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<div>Hi,</div>
<div> </div>
<div>I analyzed the folding DAG nodes algorithm in LLVM, compared to code generated by Intel compiler and got into conclusion that the LLVM code is not always optimal.</div>
<div>This is an example:</div>
<div> </div>
<div> %b1 = fadd <8 x float> %a1, <float AAA, float AAA, float AAA, float AAA, float AAA, float AAA, float AAA, float AAA ></div>
<div> %b2 = fadd <8 x float> %a2, <float AAA, float AAA, float AAA, float AAA, float AAA, float AAA, float AAA, float AAA ></div>
<div> %c = fmul <8 x float> %b1, %b2</div>
<div> </div>
<div>The result (1) bellow is not better than (2), because loading constant is not a problem, but spilling %ymm2 that may be required in (1) is not cheap.</div>
<div> </div>
<div>(1)</div>
<div> vmovaps .LCPI1_0(%rip), %ymm2</div>
<div> vaddps %ymm2, %ymm1, %ymm1</div>
<div> vaddps %ymm2, %ymm0, %ymm0</div>
<div> vmulps %ymm1, %ymm0, %ymm0</div>
<div> </div>
<div>(2)</div>
<div> vaddps .LCPI1_0(%rip), %ymm1, %ymm1</div>
<div> vaddps .LCPI1_0(%rip), %ymm0, %ymm0</div>
<div> vmulps %ymm1, %ymm0, %ymm0</div>
<div> </div>
<div>In the attached patch I did a minor thing that does not change the current algorithm, but allows to add some target-specific analysis.</div>
<div> </div>
<div>Please review.</div>
<div> </div>
<div>Thank you.</div>
<div> </div>
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<li><b><i> Elena</i></b></li></span></font>
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