[9] RFR(M): 8076373: In 32-bit VM interpreter and compiled code process signaling NaN values inconsistently

[Vladimir Kozlov]

I think this is good. You need second review since changes are big and 
complex.

Thanks,
Vladimir

On 8/7/15 6:14 AM, Zoltán Majó wrote:
> Hi,
>
>
> please review the following patch for JDK-8076373.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8076373
>
>
> Problem: On x86_32 systems with XMM instructions available, the
> compilers and the interpreter behave inconsistently as far as signalling
> NaNs (sNaNs) are concerned. For example, the following statement||
>
> start == doubleToRawLongBits(longBitsToDouble(start))
>
> can be true or false, assuming that the variable 'start' contains a bit
> pattern corresponding to a sNaN.
>
> The result is true if the statement is executed by compiled code and
> longBitsToDouble/doubleToRawLongBits have been replaced by compiler
> intrinsics. The result is false if the native library version of the
> functions is used (either by compiled or by interpreted code).
>
> The inconsistency happens because the interpreter/native ABI relies on
> x87 instructions to process floating point numbers, whereas the
> compilers use XMM registers for the same purpose. x87 instructions
> silently convert signaling NaNs to quiet NaNs, XMM instructions preserve
> sNaNs.
>
>
> Solution:
> - Add intrinsics (stubs) for java.lang.Float.intBitsToFloat,
> java.lang.Float.floatToRawIntBits, java.lang.Double.longBitsToDouble,
> and java.lang.Double.doubleToRawLongBits. The stubs use XMM registers
> and therefore preserve sNaNs. The stubs are used by both the interpreter
> and the compilers.
> - Change the interpreter to use XMM registers instead of x87 registers
> to internally cache floating point values. As a result, sNaNs are
> preserved within the interpreter.
>
>
> Webrev:
> http://cr.openjdk.java.net/~zmajo/8076373/webrev.00/
>
> Testing:
> - JPRT run, testset hotspot (including the newly added test,
> NaNTest.java); all tests pass;
> - all JTREG tests in hotspot/test on x86_32 and x86_64; all tests pass
> that pass with the default version of the VM.
>
> Thank you and best regards,
>
>
> Zoltan
>