https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115260
Bug ID: 115260
Summary: Corruption of derived type data when array temporarys
of type occur
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: steve.mullerworth at metoffice dot gov.uk
Target Milestone: ---
Created attachment 58301
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58301&action=edit
Compile with -Og or more to illustrate issue
I have a 2D (or more than 2D) array of a derived type. The derived type
contains one or more allocatable arrays of reals or integers.
If I call a subroutine with a part of the 2D array *such that an array
temporary is created* then data in the arrays within the derived type are
corrupted on return: the first few items of data in each array are corrupted.
The example program demonstrates calling subroutines in a way that don't use
temporary arrays and then in a way that does use temporary arrays, printing the
arrays as it progresses. On return from the final call that results in array
temporaries, the issue is that the arrays of reals and integers have different
values in the first few elements.
The amount of corruption in the allocatable arrays appears to be a certain
number of bits, so a real64 has half the corruption of an integer32. The number
of bits seems platform dependent. Mosty 128 bits on Godbolt Compiler Explorer
and my desktop old-ish Intel (Intel(R) Xeon(R) Gold 6132 CPU @ 2.60GHz). But
256 bits on ARM Genoa (AMD EPYC 7763 64-Core) for some reason – it’s another
64-bit CPU.
Started happening from gcc10.2 up to head of trunk (according to the Compiler
Explorer). Affects -Og or above. -O0 is fine. Use -fcheck=all to show up
creation of array temporaries at last call.
Link to Compiler Explorer example:
https://godbolt.org/z/971evY8sn
