emit-rtl.c (set_unique_reg_note): Discard notes with side effects.

gcc/
	* emit-rtl.c (set_unique_reg_note): Discard notes with side effects.

From-SVN: r214609

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4f4c2f8..2666b24 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2014-08-27  Richard Sandiford  <rdsandiford@googlemail.com>
+
+       * emit-rtl.c (set_unique_reg_note): Discard notes with side effects.
+
 2014-08-27  David Malcolm  <dmalcolm@redhat.com>
 
        * rtl.h (JUMP_LABEL_AS_INSN): New.

diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index 6cfaef6..9abe56e 100644 (file)
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -5181,6 +5181,14 @@ set_unique_reg_note (rtx insn, enum reg_note kind, rtx datum)
         It serves no useful purpose and breaks eliminate_regs.  */
       if (GET_CODE (datum) == ASM_OPERANDS)
        return NULL_RTX;
+
+      /* Notes with side effects are dangerous.  Even if the side-effect
+        initially mirrors one in PATTERN (INSN), later optimizations
+        might alter the way that the final register value is calculated
+        and so move or alter the side-effect in some way.  The note would
+        then no longer be a valid substitution for SET_SRC.  */
+      if (side_effects_p (datum))
+       return NULL_RTX;
       break;
 
     default: