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| author | Jim Wilson <wilson@cygnus.com> | 2000-05-11 04:38:29 +0000 |
|---|---|---|
| committer | Jim Wilson <wilson@gcc.gnu.org> | 2000-05-10 21:38:29 -0700 |
| commit | d2ba6dcff5dc590c7cc7f230d2826fde0c005d79 (patch) | |
| tree | 34d32bf44c63f2514522542dc6962b351ebe6453 | |
| parent | 991a40fcc2d1fa2f20584eb5a98bf949fb87bd60 (diff) | |
| download | gcc-d2ba6dcff5dc590c7cc7f230d2826fde0c005d79.zip gcc-d2ba6dcff5dc590c7cc7f230d2826fde0c005d79.tar.gz gcc-d2ba6dcff5dc590c7cc7f230d2826fde0c005d79.tar.bz2 | |
Add performance related explanatory comment.
* config/ia64/ia64.md (insv): Add comment.
From-SVN: r33836
| -rw-r--r-- | gcc/ChangeLog | 4 | ||||
| -rw-r--r-- | gcc/config/ia64/ia64.md | 15 |
2 files changed, 19 insertions, 0 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index f133e5f..a17ca24 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,7 @@ +Wed May 10 21:31:44 2000 Jim Wilson <wilson@cygnus.com> + + * config/ia64/ia64.md (insv): Add comment. + 2000-05-10 Richard Henderson <rth@cygnus.com> * Makefile.in (libgcc.a, stmp-multilib): Depend on FPBIT and DPBIT. diff --git a/gcc/config/ia64/ia64.md b/gcc/config/ia64/ia64.md index 7ccf89d..4a55b03 100644 --- a/gcc/config/ia64/ia64.md +++ b/gcc/config/ia64/ia64.md @@ -684,6 +684,21 @@ DONE; } + /* We could handle remaining cases by emitting multiple dep + instructions. + + If we need more than two dep instructions then we lose. A 6 + insn sequence mov mask1,mov mask2,shl;;and,and;;or is better than + mov;;dep,shr;;dep,shr;;dep. The former can be executed in 3 cycles, + the latter is 6 cycles on an Itanium (TM) processor, because there is + only one function unit that can execute dep and shr immed. + + If we only need two dep instruction, then we still lose. + mov;;dep,shr;;dep is still 4 cycles. Even if we optimize away + the unnecessary mov, this is still undesirable because it will be + hard to optimize, and it creates unnecessary pressure on the I0 + function unit. */ + FAIL; #if 0 |