Sethi–Ullman algorithm: Difference between revisions

Revision as of 17:11, 12 November 2017

Revision as of 18:10, 12 November 2017

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## For every non-leaf node ''n'', assign the number of registers needed to evaluate the respective subtrees of ''n''. If the number of registers needed in the left subtree (''l'') are not equal to the number of registers needed in the right subtree (''r''), the number of registers needed for the current node ''n'' is max(l, r). If ''l == r'', then the number of registers needed for the current node is ''r'' + 1.

# Code emission

## If the number of registers needed to compute the left subtree of node ''n'' is bigger than the number of registers for the right subtree, then the left subtree is evaluated first (since it may be possible that the one more register needed by the leftright subtree to save the result makes the rightleft subtree [[Register spilling|spill]]). If the right subtree needs more registers than the left subtree, the right subtree is evaluated first accordingly. If both subtrees need equal as much registers, then the order of evaluation is irrelevant.

===Example===