[llvm-bugs] [Bug 41069] New: multiple isnan() checks enhancement

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41069

            Bug ID: 41069
           Summary: multiple isnan() checks enhancement
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: kobalicek.petr at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

It would be nice if clang/LLVM can merge multiple isnan checks into `ucomisd a,
b`. Consider the following C++ Code:

#include <cmath>
#include <algorithm>

bool isNaN(double a, double b, double c, double d) {
  return std::isnan(a) |
         std::isnan(b) |
         std::isnan(c) |
         std::isnan(d) ;
}

Clang Output
------------

isNaN(double, double, double, double):
        ucomisd xmm0, xmm1  ## THIS IS OKAY
        setp    al
        ucomisd xmm2, xmm2  ## HERE IS SOME PROBLEM
        setp    cl
        or      cl, al
        ucomisd xmm3, xmm3
        setp    al
        or      al, cl
        ret

GCC Output
----------

isNaN(double, double, double, double):
        ucomisd xmm0, xmm1
        setp    al
        ucomisd xmm2, xmm3
        setp    dl
        or      eax, edx
        ret

It seems that the pattern is already recognized but not applied to second and
third isnan checks.

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