On Sun, 13 Feb 2022 10:58:19 GMT, Andrew Haley <a...@openjdk.org> wrote:
>> Jatin Bhateja has updated the pull request with a new target base due to a >> merge or a rebase. The incremental webrev excludes the unrelated changes >> brought in by the merge/rebase. The pull request contains four additional >> commits since the last revision: >> >> - 8279508: Adding vectorized algorithms to match the semantics of rounding >> operations. >> - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8279508 >> - 8279508: Adding a test for scalar intrinsification. >> - 8279508: Auto-vectorize Math.round API > > src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp line 4066: > >> 4064: } >> 4065: >> 4066: void >> C2_MacroAssembler::vector_cast_double_special_cases_evex(XMMRegister dst, >> XMMRegister src, XMMRegister xtmp1, > > What does this do? Comment, even pseudo code, would be nice. > Hi, IIRC for evex encoding you can embed the RC control bit directly in the > evex prefix, removing the need to rely on global MXCSR register. Thanks. Hi @merykitty , You are correct, we can embed RC mode in instruction encoding round instructions (towards -inf,+inf, zero). But to match the semantics of Math.round API one needs to add 0.5[f] to input value and then perform rounding over resultant value, which is why @sviswa7 suggested to use a global rounding mode driven by MXCSR.RC so that intermediate floating inexact values also are resolved as desired, but OOO execution may misplace LDMXCSR and hence may have undesired side effects. ------------- PR: https://git.openjdk.java.net/jdk/pull/7094
