Factor out the reachability such that multiple queries to find reachability of values are fast. This is based on finding
the ANTIC points
in the CFG which do not change during hoisting. The ANTIC points are basically the dominance-frontiers in the inverse
graph. So we introduce a data structure (CHI nodes)
to keep track of values flowing out of a basic block. We only do this for values with multiple occurrences in the
function as they are the potential hoistable candidates.
This patch allows us to hoist instructions to a basic block with >2 successors, as well as deal with infinite loops in a
trivial way.
Relevant test cases are added to show the functionality as well as regression fixes from PR32821.
Regression from previous GVNHoist:
We do not hoist fully redundant expressions because fully redundant expressions are already handled by NewGVN
Differential Revision: https://reviews.llvm.org/D35918
Reviewers: dberlin, sebpop, gberry,
llvm-svn: 313116
Without this patch, GVN-hoist would think that a branch instruction is a scalar instruction
and would try to value number it. The patch filters out all such kind of irrelevant instructions.
A bit frustrating is that there is no easy way to discard all those very infrequent instructions,
a bit like isa<TerminatorInst> that stands for a large family of instructions. I'm thinking that
checking for those very infrequent other instructions would cost us more in compilation time
than just letting those instructions getting numbered, so I'm still thinking that a simpler check:
if (isa<TerminatorInst>(I))
return false;
is better than listing all the other less frequent instructions.
Differential Revision: https://reviews.llvm.org/D23929
llvm-svn: 282160
Aditya Kumar