------- Additional Comments From kazu at cs dot umass dot edu 2005-02-06 17:49
-------
Hi Richard,
I didn't say that load elimination is the *only* way to take this
optimization opportunity.
DOM *can* thread incoming edges to a basic block with more than COND_EXPR
or SWITCH_EXPR in limited circumstances.
One problem here is that upon taking edge from <bb 0> to <L1>,
DOM does not record that D.1317_2 == 0.
Once we fix that, then D.1317_4 = *flag_1; is folded to D.1317_4 = 0;,
but DOM wants to see an SSA_NAME on rhs on every MODIFY_EXPR leading up to
COND_EXPR or SWITCH_EXPR.
If DOM also knew that D.1317_2 == D.1317_4, it could thread the edge in
question, but I cannot think of an easy way of teaching DOM how to
figure out equivalences of two SSA_NAMEs when we already have a known constant
value.
CCing Jeff as he is the DOM person.
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What |Removed |Added
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CC| |law at redhat dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19516
