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

Kim Barrett kim.barrett at oracle.com
Thu Apr 16 17:34:10 UTC 2015

On Apr 16, 2015, at 4:50 AM, Lindenmaier, Goetz <goetz.lindenmaier at sap.com> wrote:

the IBM docu says that notreturn affects only warnings about uninitialized variables, not about missing returns.

I would summarize it as saying it does affect ununitialized variable warnings, and as being silent on the subject of missing returns.

It also says that registers are not stored on a call. http://publibfp.boulder.ibm.com/epubs/pdf/c1473260.pdf page 193.

Actually, it says registers saved by the caller might not be restored before the call.

For the compiler flags and warnings I get see the compile output below.

The missing return warnings are quite disappointing, even to the level of a bug. Though the feature documentation is so light, it could arguably do almost anything.

XLC appears to provide at least three mechanisms for indicating a function doesn't return. The attribute method has the weakest description: "indicate to the compiler that the function is not intended to return." The others are

_Noreturn function attribute (similar to inline) - "declares a function that does not return to its caller." Added by C11 and requires special compiler options to enable.

#pragma leaves(function_name, ...) - "Informs the compiler that a named function never returns to the instruction following a call to that function."

Goetz, if you have some time (yeah, right), it might be interesting to find out if either of the other two behave any differently with regard to missing return warnings.

I will be sad if this proposed change has to be dropped because an otherwise well-reputed compiler was so lame in this respect. I really dislike dummy return statements and not having -Wuninitialized turned on.

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