diff options
| author | Richard Kenner <kenner@gcc.gnu.org> | 1993-07-05 17:56:42 -0400 |
|---|---|---|
| committer | Richard Kenner <kenner@gcc.gnu.org> | 1993-07-05 17:56:42 -0400 |
| commit | bc0776c6205c3f0804cb607214ff51c7eab20a18 (patch) | |
| tree | 7bd4abba0b13ff7df97f686ded23422e7c788c34 /gcc | |
| parent | 05a0d5eabb68d036b5717738d601abac96a46c96 (diff) | |
| download | gcc-bc0776c6205c3f0804cb607214ff51c7eab20a18.zip gcc-bc0776c6205c3f0804cb607214ff51c7eab20a18.tar.gz gcc-bc0776c6205c3f0804cb607214ff51c7eab20a18.tar.bz2 | |
(subst, case PLUS): Simplify (plus (comp A B) -1), etc.
From-SVN: r4853
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/combine.c | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/gcc/combine.c b/gcc/combine.c index fb63387..b91558a 100644 --- a/gcc/combine.c +++ b/gcc/combine.c @@ -3394,7 +3394,22 @@ subst (x, from, to, in_dest, unique_copy) goto restart; } - /* If only the low-order bit of X is possible nonzero, (plus x -1) + /* (plus (comparison A B) C) can become (neg (rev-comp A B)) if + C is 1 and STORE_FLAG_VALUE is -1 or if C is -1 and STORE_FLAG_VALUE + is 1. This produces better code than the alternative immediately + below. */ + if (GET_RTX_CLASS (GET_CODE (XEXP (x, 0))) == '<' + && reversible_comparison_p (XEXP (x, 0)) + && ((STORE_FLAG_VALUE == -1 && XEXP (x, 1) == const1_rtx) + || (STORE_FLAG_VALUE == 1 && XEXP (x, 1) == constm1_rtx))) + { + x = gen_binary (reverse_condition (GET_CODE (XEXP (x, 0))), + mode, XEXP (XEXP (x, 0), 0), XEXP (XEXP (x, 0), 1)); + x = gen_unary (NEG, mode, x); + goto restart; + } + + /* If only the low-order bit of X is possibly nonzero, (plus x -1) can become (ashiftrt (ashift (xor x 1) C) C) where C is the bitsize of the mode - 1. This allows simplification of "a = (b & 8) == 0;" */ |