On Mon, Jul 27, 2020 at 10:49 PM Jakub Jelinek via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > On Mon, Jul 27, 2020 at 09:53:31AM -0600, Martin Sebor via Gcc-patches wrote: > > Return a pointer P to a NUL-terminated string containing > > the sequence of bytes corresponding to the representation > > of the object referred to by SRC (or a subsequence of such > > bytes within it if SRC is a reference to an initialized > > constant array plus some constant offset). > > > > I.e., c_getstr returns a STRING_CST for arbitrary non-string > > constants. This enables optimizations like the by-pieces > > expansion of calls to raw memory functions like memcpy, or > > the folding of other raw memory calls like memchr with non- > > string arguments. > > > > c_getstr relies on string_constant for that. Restricting > > the latter function to just character types prevents these > > optimizations for zero-initialized constants of other types. > > A test case that shows the difference to the by-pieces > > expansion goes something like this: > > Having STRING_CST in the compiler with arbitrary array type is IMHO a very > bad idea, so if you want something like that, you should come up with a > different representation for that, not STRING_CSTs. > Because most of the compiler assumes STRING_CSTs are what it says, string > literals where elements are some kind of characters, don't have to be > narrow, but better should be integral. > Maybe returning a CONSTRUCTOR with no elements with the right type is a > better idea for that, that in the compiler stands for zero initialized > aggregate.
It's also a much shorter representation (that also works for strings, btw) if it is all about all-zero "constants". Richard. > Jakub >
