RFR: 8313882: Fix -Wconversion warnings in runtime code [v2]

[Dean Long]

On Tue, 8 Aug 2023 20:09:56 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Here are fixes to silence -Wconversion warnings in runtime code.  Use direct cast for 64 bit int to double, otherwise default to checked_cast<>.  I changed the declaration of _held_monitor_count and _jni_monitor count to intx to fix cascade of warnings coming from this.
>> 
>> src/hotspot/share/runtime/synchronizer.cpp:1802:41: warning: conversion from 'intx' {aka 'long int'} to 'int' may change value [-Wconversion]
>>  1802 |     _thread->dec_held_monitor_count(rec + 1);
>>       |                                     ~~~~^~~
>> 
>> Tested with tier1-4 on linux-x64-debug and windows-x64-debug and tier1 on Oracle supported platforms.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Make bytecode.hpp index() functions return u2 not long.

src/hotspot/share/runtime/objectMonitor.hpp line 238:

> 236:   //
> 237:   #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \
> 238:     ((in_bytes(ObjectMonitor::f ## _offset())) - (unsigned)markWord::monitor_value)

This makes it int vs uint (-Wsign-conversion warning), and assumes the range of monitor_value.
One option is to narrow the type of monitor_value.  Option 2, cast the lhs to uintptr_t.  Option 3, use offset_of instead of signed ByteSize.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15177#discussion_r1287727808