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decodetree: Allow grouping of overlapping patterns

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Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2019-02-23 11:35:36 -08:00
parent eb6b87fac7
commit 0eff2df4a2
3 changed files with 207 additions and 22 deletions
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58
docs/devel/decodetree.rst
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@ -161,3 +161,61 @@ which will, in part, invoke::
and::
trans_addl_i(ctx, &arg_opi, insn)
Pattern Groups
==============
Syntax::
group := '{' ( pat_def | group )+ '}'
A *group* begins with a lone open-brace, with all subsequent lines
indented two spaces, and ending with a lone close-brace. Groups
may be nested, increasing the required indentation of the lines
within the nested group to two spaces per nesting level.
Unlike ungrouped patterns, grouped patterns are allowed to overlap.
Conflicts are resolved by selecting the patterns in order. If all
of the fixedbits for a pattern match, its translate function will
be called. If the translate function returns false, then subsequent
patterns within the group will be matched.
The following example from PA-RISC shows specialization of the *or*
instruction::
{
{
nop 000010 ----- ----- 0000 001001 0 00000
copy 000010 00000 r1:5 0000 001001 0 rt:5
}
or 000010 rt2:5 r1:5 cf:4 001001 0 rt:5
}
When the *cf* field is zero, the instruction has no side effects,
and may be specialized. When the *rt* field is zero, the output
is discarded and so the instruction has no effect. When the *rt2*
field is zero, the operation is ``reg[rt] | 0`` and so encodes
the canonical register copy operation.
The output from the generator might look like::
switch (insn & 0xfc000fe0) {
case 0x08000240:
/* 000010.. ........ ....0010 010..... */
if ((insn & 0x0000f000) == 0x00000000) {
/* 000010.. ........ 00000010 010..... */
if ((insn & 0x0000001f) == 0x00000000) {
/* 000010.. ........ 00000010 01000000 */
extract_decode_Fmt_0(&u.f_decode0, insn);
if (trans_nop(ctx, &u.f_decode0)) return true;
}
if ((insn & 0x03e00000) == 0x00000000) {
/* 00001000 000..... 00000010 010..... */
extract_decode_Fmt_1(&u.f_decode1, insn);
if (trans_copy(ctx, &u.f_decode1)) return true;
}
}
extract_decode_Fmt_2(&u.f_decode2, insn);
if (trans_or(ctx, &u.f_decode2)) return true;
return false;
}