Re: [PATCH] Fix PR30028, fold sin, cos to sincos on the tree-level

[Paolo Bonzini <paolo dot bonzini at lu dot unisi dot ch>]

> I'll try to re-work it after vacation and if the canonicalization patch
> goes in.  Of course I still have the plan to teach VN/PRE to do this
> transformation by value-numbering sin (x) as IMAGPART_EXPR <cexpi (x)>
> and cos (x) as REALPART_EXPR <cexpi (x)> and teaching insertion and
> expression re-constructing to deal with value-numbers without a leader.

I would do something much simpler, using a dominator walk.  Sines and 
cosines are complicated enough (and infrequent enough) that they do not 
require the *post*dominator magic needed for reciprocals.

For every basic block, check if it invokes sin and cos on the same 
argument, and if so put a cexpi before the first invocation, and rewrite 
the others to REALPART_EXPRs or IMAGPART_EXPRs.  Put the argument in a 
hash table mapping the argument to the cexpi statement.  You may want to 
take a look at my pointer_map patch.  :-)

When you find a sin or cos, look up its argument in the hash table.  Use 
bb_for_stmt to check if the sincos really dominates the current basic 
block, and if so rewrite the sin or cos to the REALPART_EXPR or 
IMAGPART_EXPR.

It will catch most occurrences.  I wonder in fact if the dominator walk 
catches more occurrences than just looking for a sin and a cos in the 
same basic block (and relying on PRE to eliminate redundant cexpi's, but 
not redundant sin's and cos's).

Paolo