JIT: Restore EH-region check in if-conversion flow validation

[Copilot]

A Fuzzlyn-generated repro hits assert(!block->HasFlag(BBF_DONT_REMOVE)) during the JIT's If conversion phase when the Then block is the start of a try region. Bisected to dea4756 (#125347), which simplified IfConvertCheckFlow and inadvertently dropped the BasicBlock::sameEHRegion check previously performed by IfConvertCheckInnerBlockFlow. Without it, if-conversion proceeds on a Then/Else block that begins an EH region, then trips the assert when later removing it.

Changes

• src/coreclr/jit/ifconversion.cpp — In OptIfConversionDsc::IfConvertCheckFlow, bail when falseBb (Then) or trueBb (Else, when present) is not in the same EH region as m_startBlock.
• src/tests/JIT/Regression/JitBlue/Runtime_127446/Runtime_127446.cs — Regression test using the original repro. The test source is added to the shared merged src/tests/JIT/Regression/Regression_o_3.csproj (alongside other JitBlue regression tests); no per-test csproj or environment variables are needed.

if (falseBb->GetUniquePred(m_compiler) == nullptr)
{
    return false;
}

// Then/Else are removed by if-conversion, so they must share m_startBlock's EH
// region; otherwise they may be a try/handler entry (BBF_DONT_REMOVE).
if (!BasicBlock::sameEHRegion(falseBb, m_startBlock))
{
    return false;
}

m_doElseConversion = trueBb->GetUniquePred(m_compiler) != nullptr;
m_finalBlock       = m_doElseConversion ? trueBb->GetUniqueSucc() : trueBb;

if (m_doElseConversion && !BasicBlock::sameEHRegion(trueBb, m_startBlock))
{
    return false;
}

Verified the assert reproduces on the unfixed JIT and is gone with the fix; the new test passes through the merged test runner (global::Runtime_127446.Runtime_127446.TestEntryPoint() → Passed).

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[BoyBaykiller]

Maybe I should just directly check for BBF_DONT_REMOVE. This handles BasicBlock::sameEHRegion and anything else...

[EgorBo]

@copilot please delete Runtime_127446.csproj, juse use the shared csproj, we don't need explicit env vars for this.

[Copilot]

@copilot please delete Runtime_127446.csproj, juse use the shared csproj, we don't need explicit env vars for this.

Done in 1a10c80 — removed Runtime_127446.csproj and added the test to the shared merged JIT/Regression/Regression_o_3.csproj. Verified it runs and passes through the merged runner (global::Runtime_127446.Runtime_127446.TestEntryPoint() → Passed).

Note

This reply was AI-generated by GitHub Copilot.