If we see a promoted subreg and TRULY_NOOP_TRUNCATION says the
truncation is not a noop, then all bits of the inner reg are live. We
cannot reduce the live mask to that of the mode of the subreg.
gcc/ChangeLog:
PR rtl-optimization/120050
* ext-dce.cc (ext_dce_process_uses): Break early if a SUBREG in
rhs is promoted and the truncation from the inner mode to the
outer mode is not a noop when handling SETs.
---
Bootstrapped on mips64el-linux-gnuabi64. Ok for trunk?
gcc/ext-dce.cc | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/gcc/ext-dce.cc b/gcc/ext-dce.cc
index a0343950141..3b21e68b90c 100644
--- a/gcc/ext-dce.cc
+++ b/gcc/ext-dce.cc
@@ -35,6 +35,7 @@ along with GCC; see the file COPYING3. If not see
#include "print-rtl.h"
#include "dbgcnt.h"
#include "diagnostic-core.h"
+#include "target.h"
/* These should probably move into a C++ class. */
static vec<bitmap_head> livein;
@@ -764,13 +765,20 @@ ext_dce_process_uses (rtx_insn *insn, rtx obj,
We don't want to mark those bits live unnecessarily
as that inhibits extension elimination in important
cases such as those in Coremark. So we need that
- outer code. */
+ outer code.
+
+ But if !TRULY_NOOP_TRUNCATION_MODES_P, those bits
+ may be actually alive with any promoted subreg
+ regardless of the outer code. See PR 120050. */
if (!REG_P (SUBREG_REG (y))
|| (SUBREG_PROMOTED_VAR_P (y)
&& ((GET_CODE (SET_SRC (x)) == SIGN_EXTEND
&& SUBREG_PROMOTED_SIGNED_P (y))
|| (GET_CODE (SET_SRC (x)) == ZERO_EXTEND
- && SUBREG_PROMOTED_UNSIGNED_P (y)))))
+ && SUBREG_PROMOTED_UNSIGNED_P (y))
+ || !TRULY_NOOP_TRUNCATION_MODES_P (
+ GET_MODE (y),
+ GET_MODE (SUBREG_REG (y))))))
break;
bit = subreg_lsb (y).to_constant ();
--
2.49.0
