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[Stack Switching] Fix GUFA on continuations (#7824)
We must mark the blocks that Resumes target as receiving values, or else GUFA will think they are unreachable, and optimize them away.
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3 files changed

+164
-5
lines changed

3 files changed

+164
-5
lines changed

‎scripts/test/fuzzing.py‎

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Original file line numberDiff line numberDiff line change
@@ -114,6 +114,7 @@
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'vacuum-stack-switching.wast',
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'cont.wast',
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'cont_simple.wast',
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'gufa-cont.wast',
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'cont_many_unhandled.wast',
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# TODO: fix split_wast() on tricky escaping situations like a string ending
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# in \\" (the " is not escaped - there is an escaped \ before it)

‎src/ir/possible-contents.cpp‎

Lines changed: 31 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1291,14 +1291,40 @@ struct InfoCollector
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// TODO: optimize when possible
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addRoot(curr);
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}
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void visitResume(Resume* curr) {
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// TODO: optimize when possible
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addRoot(curr);
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}
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void visitResumeThrow(ResumeThrow* curr) {
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template<typename T> void handleResume(T* curr) {
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// TODO: optimize when possible
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addRoot(curr);
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// Connect handled tags with their branch targets, and materialize non-null
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// continuation values.
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auto numTags = curr->handlerTags.size();
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for (Index tagIndex = 0; tagIndex < numTags; tagIndex++) {
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auto tag = curr->handlerTags[tagIndex];
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auto target = curr->handlerBlocks[tagIndex];
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auto params = getModule()->getTag(tag)->params();
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// Add the values from the tag.
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for (Index i = 0; i < params.size(); i++) {
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if (isRelevant(params[i])) {
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info.links.push_back(
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{TagLocation{tag, i}, getBreakTargetLocation(target, i)});
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}
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}
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// Add the continuation. Its type is determined by the block we break to,
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// as the last result.
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auto targetType = findBreakTarget(target)->type;
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assert(targetType.size() >= 1);
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auto contType = targetType[targetType.size() - 1];
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auto location = getRootLocation(contType);
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info.links.push_back(
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{location, getBreakTargetLocation(target, params.size())});
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}
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}
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void visitResume(Resume* curr) { handleResume(curr); }
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void visitResumeThrow(ResumeThrow* curr) { handleResume(curr); }
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void visitStackSwitch(StackSwitch* curr) {
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// TODO: optimize when possible
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addRoot(curr);

‎test/lit/passes/gufa-cont.wast‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,132 @@
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;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
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;; RUN: foreach %s %t wasm-opt -all --gufa -S -o - | filecheck %s
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(module
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;; CHECK: (type $func (func))
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(type $func (func))
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;; CHECK: (type $cont (cont $func))
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(type $cont (cont $func))
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;; CHECK: (type $func-i32 (func (result i32)))
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(type $func-i32 (func (result i32)))
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;; CHECK: (type $cont-i32 (cont $func-i32))
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(type $cont-i32 (cont $func-i32))
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;; CHECK: (type $4 (func (result i32 (ref $cont))))
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;; CHECK: (elem declare func $cont $cont-i32)
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;; CHECK: (tag $tag (type $func))
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(tag $tag (type $func))
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;; CHECK: (tag $tag-i32 (type $func-i32) (result i32))
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(tag $tag-i32 (type $func-i32))
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;; CHECK: (export "resume" (func $resume))
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;; CHECK: (export "resume_throw" (func $resume_throw))
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;; CHECK: (export "resume-i32" (func $resume-i32))
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;; CHECK: (func $cont (type $func)
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;; CHECK-NEXT: (suspend $tag)
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;; CHECK-NEXT: )
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(func $cont
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;; Helper for below.
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(suspend $tag)
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)
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;; CHECK: (func $resume (type $func)
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;; CHECK-NEXT: (drop
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;; CHECK-NEXT: (block $block (result (ref $cont))
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;; CHECK-NEXT: (resume $cont (on $tag $block)
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;; CHECK-NEXT: (cont.new $cont
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;; CHECK-NEXT: (ref.func $cont)
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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;; CHECK-NEXT: (return)
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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(func $resume (export "resume")
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;; A continuation is created, it suspends, and we handle that. There is
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;; nothing to optimize or change here.
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(drop
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(block $block (result (ref $cont))
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(resume $cont (on $tag $block)
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(cont.new $cont
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(ref.func $cont)
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)
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)
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(return)
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)
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)
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)
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;; CHECK: (func $resume_throw (type $func)
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;; CHECK-NEXT: (drop
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;; CHECK-NEXT: (block $block (result (ref $cont))
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;; CHECK-NEXT: (resume_throw $cont $tag (on $tag $block)
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;; CHECK-NEXT: (cont.new $cont
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;; CHECK-NEXT: (ref.func $cont)
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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;; CHECK-NEXT: (return)
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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(func $resume_throw (export "resume_throw")
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;; As above, but with resume_throw.
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(drop
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(block $block (result (ref $cont))
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(resume_throw $cont $tag (on $tag $block)
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(cont.new $cont
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(ref.func $cont)
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)
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)
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(return)
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)
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)
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)
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;; CHECK: (func $cont-i32 (type $func-i32) (result i32)
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;; CHECK-NEXT: (suspend $tag)
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;; CHECK-NEXT: (unreachable)
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;; CHECK-NEXT: (unreachable)
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;; CHECK-NEXT: )
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(func $cont-i32 (result i32)
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;; Helper for below.
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(suspend $tag)
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(unreachable)
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)
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;; CHECK: (func $resume-i32 (type $func)
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;; CHECK-NEXT: (tuple.drop 2
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;; CHECK-NEXT: (block $block (type $4) (result i32 (ref $cont))
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;; CHECK-NEXT: (drop
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;; CHECK-NEXT: (resume $cont-i32 (on $tag-i32 $block)
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;; CHECK-NEXT: (cont.new $cont-i32
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;; CHECK-NEXT: (ref.func $cont-i32)
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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;; CHECK-NEXT: (return)
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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(func $resume-i32 (export "resume-i32")
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;; As above, but with more values sent than just the continuation.
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(tuple.drop 2
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(block $block (result i32 (ref $cont))
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(resume $cont-i32 (on $tag-i32 $block)
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(cont.new $cont-i32
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(ref.func $cont-i32)
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)
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)
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(return)
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)
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)
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)
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)
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