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| author | Pranith Kumar <bobby.prani@gmail.com> | 2016-08-23 09:48:25 -0400 |
|---|---|---|
| committer | Richard Henderson <rth@twiddle.net> | 2016-09-16 08:12:12 -0700 |
| commit | 34f939218ce78163171addd63750e1e0300376ab (patch) | |
| tree | b753d7c12df7c6c955bc93e3947c97cd7428125b | |
| parent | cc19e497a047193db5083425957d7292c8dd3226 (diff) | |
| download | qemu-34f939218ce78163171addd63750e1e0300376ab.zip | |
tcg: Optimize fence instructions
This commit optimizes fence instructions. Two optimizations are
currently implemented: (1) unnecessary duplicate fence instructions,
and (2) merging weaker fences into a stronger fence.
[rth: Merge tcg_optimize_mb back into tcg_optimize, so that we only
loop over the opcode stream once. Merge "unrelated" weaker barriers
into one stronger barrier.]
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Message-Id: <20160823134825.32578-1-bobby.prani@gmail.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>
| -rw-r--r-- | tcg/optimize.c | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/tcg/optimize.c b/tcg/optimize.c index cffe89b525..9998ac7413 100644 --- a/tcg/optimize.c +++ b/tcg/optimize.c @@ -542,6 +542,7 @@ static bool swap_commutative2(TCGArg *p1, TCGArg *p2) void tcg_optimize(TCGContext *s) { int oi, oi_next, nb_temps, nb_globals; + TCGArg *prev_mb_args = NULL; /* Array VALS has an element for each temp. If this temp holds a constant then its value is kept in VALS' element. @@ -1295,5 +1296,43 @@ void tcg_optimize(TCGContext *s) } break; } + + /* Eliminate duplicate and redundant fence instructions. */ + if (prev_mb_args) { + switch (opc) { + case INDEX_op_mb: + /* Merge two barriers of the same type into one, + * or a weaker barrier into a stronger one, + * or two weaker barriers into a stronger one. + * mb X; mb Y => mb X|Y + * mb; strl => mb; st + * ldaq; mb => ld; mb + * ldaq; strl => ld; mb; st + * Other combinations are also merged into a strong + * barrier. This is stricter than specified but for + * the purposes of TCG is better than not optimizing. + */ + prev_mb_args[0] |= args[0]; + tcg_op_remove(s, op); + break; + + default: + /* Opcodes that end the block stop the optimization. */ + if ((def->flags & TCG_OPF_BB_END) == 0) { + break; + } + /* fallthru */ + case INDEX_op_qemu_ld_i32: + case INDEX_op_qemu_ld_i64: + case INDEX_op_qemu_st_i32: + case INDEX_op_qemu_st_i64: + case INDEX_op_call: + /* Opcodes that touch guest memory stop the optimization. */ + prev_mb_args = NULL; + break; + } + } else if (opc == INDEX_op_mb) { + prev_mb_args = args; + } } } |