8065585: Change ShouldNotReachHere() to never return (original) (raw)

Lindenmaier, Goetz goetz.lindenmaier at sap.com
Wed Apr 15 14:54:28 UTC 2015

Hi Stefan,

Thanks for doing this fix, I would appreciate this cleanup a lot. I just built it on aix. So far, the attribute unfortunately does not suppress the warnings. I'll investgate this some more ...

Best regards, Goetz.

-----Original Message----- From: hotspot-dev [mailto:hotspot-dev-bounces at openjdk.java.net] On Behalf Of Stefan Karlsson Sent: Mittwoch, 15. April 2015 12:49 To: hotspot-dev Source Developers Subject: RFR: 8065585: Change ShouldNotReachHere() to never return

Hi,

Today the it's possible for the code to return out from ShouldNotReachHere() calls. This sometimes forces us to add return statements and assignments to parts of the code where it they don't make sense. By telling the compiler that ShouldNotReachHere is a dead end, we can get rid of these unnecessary constructs.

For example:

  1. We could get rid of return statements after ShouldNotReachHere():

bool is_marked() { // actual code here

// Execution path that "should not" happen. ShouldNotReachHere(); return false; }

  1. The following code will actually use an uninitialized value today. The compiler will find this if we turn on -Wuninitialized. But if we change ShouldNotReachHere() to not return, the compiler will stop complaining because report(type) will never be called with an uninitialized value:

int type; switch (value) { case TYPE_OOP: type = 0; break; case TYPE_KLASS: type = 1; break; default: ShouldNotReachHere(); } report(type)

The patch changes the following functions and defines to never return:

but leaves the following unchanged:

We might want to change the the behavior of Unimplemented() and Untested(...), but they are used a lot in compiler code, so I've not changed them for this patch. There has been request to leave guarantee(...) unchanged so that they can be turned off in production code.

I had to change some instance of ShouldNotReachHere() in destructors, because the VS C++ compiler complained about potential memory leaks.

http://cr.openjdk.java.net/~stefank/8065585/webrev.01/ https://bugs.openjdk.java.net/browse/JDK-8065585

Thanks, StefanK

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