[LLVMdev] [Loop Vectorize] Question on -O3

maxs xtxwy.ustc at gmail.com
Tue Jul 2 00:49:49 PDT 2013

    When I use "-loop-vectorize" to vectorize a loop as below:
void bar(float *A, float* B, float K, int start, int end) {
   for (int i = start; i < end; ++i)
     A[i] *= B[i] + K;
   First, I use "*clang -O0 -emit-llvm -S bar.c -o bar.l*" to emit the 
.l file.
   Then I use "*opt -loop-vectorize -S bar.l -o bar.v.l*". 
Unfortunately, the vectorization don't work. But I use "*opt -O3 
-loop-vectorize -S bar.l -o bar.v.l*" and it works.
   My question is: What the information needed by "*-loop-vectorize*" 
the "*-O3*" provides? Thanks.
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