[LLVMbugs] [Bug 20044] New: Libcall simplification in -ffreestanding

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20044

            Bug ID: 20044
           Summary: Libcall simplification in -ffreestanding
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: llvm-bugs at quasiparticle.net
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Currently, clang disables libcall simplification entirely when called with
-ffreestanding, as is expected. clang also disables libcall simplification if
-fbuiltin is also given on the command line, contrary to what gcc does.

I fully agree with the default behaviour (-ffreestanding implies -fno-builtin),
but I also want to disable it in some circumstances. In freestanding mode,
folding memcpy and friends instead of generating calls is just as useful as in
hosted mode (except in the definition of those, of course). Allowing -fbuiltin
to enable libcall simplification on freestanding would be one way to do that,
or a new function attribute (I'd prefer that), or maybe something else
entirely.

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