[ARM] PR rtl-optimization/69904: Disallow copying/duplicating of load-exclusive operations

	PR rtl-optimization/69904
	* config/arm/arm.c (arm_cannot_copy_insn_p):
	Return true for load-exclusive instructions.

	* gcc.target/arm/pr69904.c: New test.

From-SVN: r233941

gcc/ChangeLog

+2016-03-03  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
+	PR rtl-optimization/69904
+	* config/arm/arm.c (arm_cannot_copy_insn_p):
+	Return true for load-exclusive instructions.
+
 2016-03-03  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/70021

gcc/config/arm/arm.c

@@ -13263,7 +13263,11 @@ tls_mentioned_p (rtx x)
     }
 }
 
-/* Must not copy any rtx that uses a pc-relative address.  */
+/* Must not copy any rtx that uses a pc-relative address.
+   Also, disallow copying of load-exclusive instructions that
+   may appear after splitting of compare-and-swap-style operations
+   so as to prevent those loops from being transformed away from their
+   canonical forms (see PR 69904).  */
 
 static bool
 arm_cannot_copy_insn_p (rtx_insn *insn)
@@ -13282,6 +13286,20 @@ arm_cannot_copy_insn_p (rtx_insn *insn)
 	      || XINT (x, 1) == UNSPEC_PIC_UNIFIED))
 	return true;
     }
+
+  rtx set = single_set (insn);
+  if (set)
+    {
+      rtx src = SET_SRC (set);
+      if (GET_CODE (src) == ZERO_EXTEND)
+	src = XEXP (src, 0);
+
+      /* Catch the load-exclusive and load-acquire operations.  */
+      if (GET_CODE (src) == UNSPEC_VOLATILE
+	  && (XINT (src, 1) == VUNSPEC_LL
+	      || XINT (src, 1) == VUNSPEC_LAX))
+	return true;
+    }
   return false;
 }
 

gcc/testsuite/ChangeLog

+2016-03-03  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
+	PR rtl-optimization/69904
+	* gcc.target/arm/pr69904.c: New test.
+
 2016-03-03  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/70021

gcc/testsuite/gcc.target/arm/pr69904.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -marm" } */
+/* { dg-require-effective-target arm_arch_v7a_ok } */
+/* { dg-add-options arm_arch_v7a } */
+
+/* Make sure that RTL optimizers don't do any unexpected transformations
+   on the compare_exchange loop.  */
+
+#include <stdatomic.h>
+
+atomic_uint foo;
+atomic_uint bar;
+int glob;
+
+int
+main (void)
+{
+  glob = atomic_compare_exchange_strong (&foo, &bar, 0);
+  return glob;
+}
+
+/* { dg-final { scan-assembler-times "dmb\tish" 2 } } */
+/* { dg-final { scan-assembler-times "ldrex\t" 1 } } */
+/* { dg-final { scan-assembler-times "strex\t" 1 } } */