diff options
Diffstat (limited to 'gcc/ext-dce.cc')
| -rw-r--r-- | gcc/ext-dce.cc | 43 |
1 files changed, 37 insertions, 6 deletions
diff --git a/gcc/ext-dce.cc b/gcc/ext-dce.cc index c94d1fc..14f163a 100644 --- a/gcc/ext-dce.cc +++ b/gcc/ext-dce.cc @@ -667,6 +667,12 @@ ext_dce_process_uses (rtx_insn *insn, rtx obj, if (modify && !skipped_dest && (dst_mask & ~src_mask) == 0) ext_dce_try_optimize_insn (insn, x); + /* Stripping the extension here just seems wrong on multiple + levels. It's source side handling, so it seems like it + belongs in the loop below. Stripping here also makes it + harder than necessary to properly handle live bit groups + for (ANY_EXTEND (SUBREG)) where the SUBREG has + SUBREG_PROMOTED state. */ dst_mask &= src_mask; src = XEXP (src, 0); code = GET_CODE (src); @@ -674,8 +680,8 @@ ext_dce_process_uses (rtx_insn *insn, rtx obj, /* Optimization is done at this point. We just want to make sure everything that should get marked as live is marked - from here onward. */ - + from here onward. Shouldn't the backpropagate step happen + before optimization? */ dst_mask = carry_backpropagate (dst_mask, code, src); /* We will handle the other operand of a binary operator @@ -688,7 +694,11 @@ ext_dce_process_uses (rtx_insn *insn, rtx obj, /* We're inside a SET and want to process the source operands making things live. Breaking from this loop will cause the iterator to work on sub-rtxs, so it is safe to break - if we see something we don't know how to handle. */ + if we see something we don't know how to handle. + + This code is just hokey as it really just handles trivial + unary and binary cases. Otherwise the loop exits and we + continue iterating on sub-rtxs, but outside the set context. */ unsigned HOST_WIDE_INT save_mask = dst_mask; for (;;) { @@ -704,10 +714,26 @@ ext_dce_process_uses (rtx_insn *insn, rtx obj, y = XEXP (y, 0); else if (SUBREG_P (y) && SUBREG_BYTE (y).is_constant ()) { - /* For anything but (subreg (reg)), break the inner loop - and process normally (conservatively). */ - if (!REG_P (SUBREG_REG (y))) + /* We really want to know the outer code here, ie do we + have (ANY_EXTEND (SUBREG ...)) as we need to know if + the extension matches the SUBREG_PROMOTED state. In + that case optimizers can turn the extension into a + simple copy. Which means that bits outside the + SUBREG's mode are actually live. + + 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. */ + 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))))) break; + + /* The SUBREG's mode determine the live width. */ bit = subreg_lsb (y).to_constant (); if (dst_mask) { @@ -785,6 +811,11 @@ ext_dce_process_uses (rtx_insn *insn, rtx obj, HOST_WIDE_INT size = GET_MODE_BITSIZE (GET_MODE (x)).to_constant (); HOST_WIDE_INT rn = 4 * REGNO (SUBREG_REG (x)); + /* If this is a promoted subreg, then more of it may be live than + is otherwise obvious. */ + if (SUBREG_PROMOTED_VAR_P (x)) + size = GET_MODE_BITSIZE (GET_MODE (SUBREG_REG (x))).to_constant (); + bitmap_set_bit (livenow, rn); if (size > 8) bitmap_set_bit (livenow, rn + 1); |