[PATCH] [SLPVectorizer] Reorder operands of shufflevector if it can result in a vectorized code.

[Karthik Bhat]

Hi Michael,
While still at this patch fix one more issue(small change) originally present in reorderInputsAccordingToOpcode.

In  reorderInputsAccordingToOpcode AllSameOpcodeLeft and AllSameOpcodeLeft should return true if all the opCode on left and right respectively are same. But alas in the code we can see that in the loop we are resetting the value to-

  AllSameOpcodeLeft = I0;
  AllSameOpcodeRight = I1;

for each iteration. As a result we end up checking if the last 2 instructions have the same opcode in left and right.
As a result a code such as -

  void foo(float* restrict a,float* restrict b,float* restrict c, float* restrict d)
  {
    a[0] = (b[0]+c[0])+d[0];
    a[1] = d[1]+(b[1]+c[1]);
    a[2] = (b[2]+c[2])+d[2];
    a[3] = (b[3]+c[3])+d[3];
  }

results in unoptimal vectorization as it considers all opcode on left and right to be same(since the last 2 have same opcode on left and right) and doesn't reorder the 2nd instruction which could have resulted in a better vectorized code.
This updated patch fixes this issue and added a test case for the same.

Please let me know your inputs on the same.

Thanks and Rergards
Karthik Bhat


REPOSITORY
  rL LLVM

http://reviews.llvm.org/D6677

Files:
  lib/Transforms/Vectorize/SLPVectorizer.cpp
  test/Transforms/SLPVectorizer/X86/addsub.ll
  test/Transforms/SLPVectorizer/X86/operandorder.ll

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