chakra-core/ChakraCore

Wrong Assertion in GlobOpt::CollectMemOpInfo

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#6,476 opened on Jul 1, 2020

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BugLinuxgood first issue

Description

Hello, running following code in ch 1.11.19 debug version. An Assertion will be throw.

'use strict';
function func(b, c) {
    b[0] = c;
}
function main() {
    let b = new Uint32Array(100);

    for (let i = 0; i < 1000; i++) {
        i += 1;
        i += 0;
        func(b, {});
    }
}
main();

Output:

ASSERTION 19136: (...\chakracore-1.11.19\lib\backend\globopt.cpp, line 2325) !instr->GetDst() || instr->m_opcode == Js::OpCode::IncrLoopBodyCount || !loop->memOpInfo || (instr->m_opcode == Js::OpCode::Ld_I4 && prevInstr && (prevInstr->m_opcode == Js::OpCode::Add_I4 || prevInstr->m_opcode == Js::OpCode::Sub_I4) && instr->GetSrc1()->IsRegOpnd() && instr->GetDst()->IsRegOpnd() && prevInstr->GetDst()->IsRegOpnd() && instr->GetDst()->GetStackSym() == prevInstr->GetSrc1()->GetStackSym() && instr->GetSrc1()->GetStackSym() == prevInstr->GetDst()->GetStackSym()) || !loop->memOpInfo->inductionVariableChangeInfoMap->ContainsKey(GetVarSymID(instr->GetDst()->GetStackSym()))
 Failure: (!instr->GetDst() || instr->m_opcode == Js::OpCode::IncrLoopBodyCount || !loop->memOpInfo || (instr->m_opcode == Js::OpCode::Ld_I4 && prevInstr && (prevInstr->m_opcode == Js::OpCode::Add_I4 || prevInstr->m_opcode == Js::OpCode::Sub_I4) && instr->GetSrc1()->IsRegOpnd() && instr->GetDst()->IsRegOpnd() && prevInstr->GetDst()->IsRegOpnd() && instr->GetDst()->GetStackSym() == prevInstr->GetSrc1()->GetStackSym() && instr->GetSrc1()->GetStackSym() == prevInstr->GetDst()->GetStackSym()) || !loop->memOpInfo->inductionVariableChangeInfoMap->ContainsKey(GetVarSymID(instr->GetDst()->GetStackSym())))
FATAL ERROR: ch.exe failed due to exception code c0000420

I think this is likely just a wrong assertion since the assumption strict too much, may miss some cases. https://github.com/microsoft/ChakraCore/blob/33db8efd9f02cd528a7305391d7d10765a2e85f3/lib/Backend/GlobOpt.cpp#L2360-2374

ISec Lab 2020.7.1

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Tech stack
cpp
Domain
backend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++ knowledgeunderstanding of JIT compiler optimizations
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Reproduce the assertion failure using the provided JavaScript code in ChakraCore debug build. Examine the assertion at GlobOpt.cpp line 2360-2374 to understand the assumed invariant. The issue suggests the assertion is too strict; consider removing or relaxing the condition to handle cases where the induction variable change info map does not contain the expected key. Verify the fix by running the test case and ensuring no regression.