Hi Harald, How did we miss that one for so long? This is certainly OK for mainline and, I would suggest, 14-branch.
Thanks for the patch. Paul On Sun, 19 Jan 2025 at 20:42, Harald Anlauf <anl...@gmx.de> wrote: > Dear all, > > this patch addresses a long-standing difference between gfortran and > other brands: when an array actual argument was passed to a procedure, > and the dummy argument had no intent specified, we would often create > packing and unpacking code. Only the case of the dummy argument > having intent(in) did avoid the unpacking. > > This resulted in the user experience that passing an array having the > PARAMETER attribute, i.e. a named constant that gcc could place in > read-only memory, was generating a segfault at runtime even if the > dummy argument was not modified in the invoked procedure. It therefore > was often not possible passing such an argument to a procedure without > explicitly requiring a temporary that might not be needed. (*) > > Other brands tested do not crash: > > (1) Intel, Nvidia, AMD flang, g95 seem to not put PARAMETER into read-only > memory. One can write code by lying to the compiler and modify the > array values. > > (2) NAG appears to prevent modification of variables with the PARAMETER > attribute. Code that lies to the compiler seems to have no effect, > but that compiler has a checking option that detects an illegal > assignment in the called procedure. > > The proposal is to simply not generate the unpacking / copying-back code > if the actual argument has the PARAMETER attribute. Non-conforming code > should rather be either detected at compile-time (which we do to a > reasonable extent), or we might add (in the future) new checking code > that detects modification of the dummy similar to case (2) above. > (We do something like this e.g. for do-loop indices passed as actual > arguments). > > How do you think of this approach? > > BTW: attached patch regtests fine on x86_64-pc-linux-gnu. ON for mainline? > > Thanks, > Harald > > (*) There is a missed-optimization in that we do not simply create > suitable array descriptors when passing to assumed-shape dummies, > which may avoid the packing. > >
