67443 (DSE removes required store instruction)

2015-10-26  Richard Biener  <rguenther@suse.de>
	Dominik Vogt  <vogt@linux.vnet.ibm.com>

	PR middle-end/67443
	* alias.c (ao_ref_from_mem): Remove promoted subreg handling.
	Properly prune ref->ref for accesses outside of ref.

	* gcc.target/s390/pr67443.c: New testcase.

Co-Authored-By: Dominik Vogt <vogt@linux.vnet.ibm.com>

From-SVN: r229372

gcc/ChangeLog

+2015-10-26  Richard Biener  <rguenther@suse.de>
+	Dominik Vogt  <vogt@linux.vnet.ibm.com>
+
+	PR middle-end/67443
+	* alias.c (ao_ref_from_mem): Remove promoted subreg handling.
+	Properly prune ref->ref for accesses outside of ref.
+
 2015-10-26  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* gimple-fold.c (replace_stmt_with_simplification): Don't allow

gcc/alias.c

@@ -339,15 +339,16 @@ ao_ref_from_mem (ao_ref *ref, const_rtx mem)
       || !MEM_SIZE_KNOWN_P (mem))
     return true;
 
-  /* If the base decl is a parameter we can have negative MEM_OFFSET in
-     case of promoted subregs on bigendian targets.  Trust the MEM_EXPR
-     here.  */
+  /* If MEM_OFFSET/MEM_SIZE get us outside of ref->offset/ref->max_size
+     drop ref->ref.  */
   if (MEM_OFFSET (mem) < 0
-      && (MEM_SIZE (mem) + MEM_OFFSET (mem)) * BITS_PER_UNIT == ref->size)
-    return true;
+      || (ref->max_size != -1
+	  && ((MEM_OFFSET (mem) + MEM_SIZE (mem)) * BITS_PER_UNIT
+	      > ref->max_size)))
+    ref->ref = NULL_TREE;
 
-  /* Otherwise continue and refine size and offset we got from analyzing
-     MEM_EXPR by using MEM_SIZE and MEM_OFFSET.  */
+  /* Refine size and offset we got from analyzing MEM_EXPR by using
+     MEM_SIZE and MEM_OFFSET.  */
 
   ref->offset += MEM_OFFSET (mem) * BITS_PER_UNIT;
   ref->size = MEM_SIZE (mem) * BITS_PER_UNIT;

gcc/testsuite/ChangeLog

+2015-10-26  Richard Biener  <rguenther@suse.de>
+	Dominik Vogt  <vogt@linux.vnet.ibm.com>
+
+	PR middle-end/67443
+	* gcc.target/s390/pr67443.c: New testcase.
+
 2015-10-26  Christophe Lyon  <christophe.lyon@linaro.org>
 
 	* gfortran.dg/chmod_1.f90: Add suffix to the temporary filename to

gcc/testsuite/gcc.target/s390/pr67443.c

+/* Test case for PR/67443.  */
+
+/* { dg-do run { target s390*-*-* } } */
+/* { dg-prune-output "call-clobbered register used for global register variable" } */
+/* { dg-options "-march=z900 -fPIC -fomit-frame-pointer -O3" } */
+
+#include <assert.h>
+
+/* Block all registers except the first three argument registers.  */
+register long r0 asm ("r0");
+register long r1 asm ("r1");
+register long r5 asm ("r5");
+register long r6 asm ("r6");
+register long r7 asm ("r7");
+register long r8 asm ("r8");
+register long r9 asm ("r9");
+register long r10 asm ("r10");
+register long r11 asm ("r11");
+
+struct s_t
+{
+  unsigned f1 : 8;
+  unsigned f2 : 24;
+};
+
+__attribute__ ((noinline))
+void foo (struct s_t *ps, int c, int i)
+{
+  /* Uses r2 as address register.  */
+  ps->f1 = c;
+  /* The calculation of the value is so expensive that it's cheaper to spill ps
+     to the stack and reload it later (into a different register).
+     ==> Uses r4 as address register.*/
+  ps->f2 = i + i % 3;
+  /* If dead store elimination fails to detect that the address in r2 during
+     the first assignment is an alias of the address in r4 during the second
+     assignment, it eliminates the first assignment and the f1 field is not
+     written (bug).  */
+}
+
+int main (void)
+{
+  struct s_t s = { 0x01u, 0x020304u };
+
+  foo (&s, 0, 0);
+  assert (s.f1 == 0&& s.f2 == 0);
+
+  return 0;
+}