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Use exactness to optimize GUFA cone depth #7538

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Use exactness to optimize GUFA cone depth #7538

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f6db18c
Use exactness to optimize GUFA cone depth
tlively Apr 22, 2025
7f9201a
Move exact type handling to cone creation
tlively Apr 22, 2025
ee829fe
Merge branch 'main' into gufa-exact-cone
tlively Apr 29, 2025
68644ee
Merge branch 'main' into gufa-exact-cone
tlively Apr 29, 2025
687cb9e
Merge branch 'main' into gufa-exact-cone
tlively Apr 29, 2025
f54fe8f
Merge branch 'main' into gufa-exact-cone
tlively Apr 30, 2025
e451a08
Merge branch 'main' into gufa-exact-cone
tlively May 1, 2025
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Merge branch 'main' into gufa-exact-cone
tlively May 5, 2025
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Merge branch 'main' into gufa-exact-cone
tlively May 7, 2025
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Merge branch 'main' into gufa-exact-cone
tlively May 8, 2025
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Merge branch 'main' into gufa-exact-cone
tlively May 8, 2025
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Merge branch 'main' into gufa-exact-cone
tlively May 9, 2025
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8 changes: 6 additions & 2 deletions src/ir/possible-contents.h
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Original file line number Diff line number Diff line change
Expand Up @@ -128,7 +128,9 @@ class PossibleContents {

// Internal convenience for creating a cone type of unbounded depth, i.e., the
// full cone of all subtypes for that type.
static ConeType FullConeType(Type type) { return ConeType{type, FullDepth}; }
static ConeType FullConeType(Type type) {
return type.isExact() ? ExactType(type) : ConeType{type, FullDepth};
}

template<typename T> PossibleContents(T value) : value(value) {}

Expand Down Expand Up @@ -265,7 +267,9 @@ class PossibleContents {

// Returns whether the relevant cone for this, as computed by getCone(), is of
// full size, that is, includes all subtypes.
bool hasFullCone() const { return getCone().depth == FullDepth; }
bool hasFullCone() const {
return getCone().depth == (getType().isExact() ? 0 : FullDepth);
}
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Does this need to change? It seems odd to consider a code of depth 0 as "full".

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Yes, otherwise a bunch of assertions expecting full cone types started failing. I think it makes sense to make cone creation and inspection consistent in treating depth-0 cones for exact types as "full," so I think this is a better solution than going and changing those assertions.

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I'd like to understand this better - which assertions were those?

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@tlively tlively Apr 22, 2025 •
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The assertion at the top of PossibleContents::intersect.

// This does not yet handle all possible content.
assert(other.isFullConeType() || other.isLiteral() || other.isNone());

Looking deeper into PossibleContents::intersect and the other methods it calls, it's a little difficult to tell whether they do the right thing with exact types. I propose 1) moving forward with this change as-is to see if further fuzzing with exact types turns up any issues and 2) adding more possible-contents gtests covering exact types in a follow-up.

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Hmm, that assert looks suspicious to me... I'd rather investigate that first, but I don't feel strongly.

If you want to land this quickly to unblock other stuff, how about doing the reverse: modify the assert to allow either a full cone or an exact type, so we don't need to modify hasFullCone? I can also take a look at the PossibleContents code if you want.

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No rush to land this. I can reorder things to avoid getting blocked. I do think it would be weird if a value created by fullConeType did not satisfy hasFullCone or isFullCone, though.

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Yeah, we should rename fullConeType probably. Really what it does now is create a cone based on the type. Just coneType might be enough.


// Returns whether this is a cone type and also is of full size. This differs
// from hasFullCone() in that the former can return true for a global, for
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71 changes: 71 additions & 0 deletions test/lit/passes/gufa-cast-all-exact.wast
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Expand Up @@ -139,6 +139,77 @@
)
)

(module
;; CHECK: (type $super (sub (struct)))
;; NO_CD: (type $super (sub (struct)))
(type $super (sub (struct)))
(type $sub (sub $super (struct)))

;; CHECK: (import "" "a" (global $exact-a (ref (exact $super))))
;; NO_CD: (import "" "a" (global $exact-a (ref (exact $super))))
(import "" "a" (global $exact-a (ref (exact $super))))
;; CHECK: (import "" "b" (global $exact-b (ref (exact $super))))
;; NO_CD: (import "" "b" (global $exact-b (ref (exact $super))))
(import "" "b" (global $exact-b (ref (exact $super))))
;; CHECK: (import "" "x" (global $x i32))
;; NO_CD: (import "" "x" (global $x i32))
(import "" "x" (global $x i32))

;; CHECK: (func $get-exact (type $1) (result (ref $super))
;; CHECK-NEXT: (select (result (ref (exact $super)))
;; CHECK-NEXT: (global.get $exact-a)
;; CHECK-NEXT: (global.get $exact-b)
;; CHECK-NEXT: (global.get $x)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; NO_CD: (func $get-exact (type $1) (result (ref $super))
;; NO_CD-NEXT: (select (result (ref (exact $super)))
;; NO_CD-NEXT: (global.get $exact-a)
;; NO_CD-NEXT: (global.get $exact-b)
;; NO_CD-NEXT: (global.get $x)
;; NO_CD-NEXT: )
;; NO_CD-NEXT: )
(func $get-exact (result (ref $super))
(select (result (ref (exact $super)))
(global.get $exact-a)
(global.get $exact-b)
(global.get $x)
)
)

;; CHECK: (func $cast-sub (type $2)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (ref.cast (ref (exact $super))
;; CHECK-NEXT: (call $get-exact)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (unreachable)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; NO_CD: (func $cast-sub (type $2)
;; NO_CD-NEXT: (drop
;; NO_CD-NEXT: (block
;; NO_CD-NEXT: (drop
;; NO_CD-NEXT: (call $get-exact)
;; NO_CD-NEXT: )
;; NO_CD-NEXT: (unreachable)
;; NO_CD-NEXT: )
;; NO_CD-NEXT: )
;; NO_CD-NEXT: )
(func $cast-sub
(drop
;; We should be able to infer that this cast will not succeed and insert an
;; unreachable after it.
(ref.cast (ref $sub)
(call $get-exact)
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Hmm, why doesn't this work without exact types? GUFA's depth zero cone should have had enough information already.

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Note that the sources are imports, not allocations, so without the new changes, GUFA doesn't know that it can use 0-depth cones for those imports.

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Oh right, thanks!

)
)
)
)

(module
;; CHECK: (type $foo (sub (struct (field i32))))
;; NO_CD: (type $foo (sub (struct (field i32))))
Expand Down
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