On 2/4/21 1:48 AM, Richard Biener wrote:
On Wed, Feb 3, 2021 at 6:12 PM Martin Sebor <mse...@gmail.com> wrote:
On 2/3/21 5:01 AM, Richard Biener wrote:
On Mon, Feb 1, 2021 at 5:20 PM Martin Sebor <mse...@gmail.com> wrote:
I have pushed the tree.h comments in g:6a2053773b8. I will wait
for an approval of the changes to the manual.
Sorry for not looking earlier.
Sorry, I thought you were fine with the text after your first review.
I'll adjust the tree.h comments when we're done, though I'd like to
think the example in the manual will do a lot more to help make it
clear than the comments in tree.h can.
+/* The scope enclosing the scope NODE, or FUNCTION_DECL for the "outermost"
+ function scope. Inlined functions are chained by this so that given
+ expression E and its TREE_BLOCK(E) B, BLOCK_SUPERCONTEXT(B) is the scope
+ in which E has been made or into which E has been inlined. */
I can't really understand what you are trying to say with the second
sentence. There's
nothing really special about BLOCK_SUPERCONTEXT and inlines so I believe this
sentence only adds confusion.
The sentence explains how SUPERCONTEXT chains inlined blocks. In
the manual diff I show an example:
void f0 (char *p, int n) { memset (p, 1, n); }
void f1 (char *p, int n) { f0 (p + 1, n + 1); }
void f2 (char *p, int n) { f1 (p + 1, n + 1); }
int a[6];
void f3 (char *p, int n) { f2 (a, 3); }
The blocks for all calls inlined into f3 are chained like so:
CALL_EXPR: memset E
BLOCK #13 <--+ TREE_BLOCK (E)
+-- SUPERCONTEXT: BLOCK #12 |
| ABSTRACT_ORIGIN: BLOCK #0 --+
| | |
+-> BLOCK #12 (f1) <--|-+ |
+-- SUPERCONTEXT: BLOCK #10 | | |
| SUBBLOCKS: BLOCK #13 --|-| |
| ABSTRACT_ORIGIN: f0 ---+ | |
| | |
+-> BLOCK #10 (f2) <-+ | |
+--- SUPERCONTEXT: BLOCK #8 | | |
| SUBBLOCKS: BLOCK #12 ---|-| |
| ABSTRACT_ORIGIN: f1 ------+ |
| | |
+-> BLOCK #8 (f3) | |
+---- SUPERCONTEXT: BLOCK #0 | |
| SUBBLOCKS: BLOCK #10 --| |
| ABSTRACT_ORIGIN: f2 ---+ |
| |
+-> BLOCK #0 (f3) <---------------+
SUPERCONTEXT: f3
SUBBLOCKS: BLOCK #8
Does the following sound better? (Dropping the "in which E has been
made.")
Inlined functions are chained by this so that given expression E
and its TREE_BLOCK(E) B, BLOCK_SUPERCONTEXT(B) is the scope into
which E has been inlined.
Oh, I see what you mean. But this is misleading for the case where f0
has any blocks:
f0 (..) { { int tem; { memset (..); } } if () { }... }
because BLOCK_SUPERCONTEXT is simply the parent scope ( { int tem; ... } ) and
not yet the artifical scope we generate to wrap f0.
I haven't seen those scopes in my (admittedly simplistic) tests and
based on the internals manual have been assuming most lexical scopes
are removed during gimplification:
Additionally, all the control structures used in GENERIC are lowered
into conditional jumps, lexical scopes are removed and exception
regions are converted into an on the side exception region tree.
Is the above wrong or inaccurate? Do all nested scope not get removed?
To figure the
scope a block was
inlined to you'd have to do sth like
b = TREE_BLOCK (E);
gcc_assert (BLOCK_ABSTRACT_ORIGIN (b)); // it was inlined
while (!inlined_function_outer_scope_p (b))
b = BLOCK_SUPERCONTEXT (b);
now BLOCK_SUPERCONTEXT (b) is the block the function containing E was
inlined to.
So again, I think tree.h is not the place to document this. There
BLOCK_SUPERCONTEXT
should simply say it's pointing to the parent BLOCK.
I can simplify the text but want to make it clear it doesn't
necessarily point to a BLOCK but can also point to a FUNCTION_DECL.
So how about:
BLOCK_SUPERCONTEXT
Either a BLOCK of the enclosing scope or FUNCTION_DECL for
the "outermost" function scope. In the middle end used to chain
scopes of functions inlined into their callers. */
In the texi documentation I'd separate out the representation of
inlines and clones,
eventually put it on the BLOCK_ABSTRACT_ORIGIN documentation.
[I did not review the texi part yet - I mainly want to avoid people
being even more
confused about the tree.h comments]
I take your point that sometimes less is more. But from my personal
experience with these macros, I'd be surprised if the text that's
there now could be worse than having no comments at all.
#define BLOCK_SUPERCONTEXT(NODE) (BLOCK_CHECK (NODE)->block.supercontext)
+/* Points to the next scope at the same level of nesting as scope NODE. */
#define BLOCK_CHAIN(NODE) (BLOCK_CHECK (NODE)->block.chain)
+/* A BLOCK, or FUNCTION_DECL of the function from which a block has been
+ inlined.
... from which a block has been ultimatively copied for example by inlining.
[clones also will have abstract origins]
Okay, how's this:
/* A BLOCK, or FUNCTION_DECL of the function from which a block has been
copied by inlining or cloning. */
#define BLOCK_ABSTRACT_ORIGIN(NODE) (BLOCK_CHECK
(NODE)->block.abstract_origin)
In a scope immediately enclosing an inlined leaf expression,
+ points to the outermost scope into which it has been inlined (thus
+ bypassing all intermediate BLOCK_SUPERCONTEXTs). */
?
This describes the long arrow on the right, pointing Block #13's
ABSTRACT_ORIGIN down to Block #0. All the other AO's point down
to the next/enclosing block (arrows on the left). I didn't expect
this when I first worked with the blocks so it seemed like
an important detail to mention.
Maybe: An inlined function is represented by a scope with
BLOCK_ABSTRACT_ORIGIN being the FUNCTION_DECL of the inlined function
containing the inlined functions scope tree as children. All abstract origins
are ultimate, that is BLOCK_ABSTRACT_ORIGIN(NODE)
== BLOCK_ABSTRACT_ORIGIN(BLOCK_ABSTRACT_ORIGIN (NODE)).
The first sentence sounds good to me as far as it goes but it
doesn't capture the long arrow above. (By children I assume you
mean SUBBLOCKS, correct?)
I don't follow what you're trying to say in the second sentence.
The equality isn't true for Block #0 whose AO is null. It also
isn't true for Block #12 and the others whose AO is a DECL, not
a block.
What do you mean by "ultimate" in plain English?
Ultimate in the sense dwarf2out uses it. DWARF wants to refer to
the abstract copy. Originally (I think till GCC 9) BLOCK_ABSTRACT_ORIGIN
of a function inlined that had functions inlined into it pointed to the
inlined block of the inner inline but now it points to the original
outline copy BLOCK of the inner inline (uh, can you parse that?).
That simplifies things and is all we need.
I *think* I understand what you're saying about how it's set up now,
but I had to refer to the diagram above to help. You're referring
to the arrow below, f2's AO pointing to f1's block (and
the corresponding arrow from f3's AO to f2's block:
BLOCK #12 (f1) <----+
SUPERCONTEXT: BLOCK #10 |
SUBBLOCKS: BLOCK #13 |
ABSTRACT_ORIGIN: f0 |
|
BLOCK #10 (f2) |
SUPERCONTEXT: BLOCK #8 |
SUBBLOCKS: BLOCK #12 |
ABSTRACT_ORIGIN: f1 -----+
FWIW, a relationship between two interior parts of a larger whole
is not something I would understand by the word ultimate. A couple
of synonyms for "ultimate" are "last" and "final" and f1 is neither.
I would call f3 the ultimate origin the three inlined calls, and
that matches AO only in Block #13, but not in any others.
FWIW, if I were to try to explain it using the example I'd say
only Block #13's AO is "ultimate:" it points down in the diagram
to the block of the function into which the expression has
ultimately been inlined. The AO's of all the other intervening
inlined blocks are the DECLs of the inlined callees (up-pointing
arrows); they don't look ultimate to me in this sense.
But however this is phrased I suspect it won't be perfectly clear
without an example or a picture.
Which means giving partial info in tree.h isn't useful but confusing.
I don't think that's true. Most comments in tree.h are only partial
and don't fully describe every fine detail of whatever they document.
They may not be enough for using the thing they describe properly
and safely in every instance but they're often good enough to read
the code and what what it does. BLOCK_ABSTRACT_ORIGIN or
BLOC_SUPERCONTEXT without any comment at all isn't good enough
for even that.
Anyway, thanks for continuing to help with this. Attached are
the tweaks to tree.h. I'll post an update to the manual separately.
Martin
Richard.
Martin
#define BLOCK_ABSTRACT_ORIGIN(NODE) (BLOCK_CHECK
(NODE)->block.abstract_origin)
On 1/27/21 5:54 PM, Martin Sebor wrote:
Attached is an updated patch for both tree.h and the internals manual
documenting the most important BLOCK_ macros and what they represent.
On 1/21/21 2:52 PM, Martin Sebor wrote:
On 1/18/21 6:25 AM, Richard Biener wrote:
PS Here are my notes on the macros and the two related functions:
BLOCK: Denotes a lexical scope. Contains BLOCK_VARS of variables
declared in it, BLOCK_SUBBLOCKS of scopes nested in it, and
BLOCK_CHAIN pointing to the next BLOCK. Its BLOCK_SUPERCONTEXT
point to the BLOCK of the enclosing scope. May have
a BLOCK_ABSTRACT_ORIGIN and a BLOCK_SOURCE_LOCATION.
BLOCK_SUPERCONTEXT: The scope of the enclosing block, or FUNCTION_DECL
for the "outermost" function scope. Inlined functions are chained by
this so that given expression E and its TREE_BLOCK(E) B,
BLOCK_SUPERCONTEXT(B) is the scope (BLOCK) in which E has been made
or into which E has been inlined. In the latter case,
BLOCK_ORIGIN(B) evaluates either to the enclosing BLOCK or to
the enclosing function DECL. It's never null.
BLOCK_ABSTRACT_ORIGIN(B) is the FUNCTION_DECL of the function into
which it has been inlined, or null if B is not inlined.
It's the BLOCK or FUNCTION it was inlined _from_, not were it was
inlined to.
It's the "ultimate" source, thus the abstract copy of the block or
function decl
(for the outermost scope, aka inlined_function_outer_scope_p). It
corresponds
to what you'd expect for the DWARF abstract origin.
Thanks for the correction! It's just the "innermost" block that
points to the "ultimate" destination into which it's been inlined.
BLOCK_ABSTRACT_ORIGIN can be NULL (in case it isn't an inline instance).
BLOCK_ABSTRACT_ORIGIN: A BLOCK, or FUNCTION_DECL of the function
into which a block has been inlined. In a BLOCK immediately enclosing
an inlined leaf expression points to the outermost BLOCK into which it
has been inlined (thus bypassing all intermediate BLOCK_SUPERCONTEXTs).
BLOCK_FRAGMENT_ORIGIN: ???
BLOCK_FRAGMENT_CHAIN: ???
that's for scope blocks split by hot/cold partitioning and only
temporarily
populated.
Thanks, I now see these documented in detail in tree.h.
bool inlined_function_outer_scope_p(BLOCK) [tree.h]
Returns true if a BLOCK has a source location.
True for all but the innermost (no SUBBLOCKs?) and outermost blocks
into which an expression has been inlined. (Is this always true?)
tree block_ultimate_origin(BLOCK) [tree.c]
Returns BLOCK_ABSTRACT_ORIGIN(BLOCK), AO, after asserting that
(DECL_P(AO) && DECL_ORIGIN(AO) == AO) || BLOCK_ORIGIN(AO) == AO).
The attached diff adds the comments above to tree.h.
I looked for a good place in the manual to add the same text but I'm
not sure. Would the Blocks @subsection in generic.texi be appropriate?
Martin
diff --git a/gcc/tree.h b/gcc/tree.h
index 4f33868e8e1..86f142be6f3 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -1922,17 +1922,14 @@ class auto_suppress_location_wrappers
#define BLOCK_NONLOCALIZED_VAR(NODE,N) (*BLOCK_NONLOCALIZED_VARS (NODE))[N]
/* A chain of BLOCKs (scopes) nested within the scope NODE. */
#define BLOCK_SUBBLOCKS(NODE) (BLOCK_CHECK (NODE)->block.subblocks)
-/* The scope enclosing the scope NODE, or FUNCTION_DECL for the "outermost"
- function scope. Inlined functions are chained by this so that given
- expression E and its TREE_BLOCK(E) B, BLOCK_SUPERCONTEXT(B) is the scope
- in which E has been made or into which E has been inlined. */
+/* Either a BLOCK of the enclosing scope or FUNCTION_DECL for
+ the "outermost" function scope. In the middle end used to chain
+ scopes of functions inlined into their callers. */
#define BLOCK_SUPERCONTEXT(NODE) (BLOCK_CHECK (NODE)->block.supercontext)
/* Points to the next scope at the same level of nesting as scope NODE. */
#define BLOCK_CHAIN(NODE) (BLOCK_CHECK (NODE)->block.chain)
/* A BLOCK, or FUNCTION_DECL of the function from which a block has been
- inlined. In a scope immediately enclosing an inlined leaf expression,
- points to the outermost scope into which it has been inlined (thus
- bypassing all intermediate BLOCK_SUPERCONTEXTs). */
+ copied by inlining or cloning. */
#define BLOCK_ABSTRACT_ORIGIN(NODE) (BLOCK_CHECK (NODE)->block.abstract_origin)
#define BLOCK_ORIGIN(NODE) \
(BLOCK_ABSTRACT_ORIGIN(NODE) ? BLOCK_ABSTRACT_ORIGIN(NODE) : (NODE))
