// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
-//
-// This file implements a simple interprocedural pass which walks the
-// call-graph, looking for functions which do not access or only read
-// non-local memory, and marking them readnone/readonly. It does the
-// same with function arguments independently, marking them readonly/
-// readnone/nocapture. Finally, well-known library call declarations
-// are marked with all attributes that are consistent with the
-// function's standard definition. This pass is implemented as a
-// bottom-up traversal of the call-graph.
-//
+///
+/// \file
+/// This file implements interprocedural passes which walk the
+/// call-graph deducing and/or propagating function attributes.
+///
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO.h"
}
namespace {
-struct FunctionAttrs : public CallGraphSCCPass {
+struct PostOrderFunctionAttrs : public CallGraphSCCPass {
static char ID; // Pass identification, replacement for typeid
- FunctionAttrs() : CallGraphSCCPass(ID) {
- initializeFunctionAttrsPass(*PassRegistry::getPassRegistry());
+ PostOrderFunctionAttrs() : CallGraphSCCPass(ID) {
+ initializePostOrderFunctionAttrsPass(*PassRegistry::getPassRegistry());
}
bool runOnSCC(CallGraphSCC &SCC) override;
- bool doInitialization(CallGraph &CG) override {
- Revisit.clear();
- return false;
- }
- bool doFinalization(CallGraph &CG) override;
-
+
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<AssumptionCacheTracker>();
private:
TargetLibraryInfo *TLI;
- SmallVector<WeakVH,16> Revisit;
};
}
-char FunctionAttrs::ID = 0;
-INITIALIZE_PASS_BEGIN(FunctionAttrs, "functionattrs",
+char PostOrderFunctionAttrs::ID = 0;
+INITIALIZE_PASS_BEGIN(PostOrderFunctionAttrs, "functionattrs",
"Deduce function attributes", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
-INITIALIZE_PASS_END(FunctionAttrs, "functionattrs",
+INITIALIZE_PASS_END(PostOrderFunctionAttrs, "functionattrs",
"Deduce function attributes", false, false)
-Pass *llvm::createFunctionAttrsPass() { return new FunctionAttrs(); }
+Pass *llvm::createPostOrderFunctionAttrsPass() { return new PostOrderFunctionAttrs(); }
namespace {
/// The three kinds of memory access relevant to 'readonly' and
return true;
}
-static bool addNoRecurseAttrs(const CallGraphSCC &SCC,
- SmallVectorImpl<WeakVH> &Revisit) {
+static bool addNoRecurseAttrs(const CallGraphSCC &SCC) {
// Try and identify functions that do not recurse.
// If the SCC contains multiple nodes we know for sure there is recursion.
// Function calls a potentially recursive function.
return setDoesNotRecurse(*F);
- // We know that F is not obviously recursive, but we haven't been able to
- // prove that it doesn't actually recurse. Add it to the Revisit list to try
- // again top-down later.
- Revisit.push_back(F);
+ // Nothing else we can deduce usefully during the postorder traversal.
return false;
}
-static bool addNoRecurseAttrsTopDownOnly(Function *F) {
- // If F is internal and all uses are in norecurse functions, then F is also
- // norecurse.
- if (F->doesNotRecurse())
- return false;
- if (F->hasInternalLinkage()) {
- for (auto *U : F->users())
- if (auto *I = dyn_cast<Instruction>(U)) {
- if (!I->getParent()->getParent()->doesNotRecurse())
- return false;
- } else {
- return false;
- }
- return setDoesNotRecurse(*F);
- }
- return false;
-}
-
-bool FunctionAttrs::runOnSCC(CallGraphSCC &SCC) {
+bool PostOrderFunctionAttrs::runOnSCC(CallGraphSCC &SCC) {
TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
bool Changed = false;
Changed |= addNoAliasAttrs(SCCNodes);
Changed |= addNonNullAttrs(SCCNodes, *TLI);
}
-
- Changed |= addNoRecurseAttrs(SCC, Revisit);
+
+ Changed |= addNoRecurseAttrs(SCC);
return Changed;
}
-bool FunctionAttrs::doFinalization(CallGraph &CG) {
+namespace {
+/// A pass to do RPO deduction and propagation of function attributes.
+///
+/// This pass provides a general RPO or "top down" propagation of
+/// function attributes. For a few (rare) cases, we can deduce significantly
+/// more about function attributes by working in RPO, so this pass
+/// provides the compliment to the post-order pass above where the majority of
+/// deduction is performed.
+// FIXME: Currently there is no RPO CGSCC pass structure to slide into and so
+// this is a boring module pass, but eventually it should be an RPO CGSCC pass
+// when such infrastructure is available.
+struct ReversePostOrderFunctionAttrs : public ModulePass {
+ static char ID; // Pass identification, replacement for typeid
+ ReversePostOrderFunctionAttrs() : ModulePass(ID) {
+ initializeReversePostOrderFunctionAttrsPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnModule(Module &M) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.setPreservesCFG();
+ AU.addRequired<CallGraphWrapperPass>();
+ }
+};
+}
+
+char ReversePostOrderFunctionAttrs::ID = 0;
+INITIALIZE_PASS_BEGIN(ReversePostOrderFunctionAttrs, "rpo-functionattrs",
+ "Deduce function attributes in RPO", false, false)
+INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
+INITIALIZE_PASS_END(ReversePostOrderFunctionAttrs, "rpo-functionattrs",
+ "Deduce function attributes in RPO", false, false)
+
+Pass *llvm::createReversePostOrderFunctionAttrsPass() {
+ return new ReversePostOrderFunctionAttrs();
+}
+
+static bool addNoRecurseAttrsTopDown(Function &F) {
+ // We check the preconditions for the function prior to calling this to avoid
+ // the cost of building up a reversible post-order list. We assert them here
+ // to make sure none of the invariants this relies on were violated.
+ assert(!F.isDeclaration() && "Cannot deduce norecurse without a definition!");
+ assert(!F.doesNotRecurse() &&
+ "This function has already been deduced as norecurs!");
+ assert(F.hasInternalLinkage() &&
+ "Can only do top-down deduction for internal linkage functions!");
+
+ // If F is internal and all of its uses are calls from a non-recursive
+ // functions, then none of its calls could in fact recurse without going
+ // through a function marked norecurse, and so we can mark this function too
+ // as norecurse. Note that the uses must actually be calls -- otherwise
+ // a pointer to this function could be returned from a norecurse function but
+ // this function could be recursively (indirectly) called. Note that this
+ // also detects if F is directly recursive as F is not yet marked as
+ // a norecurse function.
+ for (auto *U : F.users()) {
+ auto *I = dyn_cast<Instruction>(U);
+ if (!I)
+ return false;
+ CallSite CS(I);
+ if (!CS || !CS.getParent()->getParent()->doesNotRecurse())
+ return false;
+ }
+ return setDoesNotRecurse(F);
+}
+
+bool ReversePostOrderFunctionAttrs::runOnModule(Module &M) {
+ // We only have a post-order SCC traversal (because SCCs are inherently
+ // discovered in post-order), so we accumulate them in a vector and then walk
+ // it in reverse. This is simpler than using the RPO iterator infrastructure
+ // because we need to combine SCC detection and the PO walk of the call
+ // graph. We can also cheat egregiously because we're primarily interested in
+ // synthesizing norecurse and so we can only save the singular SCCs as SCCs
+ // with multiple functions in them will clearly be recursive.
+ auto &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
+ SmallVector<Function *, 16> Worklist;
+ for (scc_iterator<CallGraph *> I = scc_begin(&CG); !I.isAtEnd(); ++I) {
+ if (I->size() != 1)
+ continue;
+
+ Function *F = I->front()->getFunction();
+ if (F && !F->isDeclaration() && !F->doesNotRecurse() &&
+ F->hasInternalLinkage())
+ Worklist.push_back(F);
+ }
+
bool Changed = false;
- // When iterating over SCCs we visit functions in a bottom-up fashion. Some of
- // the rules we have for identifying norecurse functions work best with a
- // top-down walk, so look again at all the functions we previously marked as
- // worth revisiting, in top-down order.
- for (auto &F : reverse(Revisit))
- if (F)
- Changed |= addNoRecurseAttrsTopDownOnly(cast<Function>((Value*)F));
+ for (auto *F : reverse(Worklist))
+ Changed |= addNoRecurseAttrsTopDown(*F);
+
return Changed;
}
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