Bug ID: JDK-8253089 Windows (MSVC 2017) build fails after JDK-8243208

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JDK 16
16 b16Fixed

Tools summary:
* Environment:    cygwin version 3.1.7(0.340/5/3), 2020-08-22 17:48. Windows version 10.0.18363.1082. Root at /cygdrive/c/cygwin64
* Boot JDK:       openjdk version "14.0.1-internal" 2020-04-14  OpenJDK Runtime Environment (build 14.0.1-internal+0-adhoc..build)  OpenJDK 64-Bit Server VM (build 14.0.1-internal+0-adhoc..build, mixed mode, sharing)   (at /cygdrive/c/buildbot/jdks/jdk14)
* Toolchain:      microsoft (Microsoft Visual Studio 2017)
* C Compiler:     Version 19.16.27039 (at /cygdrive/c/progra~2/micros~1/2017/commun~1/vc/tools/msvc/1416~1.270/bin/hostx86/x64/cl)
* C++ Compiler:   Version 19.16.27039 (at /cygdrive/c/progra~2/micros~1/2017/commun~1/vc/tools/msvc/1416~1.270/bin/hostx86/x64/cl)

c:/buildbot/worker/build-jdkX-windows/build/src/hotspot/share/runtime/flags/jvmFlagLookup.cpp(54): error C2220: warning treated as error - no 'object' file generated
c:/buildbot/worker/build-jdkX-windows/build/src/hotspot/share/runtime/flags/jvmFlagLookup.cpp(54): warning C4307: '*': integral constant overflow
make[3]: *** [lib/CompileJvm.gmk:143: /cygdrive/c/buildbot/worker/build-jdkX-windows/build/build/windows-x86_64-server-fastdebug/hotspot/variant-server/libjvm/objs/jvmFlagLookup.obj] Error 1
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [make/Main.gmk:259: hotspot-server-libs] Error 2

Changeset: 3f455f09 Author: Aleksey Shipilev <shade@openjdk.org> Date: 2020-09-15 05:14:06 +0000 URL: https://git.openjdk.java.net/jdk/commit/3f455f09
15-09-2020
u2 matches the underlying storage type in the final table and avoids a few casts along the way. It looks safe to me to calculate hash code directly in u2 domain. But sure, if you have better suggestion, do tell in GH review. (That would need another few hours to verify, as my Windows VMs are very slow).
14-09-2020
This may be an example of https://developercommunity.visualstudio.com/content/problem/211134/unsigned-integer-overflows-in-constexpr-functionsa.html This would explain why using u2 would dodge the warning. (Though I don't think that's an actually good solution.) The currently overflowing arithmetic operations would be on the promoted u2 values, so won't overflow.
14-09-2020
The change above did not work too. I am trying to use "u2" consistently now...
14-09-2020
Testing this: diff --git a/src/hotspot/share/runtime/flags/jvmFlagLookup.cpp b/src/hotspot/share/runtime/flags/jvmFlagLookup.cpp index 8f628987f56..75693df7fa9 100644 --- a/src/hotspot/share/runtime/flags/jvmFlagLookup.cpp +++ b/src/hotspot/share/runtime/flags/jvmFlagLookup.cpp @@ -39,7 +39,7 @@ constexpr JVMFlagLookup::JVMFlagLookup() : _buckets(), _table(), _hashes() { for (int i = 0; i < NUM_BUCKETS; i++) { - _buckets[i] = -1; + _buckets[i] = (short)-1; } ALL_FLAGS(DO_FLAG,
14-09-2020
Nope, that patch does not work. And I am not sure why it would work, since it relates to "h", which is already unsigned int. EDIT: Ah, that's constexpr, so any related code might fail, gaah.
14-09-2020
Maybe it's complaining about this "" in jvmFlagLookup.hpp? How about this: static constexpr unsigned int hash_code(const char s, size_t len) { unsigned int h = 0; while (len -- > 0) { - h = 31h + (unsigned int) s; + h = ((unsigned int)31)h + (unsigned int) s; s++; } return h;
14-09-2020
The error above is from MSVC 2017. MSVC 2019 seems to compile this code fine. MSVC bug then?
14-09-2020
Another try seems to work. In review now: https://github.com/openjdk/jdk/pull/150
14-09-2020

Relates :	JDK-8243208 - Clean up JVMFlag implementation
Relates :	JDK-8253239 - Disable VS warning C4307