[llvm-bugs] [Bug 51188] New: lib/clang/13.0.0/include/intrin.h is missing __readfsdword

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51188

            Bug ID: 51188
           Summary: lib/clang/13.0.0/include/intrin.h is missing
                    __readfsdword
           Product: libc++
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: brucedawson at chromium.org
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com

While trying to get V8 to compile without requiring windows.h for most
translation units I hit a problem on one build configuration where
__readfsdword is unavailable, despite including intrin.h. This happens when
intrin.h is included from
third_party/llvm-build/Release+Asserts/lib/clang/13.0.0/include/intrin.h.

I cannot reproduce this in a Chromium build but in a V8 stand-alone build it
can be reproduced with these gn args:

is_component_build = true
is_debug = true
symbol_level = 1
target_cpu = "x86"
use_goma = true
v8_enable_backtrace = true
v8_enable_google_benchmark = true
v8_enable_slow_dchecks = true

Many targets fail to build. One example is obj/v8_libbase/strings.obj.

The relevant section of intrin.h seems to be this block which has function
definitions for reading 1, 8, and 2 bytes, but not 4:

unsigned char __readfsbyte(unsigned long);
unsigned __int64 __readfsqword(unsigned long);
unsigned short __readfsword(unsigned long);

See the try jobs in https://chromium-review.googlesource.com/c/v8/v8/+/3042215
for an example of the failures, on the v8_win_compile_dbg bot.

https://bugs.llvm.org/show_bug.cgi?id=38726 looks similar, but different.

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