[llvm-dev] Register Spill Caused by the Reassociation pass

[Haicheng Wu via llvm-dev]

Hi Sanjay,

 

I observed some extra register spills when applying the reassociation pass
on spec2006 benchmarks and I would like to listen to your advice.  

 

For example, function get_new_point_on_quad() of tria_boundary.cc in
spec2006/dealII has a sequences of code like this

 

.

X=a+b

.

Y=X+c

.

Z=Y+d

.

 

There are many other instructions between these float adds.  The
reassociation pass first swaps a and c when checking the second add, and
then swaps a and d when checking the third add.  The transformed code looks
like

 

.

X=c+b

.

Y=X+d

.

Z=Y+a

 

a is pushed all the way down to the bottom and its live range is much larger
now.  

 

Best,

 

Haicheng

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