[SLP] Increase UsesLimit to 64 #99467
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Since commit 82b800e addressed the issue llvm#99327 , we see some performance regression (13%) on some verilator generated C++ code. This is because the UsesLimit is set to 8, which is too small for the verilator generated code. I have analyzed the need for the UsesLimit from [1] and found that the UsesLimit should be at least 64 to cover most of these cases. Thus, This patch increases the UsesLimit to 64. Link: llvm#99327 (comment) [1] Signed-off-by: Yangyu Chen <[email protected]>
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@llvm/pr-subscribers-llvm-transforms Author: Yangyu Chen (cyyself) ChangesSince commit 82b800e addressed the issue #99327 , we see some performance regression (13%) on some verilator generated C++ code. This is because the UsesLimit is set to 8, which is too small for the verilator generated code. I have analyzed the need for the UsesLimit from [1] and found that the UsesLimit should be at least 64 to cover most of these cases. Thus, This patch increases the UsesLimit to 64. Link: #99327 (comment) [1] Full diff: https://github.com/llvm/llvm-project/pull/99467.diff 1 Files Affected:
diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index d88c6307b994b..6f0878d5384be 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -209,7 +209,7 @@ static const unsigned AliasedCheckLimit = 10;
// Limit of the number of uses for potentially transformed instructions/values,
// used in checks to avoid compile-time explode.
-static constexpr int UsesLimit = 8;
+static constexpr int UsesLimit = 64;
// Another limit for the alias checks: The maximum distance between load/store
// instructions where alias checks are done.
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I've created a branch (perf/slp_usecase_limit) to determine the effect on compile time - it should appear on https://llvm-compile-time-tracker.com/?config=Overview&stat=instructions%3Au&remote=RKSimon in the next hour |
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Yeah. Surprisingly it also improves the performance of clang stage2-build. |
Most probably, it has lots of uses, which must be replaced by the new extractelement instructions. And if the number is >8 but <64, better to walk over actual uses, rather than all uses (including those, potentially deleted/dropped a bit later) |
Since commit 82b800e addressed the issue #99327 , we see some performance regression (13%) on some verilator generated C++ code. This is because the UsesLimit is set to 8, which is too small for the verilator generated code. I have analyzed the need for the UsesLimit from [1] and found that the UsesLimit should be at least 64 to cover most of these cases. Thus, This patch increases the UsesLimit to 64. Link: #99327 (comment) [1] Signed-off-by: Yangyu Chen <[email protected]>
Since commit 82b800e addressed the issue #99327 , we see some performance regression (13%) on some verilator generated C++ code. This is because the UsesLimit is set to 8, which is too small for the verilator generated code. I have analyzed the need for the UsesLimit from [1] and found that the UsesLimit should be at least 64 to cover most of these cases. Thus, This patch increases the UsesLimit to 64.
Link: #99327 (comment) [1]