[llvm] r251640 - [FunctionAttrs] Provide a single SCC node set to all of the
Philip Reames via llvm-commits
llvm-commits at lists.llvm.org
Tue Nov 3 18:15:33 PST 2015
Chandler,
I noticed the handling in this change for ExternalNode. I *think* that
the code in question is only unnecessarily conservative for non-null and
no alias inference, but is incorrect for readonly, readnone, and
argument attributes.
In particular, none of these analyzes should be able to make any
speculative conclusions about an SCC which contains an external call.
By filtering the external node out of the SCC, I think you've allowed
them to do so. Am I wrong here?
Philip
On 10/29/2015 11:29 AM, Chandler Carruth via llvm-commits wrote:
> Author: chandlerc
> Date: Thu Oct 29 13:29:15 2015
> New Revision: 251640
>
> URL: http://llvm.org/viewvc/llvm-project?rev=251640&view=rev
> Log:
> [FunctionAttrs] Provide a single SCC node set to all of the
> transformations in FunctionAttrs rather than building a new one each
> time.
>
> This isn't trivial because there are different heuristics from different
> passes for exactly what set they want. The primary difference is whether
> an *overridable* function completely disables the synthesis of
> attributes. I've modeled this by directly testing for overridable, and
> using the common set that excludes external and opt-none functions.
>
> This does cause some changes by disabling more optimizations in the face
> of opt-none. Specifically, we were still optimizing *calls* to opt-none
> functions based on their attributes, just not the bodies. It seems
> better to be conservative on both fronts given the intended semanticas
> here (best effort to not assume or disturb anything). I've not tried to
> test this change as it seems complex, brittle, and not important to the
> implicit contract of opt-none. Instead, it seems more like a choice that
> should be dictated by the simplified implementation and the change to be
> acceptable differences within the space of opt-none.
>
> A big benefit here is that these transformations no longer rely on the
> legacy pass manager's SCC types, they just work on generic sets of
> function pointers. This will make it easy to re-use their logic in the
> new pass manager.
>
> I've also made the transforms static functions instead of members where
> trivial while I was touching the signatures.
>
> Modified:
> llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp
>
> Modified: llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp?rev=251640&r1=251639&r2=251640&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp (original)
> +++ llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp Thu Oct 29 13:29:15 2015
> @@ -52,6 +52,10 @@ STATISTIC(NumNonNullReturn, "Number of f
> STATISTIC(NumAnnotated, "Number of attributes added to library functions");
>
> namespace {
> +typedef SmallSetVector<Function *, 8> SCCNodeSet;
> +}
> +
> +namespace {
> struct FunctionAttrs : public CallGraphSCCPass {
> static char ID; // Pass identification, replacement for typeid
> FunctionAttrs() : CallGraphSCCPass(ID) {
> @@ -70,10 +74,7 @@ struct FunctionAttrs : public CallGraphS
> private:
> TargetLibraryInfo *TLI;
>
> - bool AddReadAttrs(const CallGraphSCC &SCC);
> - bool AddArgumentAttrs(const CallGraphSCC &SCC);
> - bool AddNoAliasAttrs(const CallGraphSCC &SCC);
> - bool AddNonNullAttrs(const CallGraphSCC &SCC);
> + bool AddReadAttrs(const SCCNodeSet &SCCNodes);
> bool annotateLibraryCalls(const CallGraphSCC &SCC);
> };
> }
> @@ -99,9 +100,8 @@ enum MemoryAccessKind {
> };
> }
>
> -static MemoryAccessKind
> -checkFunctionMemoryAccess(Function &F, AAResults &AAR,
> - const SmallPtrSetImpl<Function *> &SCCNodes) {
> +static MemoryAccessKind checkFunctionMemoryAccess(Function &F, AAResults &AAR,
> + const SCCNodeSet &SCCNodes) {
> FunctionModRefBehavior MRB = AAR.getModRefBehavior(&F);
> if (MRB == FMRB_DoesNotAccessMemory)
> // Already perfect!
> @@ -205,25 +205,11 @@ checkFunctionMemoryAccess(Function &F, A
> }
>
> /// Deduce readonly/readnone attributes for the SCC.
> -bool FunctionAttrs::AddReadAttrs(const CallGraphSCC &SCC) {
> - SmallPtrSet<Function *, 8> SCCNodes;
> -
> - // Fill SCCNodes with the elements of the SCC. Used for quickly
> - // looking up whether a given CallGraphNode is in this SCC.
> - for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
> - SCCNodes.insert((*I)->getFunction());
> -
> +bool FunctionAttrs::AddReadAttrs(const SCCNodeSet &SCCNodes) {
> // Check if any of the functions in the SCC read or write memory. If they
> // write memory then they can't be marked readnone or readonly.
> bool ReadsMemory = false;
> - for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
> - Function *F = (*I)->getFunction();
> -
> - if (!F || F->hasFnAttribute(Attribute::OptimizeNone))
> - // External node or node we don't want to optimize - assume it may write
> - // memory and give up.
> - return false;
> -
> + for (Function *F : SCCNodes) {
> // We need to manually construct BasicAA directly in order to disable its
> // use of other function analyses.
> BasicAAResult BAR(createLegacyPMBasicAAResult(*this, *F));
> @@ -247,9 +233,7 @@ bool FunctionAttrs::AddReadAttrs(const C
> // Success! Functions in this SCC do not access memory, or only read memory.
> // Give them the appropriate attribute.
> bool MadeChange = false;
> - for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
> - Function *F = (*I)->getFunction();
> -
> + for (Function *F : SCCNodes) {
> if (F->doesNotAccessMemory())
> // Already perfect!
> continue;
> @@ -325,7 +309,7 @@ public:
> /// consider that a capture, instead adding it to the "Uses" list and
> /// continuing with the analysis.
> struct ArgumentUsesTracker : public CaptureTracker {
> - ArgumentUsesTracker(const SmallPtrSet<Function *, 8> &SCCNodes)
> + ArgumentUsesTracker(const SCCNodeSet &SCCNodes)
> : Captured(false), SCCNodes(SCCNodes) {}
>
> void tooManyUses() override { Captured = true; }
> @@ -338,7 +322,8 @@ struct ArgumentUsesTracker : public Capt
> }
>
> Function *F = CS.getCalledFunction();
> - if (!F || !SCCNodes.count(F)) {
> + if (!F || F->isDeclaration() || F->mayBeOverridden() ||
> + !SCCNodes.count(F)) {
> Captured = true;
> return true;
> }
> @@ -366,7 +351,7 @@ struct ArgumentUsesTracker : public Capt
> bool Captured; // True only if certainly captured (used outside our SCC).
> SmallVector<Argument *, 4> Uses; // Uses within our SCC.
>
> - const SmallPtrSet<Function *, 8> &SCCNodes;
> + const SCCNodeSet &SCCNodes;
> };
> }
>
> @@ -501,20 +486,9 @@ determinePointerReadAttrs(Argument *A,
> }
>
> /// Deduce nocapture attributes for the SCC.
> -bool FunctionAttrs::AddArgumentAttrs(const CallGraphSCC &SCC) {
> +static bool addArgumentAttrs(const SCCNodeSet &SCCNodes) {
> bool Changed = false;
>
> - SmallPtrSet<Function *, 8> SCCNodes;
> -
> - // Fill SCCNodes with the elements of the SCC. Used for quickly
> - // looking up whether a given CallGraphNode is in this SCC.
> - for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
> - Function *F = (*I)->getFunction();
> - if (F && !F->isDeclaration() && !F->mayBeOverridden() &&
> - !F->hasFnAttribute(Attribute::OptimizeNone))
> - SCCNodes.insert(F);
> - }
> -
> ArgumentGraph AG;
>
> AttrBuilder B;
> @@ -522,14 +496,7 @@ bool FunctionAttrs::AddArgumentAttrs(con
>
> // Check each function in turn, determining which pointer arguments are not
> // captured.
> - for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
> - Function *F = (*I)->getFunction();
> -
> - if (!F || F->hasFnAttribute(Attribute::OptimizeNone))
> - // External node or function we're trying not to optimize - only a problem
> - // for arguments that we pass to it.
> - continue;
> -
> + for (Function *F : SCCNodes) {
> // Definitions with weak linkage may be overridden at linktime with
> // something that captures pointers, so treat them like declarations.
> if (F->isDeclaration() || F->mayBeOverridden())
> @@ -714,8 +681,7 @@ bool FunctionAttrs::AddArgumentAttrs(con
> ///
> /// A function is "malloc-like" if it returns either null or a pointer that
> /// doesn't alias any other pointer visible to the caller.
> -static bool isFunctionMallocLike(Function *F,
> - SmallPtrSet<Function *, 8> &SCCNodes) {
> +static bool isFunctionMallocLike(Function *F, const SCCNodeSet &SCCNodes) {
> SmallSetVector<Value *, 8> FlowsToReturn;
> for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
> if (ReturnInst *Ret = dyn_cast<ReturnInst>(I->getTerminator()))
> @@ -778,23 +744,10 @@ static bool isFunctionMallocLike(Functio
> }
>
> /// Deduce noalias attributes for the SCC.
> -bool FunctionAttrs::AddNoAliasAttrs(const CallGraphSCC &SCC) {
> - SmallPtrSet<Function *, 8> SCCNodes;
> -
> - // Fill SCCNodes with the elements of the SCC. Used for quickly
> - // looking up whether a given CallGraphNode is in this SCC.
> - for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
> - SCCNodes.insert((*I)->getFunction());
> -
> +static bool addNoAliasAttrs(const SCCNodeSet &SCCNodes) {
> // Check each function in turn, determining which functions return noalias
> // pointers.
> - for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
> - Function *F = (*I)->getFunction();
> -
> - if (!F || F->hasFnAttribute(Attribute::OptimizeNone))
> - // External node or node we don't want to optimize - skip it;
> - return false;
> -
> + for (Function *F : SCCNodes) {
> // Already noalias.
> if (F->doesNotAlias(0))
> continue;
> @@ -814,8 +767,7 @@ bool FunctionAttrs::AddNoAliasAttrs(cons
> }
>
> bool MadeChange = false;
> - for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
> - Function *F = (*I)->getFunction();
> + for (Function *F : SCCNodes) {
> if (F->doesNotAlias(0) || !F->getReturnType()->isPointerTy())
> continue;
>
> @@ -834,7 +786,7 @@ bool FunctionAttrs::AddNoAliasAttrs(cons
> /// Returns true if it believes the function will not return a null, and sets
> /// \p Speculative based on whether the returned conclusion is a speculative
> /// conclusion due to SCC calls.
> -static bool isReturnNonNull(Function *F, SmallPtrSet<Function *, 8> &SCCNodes,
> +static bool isReturnNonNull(Function *F, const SCCNodeSet &SCCNodes,
> const TargetLibraryInfo &TLI, bool &Speculative) {
> assert(F->getReturnType()->isPointerTy() &&
> "nonnull only meaningful on pointer types");
> @@ -898,14 +850,8 @@ static bool isReturnNonNull(Function *F,
> }
>
> /// Deduce nonnull attributes for the SCC.
> -bool FunctionAttrs::AddNonNullAttrs(const CallGraphSCC &SCC) {
> - SmallPtrSet<Function *, 8> SCCNodes;
> -
> - // Fill SCCNodes with the elements of the SCC. Used for quickly
> - // looking up whether a given CallGraphNode is in this SCC.
> - for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
> - SCCNodes.insert((*I)->getFunction());
> -
> +static bool addNonNullAttrs(const SCCNodeSet &SCCNodes,
> + const TargetLibraryInfo &TLI) {
> // Speculative that all functions in the SCC return only nonnull
> // pointers. We may refute this as we analyze functions.
> bool SCCReturnsNonNull = true;
> @@ -914,13 +860,7 @@ bool FunctionAttrs::AddNonNullAttrs(cons
>
> // Check each function in turn, determining which functions return nonnull
> // pointers.
> - for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
> - Function *F = (*I)->getFunction();
> -
> - if (!F || F->hasFnAttribute(Attribute::OptimizeNone))
> - // External node or node we don't want to optimize - skip it;
> - return false;
> -
> + for (Function *F : SCCNodes) {
> // Already nonnull.
> if (F->getAttributes().hasAttribute(AttributeSet::ReturnIndex,
> Attribute::NonNull))
> @@ -937,7 +877,7 @@ bool FunctionAttrs::AddNonNullAttrs(cons
> continue;
>
> bool Speculative = false;
> - if (isReturnNonNull(F, SCCNodes, *TLI, Speculative)) {
> + if (isReturnNonNull(F, SCCNodes, TLI, Speculative)) {
> if (!Speculative) {
> // Mark the function eagerly since we may discover a function
> // which prevents us from speculating about the entire SCC
> @@ -954,8 +894,7 @@ bool FunctionAttrs::AddNonNullAttrs(cons
> }
>
> if (SCCReturnsNonNull) {
> - for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
> - Function *F = (*I)->getFunction();
> + for (Function *F : SCCNodes) {
> if (F->getAttributes().hasAttribute(AttributeSet::ReturnIndex,
> Attribute::NonNull) ||
> !F->getReturnType()->isPointerTy())
> @@ -1835,10 +1774,36 @@ bool FunctionAttrs::annotateLibraryCalls
> bool FunctionAttrs::runOnSCC(CallGraphSCC &SCC) {
> TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
>
> + // Annotate declarations for which we have special knowledge.
> bool Changed = annotateLibraryCalls(SCC);
> - Changed |= AddReadAttrs(SCC);
> - Changed |= AddArgumentAttrs(SCC);
> - Changed |= AddNoAliasAttrs(SCC);
> - Changed |= AddNonNullAttrs(SCC);
> +
> + // Fill SCCNodes with the elements of the SCC. Used for quickly looking up
> + // whether a given CallGraphNode is in this SCC. Also track whether there are
> + // any external or opt-none nodes that will prevent us from optimizing any
> + // part of the SCC.
> + SCCNodeSet SCCNodes;
> + bool ExternalNode = false;
> + for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
> + Function *F = (*I)->getFunction();
> + if (!F || F->hasFnAttribute(Attribute::OptimizeNone)) {
> + // External node or function we're trying not to optimize - we both avoid
> + // transform them and avoid leveraging information they provide.
> + ExternalNode = true;
> + continue;
> + }
> +
> + SCCNodes.insert(F);
> + }
> +
> + Changed |= AddReadAttrs(SCCNodes);
> + Changed |= addArgumentAttrs(SCCNodes);
> +
> + // If we have no external nodes participating in the SCC, we can infer some
> + // more precise attributes as well.
> + if (!ExternalNode) {
> + Changed |= addNoAliasAttrs(SCCNodes);
> + Changed |= addNonNullAttrs(SCCNodes, *TLI);
> + }
> +
> return Changed;
> }
>
>
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