RFR: 8371431: Warning message when turning off CompactStrings

[Chen Liang]

On Mon, 27 Oct 2025 01:26:18 GMT, Shaojin Wen <swen at openjdk.org> wrote:

> A warning message should be given before removing the CompactStrings off option.

I think the code change looks like:

diff --git a/src/hotspot/cpu/arm/globals_arm.hpp b/src/hotspot/cpu/arm/globals_arm.hpp
index 363a9a2c25c..d64615dd142 100644
--- a/src/hotspot/cpu/arm/globals_arm.hpp
+++ b/src/hotspot/cpu/arm/globals_arm.hpp
@@ -69,7 +69,7 @@ define_pd_global(bool,  PreserveFramePointer,     false);
 define_pd_global(uintx, TypeProfileLevel, 0);
 
 // No performance work done here yet.
-define_pd_global(bool, CompactStrings, false);
+define_pd_global(bool, CompactStrings, true);
 
 define_pd_global(intx, InitArrayShortSize, 8*BytesPerLong);
 
diff --git a/src/hotspot/share/runtime/arguments.cpp b/src/hotspot/share/runtime/arguments.cpp
index 0d92f22af79..ac9eb7b6932 100644
--- a/src/hotspot/share/runtime/arguments.cpp
+++ b/src/hotspot/share/runtime/arguments.cpp
@@ -541,6 +541,7 @@ static SpecialFlag const special_jvm_flags[] = {
 
   // -------------- Obsolete Flags - sorted by expired_in --------------
 
+  { "CompactStrings",                JDK_Version::jdk(25),  JDK_Version::jdk(27), JDK_Version::jdk(28) },
 #ifdef LINUX
   { "UseOprofile",                  JDK_Version::jdk(25), JDK_Version::jdk(26), JDK_Version::jdk(27) },
 #endif


And backport the arguments.cpp but not globals_arm back to 25 updates.

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PR Comment: https://git.openjdk.org/jdk/pull/27995#issuecomment-3453150014