[LLVMdev] LLVM Loop Vectorizer puzzle

[maxs]

Hi,
     I have the llvm loop vectorizer to complie the following sample:
//=================

int test(int *a, int n) {

         for(int i = 0; i < n; i++) {

                   a[i] += i;

         }

         return 0;

}

//================
        The corresponded .ll file has a loop preheader:
//================

for.body.lr.ph:                                   ; preds = %entry
   %cnt.cast = zext i32 %n to i64
   %0 = and i32 %n, 7
   %n.mod.vf = zext i32 %0 to i64
   %n.vec = sub i64 %cnt.cast, %n.mod.vf
   %cmp.zero = icmp eq i32 %0, %n
   br i1 %cmp.zero, label %middle.block, label %vector.body
//================

        That is , if n <=7, the program will skip the vector.body. In 
LoopVectorize.cpp , I see the following code:
//================

             static cl::opt<unsigned>
TinyTripCountVectorThreshold("vectorizer-min-trip-count", cl::init(16), 
... );
//================

       The minimal loop count is 16. What is the "n<=7" meaning?   Thanks.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130523/24091e31/attachment.html>