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If there is only a single available value, all uses must be dominated by
the single value and there is no need to search for a reaching
definition.
This drastically speeds up LCSSA in some cases. For the test case
from PR37202, it speeds up LCSSA construction by 4 times.
Time-passes without this patch for test case from PR37202:
Total Execution Time: 29.9285 seconds (29.9276 wall clock)
---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
5.2786 ( 17.7%) 0.0021 ( 1.2%) 5.2806 ( 17.6%) 5.2808 ( 17.6%) Unswitch loops
4.3739 ( 14.7%) 0.0303 ( 18.1%) 4.4042 ( 14.7%) 4.4042 ( 14.7%) Loop-Closed SSA Form Pass
4.2658 ( 14.3%) 0.0192 ( 11.5%) 4.2850 ( 14.3%) 4.2851 ( 14.3%) Loop-Closed SSA Form Pass #2
2.2307 ( 7.5%) 0.0013 ( 0.8%) 2.2320 ( 7.5%) 2.2318 ( 7.5%) Loop Invariant Code Motion
2.0888 ( 7.0%) 0.0012 ( 0.7%) 2.0900 ( 7.0%) 2.0897 ( 7.0%) Unroll loops
1.6761 ( 5.6%) 0.0013 ( 0.8%) 1.6774 ( 5.6%) 1.6774 ( 5.6%) Value Propagation
1.3686 ( 4.6%) 0.0029 ( 1.8%) 1.3716 ( 4.6%) 1.3714 ( 4.6%) Induction Variable Simplification
1.1457 ( 3.8%) 0.0010 ( 0.6%) 1.1468 ( 3.8%) 1.1468 ( 3.8%) Loop-Closed SSA Form Pass #4
1.1384 ( 3.8%) 0.0005 ( 0.3%) 1.1389 ( 3.8%) 1.1389 ( 3.8%) Loop-Closed SSA Form Pass #6
1.1360 ( 3.8%) 0.0027 ( 1.6%) 1.1387 ( 3.8%) 1.1387 ( 3.8%) Loop-Closed SSA Form Pass #5
1.1331 ( 3.8%) 0.0010 ( 0.6%) 1.1341 ( 3.8%) 1.1340 ( 3.8%) Loop-Closed SSA Form Pass #3
Time passes with this patch
Total Execution Time: 19.2802 seconds (19.2813 wall clock)
---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
4.4234 ( 23.2%) 0.0038 ( 2.0%) 4.4272 ( 23.0%) 4.4273 ( 23.0%) Unswitch loops
2.3828 ( 12.5%) 0.0020 ( 1.1%) 2.3848 ( 12.4%) 2.3847 ( 12.4%) Unroll loops
1.8714 ( 9.8%) 0.0020 ( 1.1%) 1.8734 ( 9.7%) 1.8735 ( 9.7%) Loop Invariant Code Motion
1.7973 ( 9.4%) 0.0022 ( 1.2%) 1.7995 ( 9.3%) 1.8003 ( 9.3%) Value Propagation
1.4010 ( 7.3%) 0.0033 ( 1.8%) 1.4043 ( 7.3%) 1.4044 ( 7.3%) Induction Variable Simplification
0.9978 ( 5.2%) 0.0244 ( 13.1%) 1.0222 ( 5.3%) 1.0224 ( 5.3%) Loop-Closed SSA Form Pass #2
0.9611 ( 5.0%) 0.0257 ( 13.8%) 0.9868 ( 5.1%) 0.9868 ( 5.1%) Loop-Closed SSA Form Pass
0.5856 ( 3.1%) 0.0015 ( 0.8%) 0.5871 ( 3.0%) 0.5869 ( 3.0%) Unroll loops #2
0.4132 ( 2.2%) 0.0012 ( 0.7%) 0.4145 ( 2.1%) 0.4143 ( 2.1%) Loop Invariant Code Motion #3
Reviewers: efriedma, davide, mzolotukhin
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D57033
llvm-svn: 352960
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Summary:
Extend LCSSA so that debug values outside loops are rewritten to
use the PHI nodes that the pass creates.
This fixes PR39019. In that case, we ran LCSSA on a loop that
was later on vectorized, which left us with something like this:
for.cond.cleanup:
%add.lcssa = phi i32 [ %add, %for.body ], [ %34, %middle.block ]
call void @llvm.dbg.value(metadata i32 %add,
ret i32 %add.lcssa
for.body:
%add =
[...]
br i1 %exitcond, label %for.cond.cleanup, label %for.body
which later resulted in the debug.value becoming undef when
removing the scalar loop (and the location would have probably
been wrong for the vectorized case otherwise).
As we now may need to query the AvailableVals cache more than
once for a basic block, FindAvailableVals() in SSAUpdaterImpl is
changed so that it updates the cache for blocks that we do not
create a PHI node for, regardless of the block's number of
predecessors. The debug value in the attached IR reproducer
would not be properly rewritten without this.
Debug values residing in blocks where we have not inserted any
PHI nodes are currently left as-is by this patch. I'm not sure
what should be done with those uses.
Reviewers: mattd, aprantl, vsk, probinson
Reviewed By: mattd, aprantl
Subscribers: jmorse, gbedwell, JDevlieghere, llvm-commits
Differential Revision: https://reviews.llvm.org/D53130
llvm-svn: 344589
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