// Discard |def| and mine its operands for any subsequently dead defs. bool ValueNumberer::discardDef(MDefinition *def) { #ifdef DEBUG JitSpew(JitSpew_GVN, " Discarding %s %s%u", def->block()->isMarked() ? "unreachable" : "dead", def->opName(), def->id()); MOZ_ASSERT(def != nextDef_, "Invalidating the MDefinition iterator"); if (def->block()->isMarked()) { MOZ_ASSERT(!def->hasUses(), "Discarding def that still has uses"); } else { MOZ_ASSERT(IsDiscardable(def), "Discarding non-discardable definition"); MOZ_ASSERT(!values_.has(def), "Discarding a definition still in the set"); } #endif MBasicBlock *block = def->block(); if (def->isPhi()) { MPhi *phi = def->toPhi(); if (!releaseAndRemovePhiOperands(phi)) return false; MPhiIterator at(block->phisBegin(phi)); block->discardPhiAt(at); } else { MInstruction *ins = def->toInstruction(); if (MResumePoint *resume = ins->resumePoint()) { if (!releaseResumePointOperands(resume)) return false; } if (!releaseOperands(ins)) return false; block->discardIgnoreOperands(ins); } // If that was the last definition in the block, it can be safely removed // from the graph. if (block->phisEmpty() && block->begin() == block->end()) { MOZ_ASSERT(block->isMarked(), "Reachable block lacks at least a control instruction"); // As a special case, don't remove a block which is a dominator tree // root so that we don't invalidate the iterator in visitGraph. We'll // check for this and remove it later. if (block->immediateDominator() != block) { JitSpew(JitSpew_GVN, " Block block%u is now empty; discarding", block->id()); graph_.removeBlock(block); blocksRemoved_ = true; } else { JitSpew(JitSpew_GVN, " Dominator root block%u is now empty; will discard later", block->id()); } } return true; }