[llvm] [HashRecognize] Make it a non-PM analysis (PR #144742)
Ramkumar Ramachandra via llvm-commits
llvm-commits at lists.llvm.org
Wed Jun 18 13:00:50 PDT 2025
https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/144742
>From b7ce77875982ae4d3c392f8bdb827818dd8dd390 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Wed, 18 Jun 2025 16:56:05 +0100
Subject: [PATCH] [HashRecognize] Fix the analysis result
Make the analysis return a proper analysis result that can be cached,
instead of a HashRecognize object which has to be called to perform the
actual analysis. This also means that we need a function_ref to generate
the Sarwate table returned along with the analysis result. The issue was
discovered when attempting to use the analysis to perform a transform.
---
llvm/include/llvm/Analysis/HashRecognize.h | 21 +++++---------
llvm/lib/Analysis/HashRecognize.cpp | 33 +++++++++++-----------
llvm/lib/Passes/PassRegistry.def | 1 -
3 files changed, 24 insertions(+), 31 deletions(-)
diff --git a/llvm/include/llvm/Analysis/HashRecognize.h b/llvm/include/llvm/Analysis/HashRecognize.h
index c169383bf7b08..970b4398a68c9 100644
--- a/llvm/include/llvm/Analysis/HashRecognize.h
+++ b/llvm/include/llvm/Analysis/HashRecognize.h
@@ -66,6 +66,10 @@ struct PolynomialInfo {
// Set to true in the case of big-endian.
bool ByteOrderSwapped;
+ // A function_ref to generate the Sarwate lookup-table, which can be used to
+ // optimize CRC in the absence of target-specific instructions.
+ function_ref<CRCTable(const APInt &, bool)> GenSarwateTable;
+
// An optional auxiliary checksum that augments the LHS. In the case of CRC,
// it is XOR'ed with the LHS, so that the computation's final remainder is
// zero.
@@ -73,6 +77,7 @@ struct PolynomialInfo {
PolynomialInfo(unsigned TripCount, Value *LHS, const APInt &RHS,
Value *ComputedValue, bool ByteOrderSwapped,
+ function_ref<CRCTable(const APInt &, bool)> GenSarwateTable,
Value *LHSAux = nullptr);
};
@@ -84,12 +89,9 @@ class HashRecognize {
public:
HashRecognize(const Loop &L, ScalarEvolution &SE);
- // The main analysis entry point.
+ // The main analysis entry points.
std::variant<PolynomialInfo, ErrBits, StringRef> recognizeCRC() const;
-
- // Auxilary entry point after analysis to interleave the generating polynomial
- // and return a 256-entry CRC table.
- CRCTable genSarwateTable(const APInt &GenPoly, bool ByteOrderSwapped) const;
+ std::optional<PolynomialInfo> getResult() const;
void print(raw_ostream &OS) const;
@@ -107,15 +109,6 @@ class HashRecognizePrinterPass
PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR, LPMUpdater &);
};
-
-class HashRecognizeAnalysis : public AnalysisInfoMixin<HashRecognizeAnalysis> {
- friend AnalysisInfoMixin<HashRecognizeAnalysis>;
- static AnalysisKey Key;
-
-public:
- using Result = HashRecognize;
- Result run(Loop &L, LoopAnalysisManager &AM, LoopStandardAnalysisResults &AR);
-};
} // namespace llvm
#endif
diff --git a/llvm/lib/Analysis/HashRecognize.cpp b/llvm/lib/Analysis/HashRecognize.cpp
index d11602f921872..850b6be412d16 100644
--- a/llvm/lib/Analysis/HashRecognize.cpp
+++ b/llvm/lib/Analysis/HashRecognize.cpp
@@ -442,11 +442,13 @@ getRecurrences(BasicBlock *LoopLatch, const PHINode *IndVar, const Loop &L) {
return std::make_pair(SimpleRecurrence, ConditionalRecurrence);
}
-PolynomialInfo::PolynomialInfo(unsigned TripCount, Value *LHS, const APInt &RHS,
- Value *ComputedValue, bool ByteOrderSwapped,
- Value *LHSAux)
+PolynomialInfo::PolynomialInfo(
+ unsigned TripCount, Value *LHS, const APInt &RHS, Value *ComputedValue,
+ bool ByteOrderSwapped,
+ function_ref<CRCTable(const APInt &, bool)> GenSarwateTable, Value *LHSAux)
: TripCount(TripCount), LHS(LHS), RHS(RHS), ComputedValue(ComputedValue),
- ByteOrderSwapped(ByteOrderSwapped), LHSAux(LHSAux) {}
+ ByteOrderSwapped(ByteOrderSwapped), GenSarwateTable(GenSarwateTable),
+ LHSAux(LHSAux) {}
/// In the big-endian case, checks the bottom N bits against CheckFn, and that
/// the rest are unknown. In the little-endian case, checks the top N bits
@@ -471,8 +473,7 @@ static bool checkExtractBits(const KnownBits &Known, unsigned N,
/// Generate a lookup table of 256 entries by interleaving the generating
/// polynomial. The optimization technique of table-lookup for CRC is also
/// called the Sarwate algorithm.
-CRCTable HashRecognize::genSarwateTable(const APInt &GenPoly,
- bool ByteOrderSwapped) const {
+static CRCTable genSarwateTable(const APInt &GenPoly, bool ByteOrderSwapped) {
unsigned BW = GenPoly.getBitWidth();
CRCTable Table;
Table[0] = APInt::getZero(BW);
@@ -625,7 +626,7 @@ HashRecognize::recognizeCRC() const {
Value *LHSAux = SimpleRecurrence ? SimpleRecurrence.Start : nullptr;
return PolynomialInfo(TC, ConditionalRecurrence.Start, GenPoly, ComputedValue,
- *ByteOrderSwapped, LHSAux);
+ *ByteOrderSwapped, genSarwateTable, LHSAux);
}
void CRCTable::print(raw_ostream &OS) const {
@@ -679,13 +680,20 @@ void HashRecognize::print(raw_ostream &OS) const {
OS << "\n";
}
OS.indent(2) << "Computed CRC lookup table:\n";
- genSarwateTable(Info.RHS, Info.ByteOrderSwapped).print(OS);
+ Info.GenSarwateTable(Info.RHS, Info.ByteOrderSwapped).print(OS);
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void HashRecognize::dump() const { print(dbgs()); }
#endif
+std::optional<PolynomialInfo> HashRecognize::getResult() const {
+ auto Res = HashRecognize(L, SE).recognizeCRC();
+ if (std::holds_alternative<PolynomialInfo>(Res))
+ return std::get<PolynomialInfo>(Res);
+ return std::nullopt;
+}
+
HashRecognize::HashRecognize(const Loop &L, ScalarEvolution &SE)
: L(L), SE(SE) {}
@@ -693,13 +701,6 @@ PreservedAnalyses HashRecognizePrinterPass::run(Loop &L,
LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR,
LPMUpdater &) {
- AM.getResult<HashRecognizeAnalysis>(L, AR).print(OS);
+ HashRecognize(L, AR.SE).print(OS);
return PreservedAnalyses::all();
}
-
-HashRecognize HashRecognizeAnalysis::run(Loop &L, LoopAnalysisManager &AM,
- LoopStandardAnalysisResults &AR) {
- return {L, AR.SE};
-}
-
-AnalysisKey HashRecognizeAnalysis::Key;
diff --git a/llvm/lib/Passes/PassRegistry.def b/llvm/lib/Passes/PassRegistry.def
index f761d0dab09a8..ec14c6a9211d9 100644
--- a/llvm/lib/Passes/PassRegistry.def
+++ b/llvm/lib/Passes/PassRegistry.def
@@ -672,7 +672,6 @@ LOOPNEST_PASS("no-op-loopnest", NoOpLoopNestPass())
#define LOOP_ANALYSIS(NAME, CREATE_PASS)
#endif
LOOP_ANALYSIS("ddg", DDGAnalysis())
-LOOP_ANALYSIS("hash-recognize", HashRecognizeAnalysis())
LOOP_ANALYSIS("iv-users", IVUsersAnalysis())
LOOP_ANALYSIS("no-op-loop", NoOpLoopAnalysis())
LOOP_ANALYSIS("pass-instrumentation", PassInstrumentationAnalysis(PIC))
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