[LLVMbugs] [Bug 275] NEW: [llvmgcc] Local array initializers are expanded into huge amounts of code

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=275

           Summary: [llvmgcc] Local array initializers are expanded into
                    huge amounts of code
           Product: tools
           Version: 1.0
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: llvm-gcc
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sabre at nondot.org


In the following function, each initializer element is expanded into a
getelementptr/store pair, resulting in a TON of code.  This is a reduced &
simplified testcase from imagemagick, whose giant array is not nearly as
pointless as this one.

----
int test(int x) {
  const int array[] = {
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
     17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 17, 23, 123, 123, 49, 
   };
   return array[x];
} 
----

When the array has more than a few initializers, we should memcpy from a
statically initalized global variable into the array alloca.  Ideally we should
then be able to eliminate the alloca (in this case where the array is never
written to besides the memcpy), but that's an optimization, not a "cannot
compile the testcase because the compiler runs forever" bug.

-Chris



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