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| author | Richard Stallman <rms@gnu.org> | 1993-07-26 22:16:16 +0000 |
|---|---|---|
| committer | Richard Stallman <rms@gnu.org> | 1993-07-26 22:16:16 +0000 |
| commit | 437b3c097dbc0157e978e2e31c672542cf72d564 (patch) | |
| tree | 5480a9655d364207cc743b920dacbd0dc0dd72de | |
| parent | fa1a4543fddd8de5f327b774e9cb71e62d66ee1d (diff) | |
| download | gcc-437b3c097dbc0157e978e2e31c672542cf72d564.zip gcc-437b3c097dbc0157e978e2e31c672542cf72d564.tar.gz gcc-437b3c097dbc0157e978e2e31c672542cf72d564.tar.bz2 | |
(simplify_shift_const): Inhibit hacks based on
num_sign_bit_copies if shift_mode differs from the mode of varop.
From-SVN: r4994
| -rw-r--r-- | gcc/combine.c | 40 |
1 files changed, 23 insertions, 17 deletions
diff --git a/gcc/combine.c b/gcc/combine.c index fa18f29..b821af2 100644 --- a/gcc/combine.c +++ b/gcc/combine.c @@ -7122,25 +7122,31 @@ simplify_shift_const (x, code, result_mode, varop, count) else if (count < 0) abort (); - /* An arithmetic right shift of a quantity known to be -1 or 0 - is a no-op. */ - if (code == ASHIFTRT - && (num_sign_bit_copies (varop, shift_mode) - == GET_MODE_BITSIZE (shift_mode))) - { - count = 0; - break; - } + /* If we have replaced VAROP with something wider + (such as, the SUBREG_REG), then this won't work; + num_sign_bit_copies will give the wrong answer in that case. */ + if (shift_mode == GET_MODE (varop)) + { + /* An arithmetic right shift of a quantity known to be -1 or 0 + is a no-op. */ + if (code == ASHIFTRT + && (num_sign_bit_copies (varop, shift_mode) + == GET_MODE_BITSIZE (shift_mode))) + { + count = 0; + break; + } - /* If we are doing an arithmetic right shift and discarding all but - the sign bit copies, this is equivalent to doing a shift by the - bitsize minus one. Convert it into that shift because it will often - allow other simplifications. */ + /* If we are doing an arithmetic right shift and discarding all but + the sign bit copies, this is equivalent to doing a shift by the + bitsize minus one. Convert it into that shift because it will often + allow other simplifications. */ - if (code == ASHIFTRT - && (count + num_sign_bit_copies (varop, shift_mode) - >= GET_MODE_BITSIZE (shift_mode))) - count = GET_MODE_BITSIZE (shift_mode) - 1; + if (code == ASHIFTRT + && (count + num_sign_bit_copies (varop, shift_mode) + >= GET_MODE_BITSIZE (shift_mode))) + count = GET_MODE_BITSIZE (shift_mode) - 1; + } /* We simplify the tests below and elsewhere by converting ASHIFTRT to LSHIFTRT if we know the sign bit is clear. |