[LLVMbugs] [Bug 6452] New: Prevent an input structure from being copied to the stack

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=6452

           Summary: Prevent an input structure from being copied to the
                    stack
           Product: libraries
           Version: 2.6
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: Register Allocator
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: llvm at henning-thielemann.de
                CC: llvmbugs at cs.uiuc.edu


Created an attachment (id=4347)
 --> (http://llvm.org/bugs/attachment.cgi?id=4347)
an example where values are copied from an input struct to the stack, although
they could remain in the input struct

I have a function definition like
  define i32 @_fun1(%param* noalias, i32, float* noalias)
that reads parameters from a struct type %param and writes results to a float
array of size with type i32. Now LLVM generates code that first copies all
parameters to the stack. This is correct in all circumstances but in my
application I can warrant that the parameter struct and the float array do not
overlap and thus the parameters could always be fetched directly from the
parameter struct. But maybe this isn't even a bug but a feature, because LLVM
expects faster memory access if all temporarily needed values are at one place
(on the stack)?

Maybe this is related to
http://llvm.org/bugs/show_bug.cgi?id=1819
http://llvm.org/bugs/show_bug.cgi?id=1821

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