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Enhance GVN to propagate simple conditionals. This fixes PR3921.
llvm-svn: 68172
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@ -121,6 +121,7 @@ namespace {
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AliasAnalysis* AA;
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MemoryDependenceAnalysis* MD;
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DominatorTree* DT;
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uint32_t true_vn, false_vn;
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uint32_t nextValueNumber;
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@ -138,7 +139,14 @@ namespace {
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Expression create_expression(CallInst* C);
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Expression create_expression(Constant* C);
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public:
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ValueTable() : nextValueNumber(1) { }
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ValueTable() : nextValueNumber(1) {
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true_vn = lookup_or_add(ConstantInt::getTrue());
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false_vn = lookup_or_add(ConstantInt::getFalse());
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}
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uint32_t getTrueVN() { return true_vn; }
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uint32_t getFalseVN() { return false_vn; }
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uint32_t lookup_or_add(Value* V);
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uint32_t lookup(Value* V) const;
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void add(Value* V, uint32_t num);
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@ -1294,9 +1302,27 @@ bool GVN::processInstruction(Instruction *I,
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uint32_t nextNum = VN.getNextUnusedValueNumber();
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unsigned num = VN.lookup_or_add(I);
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if (BranchInst* BI = dyn_cast<BranchInst>(I)) {
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localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
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if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
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return false;
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Value* branchCond = BI->getCondition();
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uint32_t condVN = VN.lookup_or_add(branchCond);
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BasicBlock* trueSucc = BI->getSuccessor(0);
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BasicBlock* falseSucc = BI->getSuccessor(1);
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localAvail[trueSucc]->table.insert(std::make_pair(condVN,
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ConstantInt::getTrue()));
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localAvail[falseSucc]->table.insert(std::make_pair(condVN,
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ConstantInt::getFalse()));
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return false;
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// Allocations are always uniquely numbered, so we can save time and memory
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// by fast failing them.
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if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
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// by fast failing them.
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} else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
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localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
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return false;
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}
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@ -1405,18 +1431,11 @@ bool GVN::runOnFunction(Function& F) {
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bool GVN::processBlock(BasicBlock* BB) {
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DomTreeNode* DTN = DT->getNode(BB);
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// FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
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// incrementing BI before processing an instruction).
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SmallVector<Instruction*, 8> toErase;
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bool changed_function = false;
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if (DTN->getIDom())
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localAvail[BB] =
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new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]);
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else
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localAvail[BB] = new ValueNumberScope(0);
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for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
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BI != BE;) {
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changed_function |= processInstruction(BI, toErase);
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@ -1607,6 +1626,15 @@ bool GVN::performPRE(Function& F) {
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bool GVN::iterateOnFunction(Function &F) {
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cleanupGlobalSets();
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for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
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DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
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if (DI->getIDom())
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localAvail[DI->getBlock()] =
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new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
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else
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localAvail[DI->getBlock()] = new ValueNumberScope(0);
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}
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// Top-down walk of the dominator tree
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bool changed = false;
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#if 0
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52
test/Transforms/GVN/condprop.ll
Normal file
52
test/Transforms/GVN/condprop.ll
Normal file
@ -0,0 +1,52 @@
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; RUN: llvm-as < %s | opt -gvn | llvm-dis | grep {br i1 false}
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@a = external global i32 ; <i32*> [#uses=7]
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define i32 @foo() nounwind {
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entry:
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%0 = load i32* @a, align 4 ; <i32> [#uses=1]
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%1 = icmp eq i32 %0, 4 ; <i1> [#uses=1]
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br i1 %1, label %bb, label %bb1
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bb: ; preds = %entry
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br label %bb8
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bb1: ; preds = %entry
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%2 = load i32* @a, align 4 ; <i32> [#uses=1]
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%3 = icmp eq i32 %2, 5 ; <i1> [#uses=1]
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br i1 %3, label %bb2, label %bb3
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bb2: ; preds = %bb1
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br label %bb8
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bb3: ; preds = %bb1
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%4 = load i32* @a, align 4 ; <i32> [#uses=1]
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%5 = icmp eq i32 %4, 4 ; <i1> [#uses=1]
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br i1 %5, label %bb4, label %bb5
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bb4: ; preds = %bb3
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%6 = load i32* @a, align 4 ; <i32> [#uses=1]
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%7 = add i32 %6, 5 ; <i32> [#uses=1]
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br label %bb8
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bb5: ; preds = %bb3
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%8 = load i32* @a, align 4 ; <i32> [#uses=1]
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%9 = icmp eq i32 %8, 5 ; <i1> [#uses=1]
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br i1 %9, label %bb6, label %bb7
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bb6: ; preds = %bb5
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%10 = load i32* @a, align 4 ; <i32> [#uses=1]
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%11 = add i32 %10, 4 ; <i32> [#uses=1]
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br label %bb8
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bb7: ; preds = %bb5
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%12 = load i32* @a, align 4 ; <i32> [#uses=1]
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br label %bb8
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bb8: ; preds = %bb7, %bb6, %bb4, %bb2, %bb
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%.0 = phi i32 [ %12, %bb7 ], [ %11, %bb6 ], [ %7, %bb4 ], [ 4, %bb2 ], [ 5, %bb ] ; <i32> [#uses=1]
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br label %return
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return: ; preds = %bb8
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ret i32 %.0
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}
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