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[SCEV] Avoid repeated proveNoSignedWrapViaInduction calls. 

At the moment, proveNoSignedWrapViaInduction may be called for the
same AddRec a large number of times via getSignExtendExpr. This can have
a severe compile-time impact for very loop-heavy code.

If proveNoSignedWrapViaInduction failed to prove NSW the first time,
it is unlikely to succeed on subsequent tries and the cost doesn't seem
to be justified.

This is the signed version of 8daa338297 / D130648.

This can drastically improve compile-time in some excessive cases and
also has a slightly positive compile-time impact on CTMark:

NewPM-O3: -0.06%
NewPM-ReleaseThinLTO: -0.04%
NewPM-ReleaseLTO-g: -0.04%

https://llvm-compile-time-tracker.com/compare.php?from=8daa338297d533db4d1ae8d3770613eb25c29688&to=aed126a196e7a5a9803543d9b4d6bdb233d0009c&stat=instructions

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D130694
This commit is contained in:
Florian Hahn 2022-07-29 09:15:02 +01:00
parent 0595edd80f
commit 214e2d8fe5
No known key found for this signature in database
GPG Key ID: EEF712BB5E80EBBA
2 changed files with 11 additions and 1 deletions
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4
llvm/include/llvm/Analysis/ScalarEvolution.h
View File

@ -2119,6 +2119,10 @@ private:
/// tried.
SmallPtrSet<const SCEVAddRecExpr *, 16> UnsignedWrapViaInductionTried;
/// Set of AddRecs for which proving NSW via an induction has already been
/// tried.
SmallPtrSet<const SCEVAddRecExpr *, 16> SignedWrapViaInductionTried;
/// The head of a linked list of all SCEVUnknown values that have been
/// allocated. This is used by releaseMemory to locate them all and call
/// their destructors.

8
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -4958,6 +4958,10 @@ ScalarEvolution::proveNoSignedWrapViaInduction(const SCEVAddRecExpr *AR) {
if (!AR->isAffine())
return Result;
// This function can be expensive, only try to prove NSW once per AddRec.
if (!SignedWrapViaInductionTried.insert(AR).second)
return Result;
const SCEV *Step = AR->getStepRecurrence(*this);
const Loop *L = AR->getLoop();
@ -13584,8 +13588,10 @@ void ScalarEvolution::forgetMemoizedResultsImpl(const SCEV *S) {
HasRecMap.erase(S);
MinTrailingZerosCache.erase(S);
if (auto *AR = dyn_cast<SCEVAddRecExpr>(S))
if (auto *AR = dyn_cast<SCEVAddRecExpr>(S)) {
UnsignedWrapViaInductionTried.erase(AR);
SignedWrapViaInductionTried.erase(AR);
}
auto ExprIt = ExprValueMap.find(S);
if (ExprIt != ExprValueMap.end()) {