http://llvm.org/bugs/show_bug.cgi?id=2495
Summary: Dominator queries should be lazy
Product: libraries
Version: trunk
Platform: PC
OS/Version: All
Status: NEW
Keywords: slow-compile
Severity: normal
Priority: P2
Component: Global Analyses
AssignedTo: [EMAIL PROTECTED]
ReportedBy: [EMAIL PROTECTED]
CC: [email protected]
llvm-ld runs mem2reg after jump threading because jump threading introduces
allocas in some cases. However, the number of cases it does this is pretty
low.
Because mem2reg is run after jump threading, the pass manager computes
dominator info and dom frontier info. However, if there are no promotable
allocas in the function this information is just thrown away again and never
used.
We should make domfrontier and domtree be lazy: compute their info for the
function on the first meaningful query, instead of computing everything in
runOnFunction.
One minor issue with this is that the time to compute this dom info will be
charged (in -time-passes) to the pass that uses it, instead of to the analysis
pass. You could argue that this is actually a good thing though.
-Chris
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