PreservedAnalyses run(Function &F, FunctionAnalysisManager &);
private:
- void BuildRankMap(Function &F);
+ void BuildRankMap(Function &F, ReversePostOrderTraversal<Function *> &RPOT);
unsigned getRank(Value *V);
void canonicalizeOperands(Instruction *I);
void ReassociateExpression(BinaryOperator *I);
return nullptr;
}
-void ReassociatePass::BuildRankMap(Function &F) {
+void ReassociatePass::BuildRankMap(Function &F,
+ ReversePostOrderTraversal<Function*> &RPOT) {
unsigned i = 2;
// Assign distinct ranks to function arguments.
DEBUG(dbgs() << "Calculated Rank[" << I->getName() << "] = " << i << "\n");
}
- ReversePostOrderTraversal<Function *> RPOT(&F);
+ // Traverse basic blocks in ReversePostOrder
for (BasicBlock *BB : RPOT) {
unsigned BBRank = RankMap[BB] = ++i << 16;
}
PreservedAnalyses ReassociatePass::run(Function &F, FunctionAnalysisManager &) {
+ // Get the functions basic blocks in Reverse Post Order. This order is used by
+ // BuildRankMap to pre calculate ranks correctly. It also excludes dead basic
+ // blocks (it has been seen that the analysis in this pass could hang when
+ // analysing dead basic blocks).
+ ReversePostOrderTraversal<Function *> RPOT(&F);
+
// Calculate the rank map for F.
- BuildRankMap(F);
+ BuildRankMap(F, RPOT);
MadeChange = false;
- for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
+ // Traverse the same blocks that was analysed by BuildRankMap.
+ for (BasicBlock *BI : RPOT) {
+ assert(RankMap.count(&*BI) && "BB should be ranked.");
// Optimize every instruction in the basic block.
for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE;)
if (isInstructionTriviallyDead(&*II)) {
--- /dev/null
+; RUN: opt < %s -reassociate -disable-output
+
+; It has been detected that dead loops like the one in this test case can be
+; created by -jump-threading (it was detected by a csmith generated program).
+;
+; According to -verify this is valid input (even if it could be discussed if
+; the dead loop really satisfies SSA form).
+;
+; The problem found was that the -reassociate pass ends up in an infinite loop
+; when analysing the 'deadloop1' basic block. See "Bugzilla - Bug 30818".
+define void @deadloop1() {
+ br label %endlabel
+
+deadloop1:
+ %1 = xor i32 %2, 7
+ %2 = xor i32 %1, 8
+ br label %deadloop1
+
+endlabel:
+ ret void
+}
+
+
+; Another example showing that dead code could result in infinite loops in
+; reassociate pass. See "Bugzilla - Bug 30818".
+define void @deadloop2() {
+ br label %endlabel
+
+deadloop2:
+ %1 = and i32 %2, 7
+ %2 = and i32 %3, 8
+ %3 = and i32 %1, 6
+ br label %deadloop2
+
+endlabel:
+ ret void
+}