[LLVMbugs] [Bug 2067] New: Loop unroller heuristics are over-aggressive with calls

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=2067

           Summary: Loop unroller heuristics are over-aggressive with calls
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sharparrow1 at yahoo.com
                CC: llvmbugs at cs.uiuc.edu


Testcase:
void a(int a,int b,int c,int d,int e,int f,int g);
void b(void) {for (int i = 0; i < 20; i++)  a(1,2,3,4,5,6,7);}

This snippet of C code produces about 160 lines of x86 code using clang
-emit-llvm-bc | opt -std-compile-opts | llc.  I'm pretty sure this is due to
the loop unroller inaccurately predicting the cost of a call.


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