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[6.2] MoveOnlyChecker: avoid dangling reference in custom alloc #84937

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Merged
merged 1 commit into from
Oct 16, 2025
Merged

[6.2] MoveOnlyChecker: avoid dangling reference in custom alloc #84937

merged 1 commit into from
Oct 16, 2025

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kavon
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@kavon kavon commented Oct 15, 2025 •
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  • Explanation: Fixes a use-after-free in the MoveOnlyChecker
  • Scope: Can cause crashes of the compiler on code using ~Copyable types within a large-enough function.
  • Issues: rdar://162440304
  • Original PRs: MoveOnlyChecker: avoid dangling reference in custom alloc #84934
  • Risk: Low. The asserts I added would only catch further uses of uninitialized memory.
  • Testing: Manual testing within a configuration that would reproduce the crash 100% of the time. Patch resolves that crash.
  • Reviewers: @jckarter

@kavon
MoveOnlyChecker: avoid dangling reference in custom alloc
743599b 
The AvailableValueStore maintains stable spans of SILValues,
one span (effectively a MutableArrayRef) per basic block, that
is preallocated for performance.

This patch fixes an issue where _a pointer_ to a span is vended from
`AvailableValueStore::get` and that pointer is into storage within
a DenseMap, which can reallocate and invalidate all such pointers.

There's no reason to be returning a pointer to a MutableArrayRef,
aka AvailableValues, so I've simply stripped off that indirection to
fix this issue.

resolves rdar://162440304

(cherry picked from commit d1f3f84)
@kavon kavon requested a review from a team as a code owner October 15, 2025 22:05
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kavon commented Oct 15, 2025

@swift-ci test

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kavon commented Oct 15, 2025

@swift-ci Please Build Toolchain Ubuntu 24.04

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kavon commented Oct 16, 2025

Looks like the toolchain build failed with an unrelated issue:

******************** TEST 'Swift(linux-x86_64) :: Interop/CxxToSwiftToCxx/span/span-execution.cpp' FAILED ********************
... 
 /home/build-user/build/buildbot_linux/swift-linux-x86_64/test-linux-x86_64/Interop/CxxToSwiftToCxx/span/Output/span-execution.cpp.tmp/header.h:8:44: error: unknown type name 'uint8_t'
     8 |   using SpanOfConstUInt8 = std::span<const uint8_t>;
       |                                            ^
 In file included from /home/build-user/build/buildbot_linux/swift-linux-x86_64/test-linux-x86_64/Interop/CxxToSwiftToCxx/span/Output/span-execution.cpp.tmp/use-span.cpp:3:
 /home/build-user/build/buildbot_linux/swift-linux-x86_64/test-linux-x86_64/Interop/CxxToSwiftToCxx/span/Output/span-execution.cpp.tmp/UseSpan.h:4111:58: error: no member named 'SpanOfConstUInt8' in namespace 'ns'
  4111 | inline const constexpr bool isUsableInGenericContext<ns::SpanOfConstUInt8> = true;
       |                                                      ~~~~^
 /home/build-user/build/buildbot_linux/swift-linux-x86_64/test-linux-x86_64/Interop/CxxToSwiftToCxx/span/Output/span-execution.cpp.tmp/UseSpan.h:4113:30: error: no member named 'SpanOfConstUInt8' in namespace 'ns'
  4113 | struct TypeMetadataTrait<ns::SpanOfConstUInt8> {
       |                          ~~~~^
 /home/build-user/build/buildbot_linux/swift-linux-x86_64/test-linux-x86_64/Interop/CxxToSwiftToCxx/span/Output/span-execution.cpp.tmp/UseSpan.h:4120:57: error: no member named 'SpanOfConstUInt8' in namespace 'ns'
  4120 | inline const constexpr bool isSwiftBridgedCxxRecord<ns::SpanOfConstUInt8> = true;
       |                                                     ~~~~^
 4 errors generated.

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kavon commented Oct 16, 2025

@swift-ci Please Build Toolchain UBI9

@kavon kavon enabled auto-merge October 16, 2025 19:18
@kavon kavon merged commit 24154e3 into swiftlang:release/6.2 Oct 16, 2025
5 of 7 checks passed
@kavon kavon deleted the 6.2-the-realloc-strikes-back-rdar162440304 branch October 16, 2025 20:35
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@hborla hborla hborla approved these changes

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