This patch deletes REG_EQUAL note when a src register is replaced by a
constant in an assignment. This is to prevent spurious equivalences
between the constant and the expression in the REG_EQUAL note. In the
bug reported in PR 62146, an assignment in one branch (which is
actually dead) of an IF statement has a REG_EQUAL note equating a
register with an expression. Conditional copy propagation replaces the
register with 0. The instruction is hoisted above the branch
subsequently and then the value 0 is equated with the expression in
the REG_EQUAL. Is this ok for 4.9 branch if all tests pass?
This patch looks applicable to trunk as well, but I don't have a test
case to reproduce the issue in trunk.
ChangeLog:
2014-08-25 Easwaran Raman <era...@google.com>
PR rtl-optimization/62146
* cprop.c (try_replace_reg): Remove REG_EQUAL note when a constant is
propagated into the src of an assignment.
testsuite/ChangeLog
2014-08-25 Easwaran Raman <era...@google.com>
PR rtl-optimization/62146
* testsuite/g++.dg/opt/pr62146.C: New.
Index: gcc/testsuite/g++.dg/opt/pr62146.C
===================================================================
--- gcc/testsuite/g++.dg/opt/pr62146.C (revision 0)
+++ gcc/testsuite/g++.dg/opt/pr62146.C (revision 0)
@@ -0,0 +1,51 @@
+/* PR rtl-optimization/62146 */
+/* { dg-do compile } */
+/* { dg-options "-O2 " } */
+class F
+{
+public:
+ virtual ~ F ();
+};
+template < class CL > class G:public F
+{
+ int *member_;
+public:
+ G ( int *b): member_ (0)
+ {
+ }
+};
+
+class D
+{
+public:
+ template < class CL > void RegisterNonTagCallback (int,
+ void (CL::
+ *p3) ())
+ {
+ InternalRegisterNonTag (p3 ? new G < CL > ( 0) : 0);
+ } void InternalRegisterNonTag (F *);
+};
+
+void fn1 ();
+class C1
+{
+ void foo();
+ class TokenType
+ {
+ public:
+ void AddToken ()
+ {
+ }
+ };
+ C1::TokenType bar_t;
+};
+D a;
+void C1::foo()
+{
+ if (&bar_t)
+ fn1 ();
+ for (int i = 0; i < sizeof 0; ++i)
+ a.RegisterNonTagCallback (0, &TokenType::AddToken);
+}
+
+/* { dg-final { scan-assembler-not "mov.*_ZN2C19TokenType8AddTokenEv, .\\\(" } } */
Index: gcc/cprop.c
===================================================================
--- gcc/cprop.c (revision 214472)
+++ gcc/cprop.c (working copy)
@@ -790,8 +790,11 @@ try_replace_reg (rtx from, rtx to, rtx insn)
/* REG_EQUAL may get simplified into register.
We don't allow that. Remove that note. This code ought
not to happen, because previous code ought to synthesize
- reg-reg move, but be on the safe side. */
- if (note && REG_NOTE_KIND (note) == REG_EQUAL && REG_P (XEXP (note, 0)))
+ reg-reg move, but be on the safe side. The REG_EQUAL note is
+ also removed when the source is a constant. */
+ if (note && REG_NOTE_KIND (note) == REG_EQUAL
+ && (REG_P (XEXP (note, 0))
+ || (set && CONSTANT_P (SET_SRC (set)))))
remove_note (insn, note);
return success;
