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  1. JDK
  2. JDK-8288564

C2: LShiftLNode::Ideal produces wrong result after JDK-8278114

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      Description

        JDK-8278114 converts "(x + x) << c0" into "x << (c0 + 1)" for a long shift. However, that is not correct if c0 is 63:

        (1 + 1) << 63 is converted to (1 << 1) << 63
        = 1 << 64 = 1 << 0 [according to the Java spec we only consider the six lowest-order bits of the right-hand operand (i.e. 64 = 0b10000000 & 0b0111111 = 0)]
        = 1

        while

        (1 + 1) << 63 = 2 << 63 = 0

        which is different. We should exclude the optimization added by JDK-8278114 if c0 = 63.

        Integer shifts are note affected since we only apply the optimization for shift values smaller than 16.

        This was found by the Java Fuzzer.

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            Backport - A issue that is required to port a Bug or Feature into another product release. This issue type is generally associated with the main Bug/Feature to represent each individual release of the port. JDK-8288775 C2: LShiftLNode::Ideal produces wrong result after JDK-8278114

            • P2 - Crashes, loss of data, severe memory leak.
            • Resolved

            Backport - A issue that is required to port a Bug or Feature into another product release. This issue type is generally associated with the main Bug/Feature to represent each individual release of the port. JDK-8291099 C2: LShiftLNode::Ideal produces wrong result after JDK-8278114

            • P2 - Crashes, loss of data, severe memory leak.
            • Resolved

            Backport - A issue that is required to port a Bug or Feature into another product release. This issue type is generally associated with the main Bug/Feature to represent each individual release of the port. JDK-8291267 C2: LShiftLNode::Ideal produces wrong result after JDK-8278114

            • P2 - Crashes, loss of data, severe memory leak.
            • Resolved
            relates to

            Enhancement - null JDK-8278114 New addnode ideal optimization: converting "x + x" into "x << 1"

            • P4 - Minor loss of function, or other problem where easy workaround is present.
            • Resolved
            links to

            Commit Commit openjdk/jdk19/ed714af8

            Review Review openjdk/jdk19/29

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                chagedorn Christian Hagedorn
                chagedorn Christian Hagedorn
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