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Teach mergefunc how to emit aliases safely again -- but keep it turned it off
for now. It's controlled by the HasGlobalAliases variable which is not attached to any flag yet. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124182 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -68,6 +68,7 @@ using namespace llvm;
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STATISTIC(NumFunctionsMerged, "Number of functions merged");
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STATISTIC(NumThunksWritten, "Number of thunks generated");
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STATISTIC(NumAliasesWritten, "Number of aliases generated");
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STATISTIC(NumDoubleWeak, "Number of new functions created");
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/// ProfileFunction - Creates a hash-code for the function which is the same
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@ -164,7 +165,8 @@ namespace {
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class MergeFunctions : public ModulePass {
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public:
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static char ID;
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MergeFunctions() : ModulePass(ID) {
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MergeFunctions()
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: ModulePass(ID), HasGlobalAliases(false) {
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initializeMergeFunctionsPass(*PassRegistry::getPassRegistry());
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}
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@ -189,21 +191,34 @@ private:
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/// queue the functions.
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void RemoveUsers(Value *V);
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/// Replace all direct calls of Old with calls of New. Will bitcast New if
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/// necessary to make types match.
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void replaceDirectCallers(Function *Old, Function *New);
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/// MergeTwoFunctions - Merge two equivalent functions. Upon completion, G
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/// may be deleted, or may be converted into a thunk. In either case, it
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/// should never be visited again.
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void MergeTwoFunctions(Function *F, Function *G);
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/// WriteThunkOrAlias - Replace G with a thunk or an alias to F. Deletes G.
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void WriteThunkOrAlias(Function *F, Function *G);
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/// WriteThunk - Replace G with a simple tail call to bitcast(F). Also
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/// replace direct uses of G with bitcast(F). Deletes G.
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void WriteThunk(Function *F, Function *G);
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/// WriteAlias - Replace G with an alias to F. Deletes G.
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void WriteAlias(Function *F, Function *G);
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/// The set of all distinct functions. Use the Insert and Remove methods to
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/// modify it.
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FnSetType FnSet;
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/// TargetData for more accurate GEP comparisons. May be NULL.
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TargetData *TD;
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/// Whether or not the target supports global aliases.
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bool HasGlobalAliases;
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};
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} // end anonymous namespace
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@ -587,22 +602,39 @@ bool FunctionComparator::Compare() {
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return true;
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}
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/// Replace direct callers of Old with New.
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void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) {
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Constant *BitcastNew = ConstantExpr::getBitCast(New, Old->getType());
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for (Value::use_iterator UI = Old->use_begin(), UE = Old->use_end();
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UI != UE;) {
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Value::use_iterator TheIter = UI;
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++UI;
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CallSite CS(*TheIter);
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if (CS && CS.isCallee(TheIter)) {
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Remove(CS.getInstruction()->getParent()->getParent());
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TheIter.getUse().set(BitcastNew);
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}
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}
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}
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void MergeFunctions::WriteThunkOrAlias(Function *F, Function *G) {
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if (HasGlobalAliases && G->hasUnnamedAddr()) {
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if (G->hasExternalLinkage() || G->hasLocalLinkage() ||
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G->hasWeakLinkage()) {
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WriteAlias(F, G);
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return;
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}
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}
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WriteThunk(F, G);
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}
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/// WriteThunk - Replace G with a simple tail call to bitcast(F). Also replace
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/// direct uses of G with bitcast(F). Deletes G.
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void MergeFunctions::WriteThunk(Function *F, Function *G) {
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if (!G->mayBeOverridden()) {
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// Redirect direct callers of G to F.
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Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
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for (Value::use_iterator UI = G->use_begin(), UE = G->use_end();
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UI != UE;) {
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Value::use_iterator TheIter = UI;
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++UI;
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CallSite CS(*TheIter);
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if (CS && CS.isCallee(TheIter)) {
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Remove(CS.getInstruction()->getParent()->getParent());
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TheIter.getUse().set(BitcastF);
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}
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}
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replaceDirectCallers(G, F);
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}
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// If G was internal then we may have replaced all uses of G with F. If so,
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@ -645,31 +677,53 @@ void MergeFunctions::WriteThunk(Function *F, Function *G) {
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++NumThunksWritten;
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}
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/// WriteAlias - Replace G with an alias to F and delete G.
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void MergeFunctions::WriteAlias(Function *F, Function *G) {
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Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
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GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "",
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BitcastF, G->getParent());
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F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
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GA->takeName(G);
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GA->setVisibility(G->getVisibility());
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RemoveUsers(G);
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G->replaceAllUsesWith(GA);
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G->eraseFromParent();
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DEBUG(dbgs() << "WriteAlias: " << GA->getName() << '\n');
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++NumAliasesWritten;
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}
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/// MergeTwoFunctions - Merge two equivalent functions. Upon completion,
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/// Function G is deleted.
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void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) {
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if (F->mayBeOverridden()) {
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assert(G->mayBeOverridden());
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// Make them both thunks to the same internal function.
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Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
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F->getParent());
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H->copyAttributesFrom(F);
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H->takeName(F);
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RemoveUsers(F);
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F->replaceAllUsesWith(H);
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if (HasGlobalAliases) {
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// Make them both thunks to the same internal function.
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Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
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F->getParent());
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H->copyAttributesFrom(F);
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H->takeName(F);
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RemoveUsers(F);
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F->replaceAllUsesWith(H);
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unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment());
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unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment());
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WriteThunk(F, G);
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WriteThunk(F, H);
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WriteAlias(F, G);
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WriteAlias(F, H);
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F->setAlignment(MaxAlignment);
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F->setLinkage(GlobalValue::PrivateLinkage);
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F->setAlignment(MaxAlignment);
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F->setLinkage(GlobalValue::PrivateLinkage);
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} else {
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// We can't merge them. Instead, pick one and update all direct callers
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// to call it and hope that we improve the instruction cache hit rate.
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replaceDirectCallers(G, F);
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}
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++NumDoubleWeak;
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} else {
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WriteThunk(F, G);
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WriteThunkOrAlias(F, G);
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}
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++NumFunctionsMerged;
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@ -1,6 +1,10 @@
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; RUN: opt < %s -mergefunc -S > %t
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; RUN: grep {define weak} %t | count 2
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; RUN: grep {call} %t | count 2
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; XFAIL: *
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; This test is off for a bit as we change this particular sort of folding to
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; only apply on ELF systems and not Mach-O systems.
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define weak i32 @sum(i32 %x, i32 %y) {
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%sum = add i32 %x, %y
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