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Fairly substantial changes to update the alias analysis we are querying as
we make the transformation. This allows us to use interprocedural alias analyses successfully. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13691 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -1,4 +1,4 @@
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//===-- ArgumentPromotion.cpp - Promote 'by reference' arguments ----------===//
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//===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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@ -12,14 +12,14 @@
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// arguments. If we can prove, through the use of alias analysis, that that an
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// argument is *only* loaded, then we can pass the value into the function
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// instead of the address of the value. This can cause recursive simplification
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// of code, and lead to the elimination of allocas, especially in C++ template
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// code like the STL.
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// of code and lead to the elimination of allocas (especially in C++ template
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// code like the STL).
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//
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// This pass also handles aggregate arguments that are passed into a function,
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// scalarizing them if the elements of the aggregate are only loaded. Note that
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// we refuse to scalarize aggregates which would require passing in more than
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// three operands to the function, because we don't want to pass thousands of
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// operands for a large array or something!
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// operands for a large array or structure!
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//
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// Note that this transformation could also be done for arguments that are only
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// stored to (returning the value instead), but we do not currently handle that
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@ -28,6 +28,7 @@
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "argpromotion"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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@ -58,7 +59,7 @@ namespace {
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class ArgPromotion : public Pass {
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// WorkList - The set of internal functions that we have yet to process. As
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// we eliminate arguments from a function, we push all callers into this set
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// so that the by reference argument can be bubbled out as far as possible.
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// so that the by-reference argument can be bubbled out as far as possible.
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// This set contains only internal functions.
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std::set<Function*> WorkList;
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public:
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@ -128,7 +129,11 @@ bool ArgPromotion::run(Module &M) {
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return Changed;
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}
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/// PromoteArguments - This method checks the specified function to see if there
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/// are any promotable arguments and if it is safe to promote the function (for
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/// example, all callers are direct). If safe to promote some arguments, it
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/// calls the DoPromotion method.
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///
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bool ArgPromotion::PromoteArguments(Function *F) {
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assert(F->hasInternalLinkage() && "We can only process internal functions!");
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@ -144,15 +149,14 @@ bool ArgPromotion::PromoteArguments(Function *F) {
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for (Value::use_iterator UI = F->use_begin(), E = F->use_end();
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UI != E; ++UI) {
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CallSite CS = CallSite::get(*UI);
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if (Instruction *I = CS.getInstruction()) {
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// Ensure that this call site is CALLING the function, not passing it as
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// an argument.
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for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
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AI != E; ++AI)
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if (*AI == F) return false; // Passing the function address in!
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} else {
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return false; // Cannot promote an indirect call!
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}
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if (!CS.getInstruction()) // "Taking the address" of the function
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return false;
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// Ensure that this call site is CALLING the function, not passing it as
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// an argument.
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for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
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AI != E; ++AI)
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if (*AI == F) return false; // Passing the function address in!
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}
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// Check to see which arguments are promotable. If an argument is not
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@ -171,6 +175,12 @@ bool ArgPromotion::PromoteArguments(Function *F) {
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return true;
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}
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/// isSafeToPromoteArgument - As you might guess from the name of this method,
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/// it checks to see if it is both safe and useful to promote the argument.
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/// This method limits promotion of aggregates to only promote up to three
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/// elements of the aggregate in order to avoid exploding the number of
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/// arguments passed in.
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bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
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// We can only promote this argument if all of the uses are loads, or are GEP
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// instructions (with constant indices) that are subsequently loaded.
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@ -185,6 +195,7 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
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if (GEP->use_empty()) {
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// Dead GEP's cause trouble later. Just remove them if we run into
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// them.
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getAnalysis<AliasAnalysis>().deleteValue(GEP);
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GEP->getParent()->getInstList().erase(GEP);
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return isSafeToPromoteArgument(Arg);
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}
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@ -206,12 +217,15 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
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return false;
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}
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// See if there is already a GEP with these indices. If so, check to make
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// sure that we aren't promoting too many elements. If not, nothing to
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// do.
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// See if there is already a GEP with these indices. If not, check to
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// make sure that we aren't promoting too many elements. If so, nothing
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// to do.
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if (std::find(GEPIndices.begin(), GEPIndices.end(), Operands) ==
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GEPIndices.end()) {
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if (GEPIndices.size() == 3) {
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DEBUG(std::cerr << "argpromotion disable promoting argument '"
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<< Arg->getName() << "' because it would require adding more "
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<< "than 3 arguments to the function.\n");
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// We limit aggregate promotion to only promoting up to three elements
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// of the aggregate.
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return false;
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@ -222,11 +236,11 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
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return false; // Not a load or a GEP.
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}
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if (Loads.empty()) return true; // No users, dead argument.
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if (Loads.empty()) return true; // No users, this is a dead argument.
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// Okay, now we know that the argument is only used by load instructions.
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// Check to see if the pointer is guaranteed to not be modified from entry of
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// the function to each of the load instructions.
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// Okay, now we know that the argument is only used by load instructions. Use
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// alias analysis to check to see if the pointer is guaranteed to not be
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// modified from entry of the function to each of the load instructions.
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Function &F = *Arg->getParent();
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// Because there could be several/many load instructions, remember which
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@ -265,7 +279,8 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
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return true;
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}
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/// DoPromotion - This method actually performs the promotion of the specified
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/// arguments. At this point, we know that it's safe to do so.
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void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
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std::set<Argument*> ArgsToPromote(Args2Prom.begin(), Args2Prom.end());
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@ -283,10 +298,17 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
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//
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std::map<Argument*, std::set<std::vector<Value*> > > ScalarizedElements;
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// OriginalLoads - Keep track of a representative load instruction from the
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// original function so that we can tell the alias analysis implementation
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// what the new GEP/Load instructions we are inserting look like.
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std::map<std::vector<Value*>, LoadInst*> OriginalLoads;
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for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
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if (!ArgsToPromote.count(I)) {
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Params.push_back(I->getType());
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} else if (!I->use_empty()) {
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} else if (I->use_empty()) {
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++NumArgumentsDead;
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} else {
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// Okay, this is being promoted. Check to see if there are any GEP uses
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// of the argument.
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std::set<std::vector<Value*> > &ArgIndices = ScalarizedElements[I];
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@ -294,8 +316,14 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
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++UI) {
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Instruction *User = cast<Instruction>(*UI);
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assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User));
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ArgIndices.insert(std::vector<Value*>(User->op_begin()+1,
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User->op_end()));
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std::vector<Value*> Indices(User->op_begin()+1, User->op_end());
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ArgIndices.insert(Indices);
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LoadInst *OrigLoad;
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if (LoadInst *L = dyn_cast<LoadInst>(User))
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OrigLoad = L;
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else
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OrigLoad = cast<LoadInst>(User->use_back());
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OriginalLoads[Indices] = OrigLoad;
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}
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// Add a parameter to the function for each element passed in.
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@ -307,8 +335,6 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
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++NumArgumentsPromoted;
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else
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++NumAggregatesPromoted;
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} else {
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++NumArgumentsDead;
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}
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const Type *RetTy = FTy->getReturnType();
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@ -325,7 +351,11 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
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// Create the new function body and insert it into the module...
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Function *NF = new Function(NFTy, F->getLinkage(), F->getName());
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F->getParent()->getFunctionList().insert(F, NF);
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// Get the alias analysis information that we need to update to reflect our
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// changes.
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AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
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// Loop over all of the callers of the function, transforming the call sites
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// to pass in the loaded pointers.
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//
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@ -334,25 +364,30 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
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CallSite CS = CallSite::get(F->use_back());
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Instruction *Call = CS.getInstruction();
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// Make sure the caller of this function is revisited.
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// Make sure the caller of this function is revisited now that we promoted
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// arguments in a callee of it.
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if (Call->getParent()->getParent()->hasInternalLinkage())
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WorkList.insert(Call->getParent()->getParent());
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// Loop over the operands, deleting dead ones...
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// Loop over the operands, inserting GEP and loads in the caller as
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// appropriate.
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CallSite::arg_iterator AI = CS.arg_begin();
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for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I, ++AI)
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if (!ArgsToPromote.count(I))
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Args.push_back(*AI); // Unmodified argument
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else if (!I->use_empty()) {
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// Non-dead argument.
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// Non-dead argument: insert GEPs and loads as appropriate.
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std::set<std::vector<Value*> > &ArgIndices = ScalarizedElements[I];
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for (std::set<std::vector<Value*> >::iterator SI = ArgIndices.begin(),
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E = ArgIndices.end(); SI != E; ++SI) {
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Value *V = *AI;
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if (!SI->empty())
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LoadInst *OrigLoad = OriginalLoads[*SI];
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if (!SI->empty()) {
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V = new GetElementPtrInst(V, *SI, V->getName()+".idx", Call);
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AA.copyValue(OrigLoad->getOperand(0), V);
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}
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Args.push_back(new LoadInst(V, V->getName()+".val", Call));
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AA.copyValue(OrigLoad, Args.back());
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}
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}
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@ -372,6 +407,10 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
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}
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Args.clear();
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// Update the alias analysis implementation to know that we are replacing
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// the old call with a new one.
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AA.replaceWithNewValue(Call, New);
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if (!Call->use_empty()) {
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Call->replaceAllUsesWith(New);
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std::string Name = Call->getName();
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@ -399,8 +438,11 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
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// new version.
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I->replaceAllUsesWith(I2);
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I2->setName(I->getName());
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AA.replaceWithNewValue(I, I2);
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++I2;
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} else if (!I->use_empty()) {
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} else if (I->use_empty()) {
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AA.deleteValue(I);
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} else {
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// Otherwise, if we promoted this argument, then all users are load
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// instructions, and all loads should be using the new argument that we
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// added.
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@ -412,9 +454,10 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
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"Load element should sort to front!");
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I2->setName(I->getName()+".val");
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LI->replaceAllUsesWith(I2);
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AA.replaceWithNewValue(LI, I2);
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LI->getParent()->getInstList().erase(LI);
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DEBUG(std::cerr << "*** Promoted argument '" << I->getName()
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<< "' of function '" << F->getName() << "'\n");
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DEBUG(std::cerr << "*** Promoted load of argument '" << I->getName()
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<< "' in function '" << F->getName() << "'\n");
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} else {
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GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back());
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std::vector<Value*> Operands(GEP->op_begin()+1, GEP->op_end());
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@ -442,20 +485,30 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
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while (!GEP->use_empty()) {
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LoadInst *L = cast<LoadInst>(GEP->use_back());
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L->replaceAllUsesWith(TheArg);
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AA.replaceWithNewValue(L, TheArg);
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L->getParent()->getInstList().erase(L);
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}
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AA.deleteValue(GEP);
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GEP->getParent()->getInstList().erase(GEP);
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}
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}
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// If we inserted a new pointer type, it's possible that IT could be
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// promoted too. Also, increment I2 past all of the arguments for this
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// pointer.
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// promoted too. Also, increment I2 past all of the arguments added for
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// this promoted pointer.
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for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i, ++I2)
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if (isa<PointerType>(I2->getType()))
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WorkList.insert(NF);
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}
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// Notify the alias analysis implementation that we inserted a new argument.
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if (ExtraArgHack)
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AA.copyValue(Constant::getNullValue(Type::IntTy), NF->abegin());
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// Tell the alias analysis that the old function is about to disappear.
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AA.replaceWithNewValue(F, NF);
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// Now that the old function is dead, delete it.
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F->getParent()->getFunctionList().erase(F);
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}
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