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authorRichard Henderson <richard.henderson@linaro.org>2020-08-03 13:57:08 -0700
committerPeter Maydell <peter.maydell@linaro.org>2020-08-04 16:33:47 +0100
commitffdfca6fac7e87faf4d0815e5cbc31c4a53f7a3a (patch)
tree48219efab62a15218989a5d3c180e96de2d4970c /docs
parentd15532d91be177e7528310e0110e39f915779a99 (diff)
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docs/devel: Document decodetree no-overlap groups
When support for this feature went in, the update to the documentation was forgotten. Fixes: 067e8b0f45d6 Reported-by: Peter Maydell <peter.maydell@linaro.org> Signed-off-by: Richard Henderson <richard.henderson@linaro.org> Reviewed-by: Peter Maydell <peter.maydell@linaro.org> Message-id: 20200803205708.315829-1-richard.henderson@linaro.org Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Diffstat (limited to 'docs')
-rw-r--r--docs/devel/decodetree.rst33
1 files changed, 20 insertions, 13 deletions
diff --git a/docs/devel/decodetree.rst b/docs/devel/decodetree.rst
index ce7f523..74f66bf 100644
--- a/docs/devel/decodetree.rst
+++ b/docs/devel/decodetree.rst
@@ -173,18 +173,25 @@ 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.
+ group := overlap_group | no_overlap_group
+ overlap_group := '{' ( pat_def | group )+ '}'
+ no_overlap_group := '[' ( pat_def | group )+ ']'
+
+A *group* begins with a lone open-brace or open-bracket, with all
+subsequent lines indented two spaces, and ending with a lone
+close-brace or close-bracket. Groups may be nested, increasing the
+required indentation of the lines within the nested group to two
+spaces per nesting level.
+
+Patterns within overlap groups 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.
+
+Patterns within no-overlap groups are not allowed to overlap, just
+the same as ungrouped patterns. Thus no-overlap groups are intended
+to be nested inside overlap groups.
The following example from PA-RISC shows specialization of the *or*
instruction::
@@ -200,7 +207,7 @@ instruction::
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
+field is zero, the operation is ``reg[r1] | 0`` and so encodes
the canonical register copy operation.
The output from the generator might look like::