diff options
Diffstat (limited to 'gcc/ext-dce.cc')
| -rw-r--r-- | gcc/ext-dce.cc | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/gcc/ext-dce.cc b/gcc/ext-dce.cc index a034395..aa80c04 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 +765,25 @@ 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, the mode + change performed by Y would normally need to be a + TRUNCATE rather than a SUBREG. It is probably the + guarantee provided by SUBREG_PROMOTED_VAR_P that + allows the SUBREG in Y as an exception. We must + therefore preserve that guarantee and treat the + upper bits of the inner register as live + 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 (); |