[llvm-commits] CVS: llvm/lib/Transforms/Utils/DemoteRegToStack.cpp
Chris Lattner
lattner at cs.uiuc.edu
Tue Mar 16 17:24:01 PST 2004
Changes in directory llvm/lib/Transforms/Utils:
DemoteRegToStack.cpp updated: 1.9 -> 1.10
---
Log message:
This code was both incredibly complex and incredibly broken. Fix it.
---
Diffs of the changes: (+58 -138)
Index: llvm/lib/Transforms/Utils/DemoteRegToStack.cpp
diff -u llvm/lib/Transforms/Utils/DemoteRegToStack.cpp:1.9 llvm/lib/Transforms/Utils/DemoteRegToStack.cpp:1.10
--- llvm/lib/Transforms/Utils/DemoteRegToStack.cpp:1.9 Sat Mar 13 20:13:34 2004
+++ llvm/lib/Transforms/Utils/DemoteRegToStack.cpp Tue Mar 16 17:23:11 2004
@@ -8,156 +8,76 @@
//===----------------------------------------------------------------------===//
//
// This file provide the function DemoteRegToStack(). This function takes a
-// virtual register computed by an Instruction& X and replaces it with a slot in
+// virtual register computed by an Instruction and replaces it with a slot in
// the stack frame, allocated via alloca. It returns the pointer to the
-// AllocaInst inserted.
+// AllocaInst inserted. After this function is called on an instruction, we are
+// guaranteed that the only user of the instruction is a store that is
+// immediately after it.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Function.h"
-#include "llvm/iMemory.h"
-#include "llvm/iPHINode.h"
-#include "llvm/iTerminators.h"
-#include "llvm/Type.h"
-#include "Support/hash_set"
+#include "llvm/Instructions.h"
using namespace llvm;
-typedef hash_set<PHINode*> PhiSet;
-typedef hash_set<PHINode*>::iterator PhiSetIterator;
-
-// Helper function to push a phi *and* all its operands to the worklist!
-// Do not push an instruction if it is already in the result set of Phis to go.
-static inline void PushOperandsOnWorkList(std::vector<Instruction*>& workList,
- PhiSet& phisToGo, PHINode* phiN) {
- for (User::op_iterator OI = phiN->op_begin(), OE = phiN->op_end();
- OI != OE; ++OI) {
- Instruction* opI = cast<Instruction>(OI);
- if (!isa<PHINode>(opI) || !phisToGo.count(cast<PHINode>(opI)))
- workList.push_back(opI);
- }
-}
-
-static void FindPhis(Instruction& X, PhiSet& phisToGo) {
- std::vector<Instruction*> workList;
- workList.push_back(&X);
-
- // Handle the case that X itself is a Phi!
- if (PHINode* phiX = dyn_cast<PHINode>(&X)) {
- phisToGo.insert(phiX);
- PushOperandsOnWorkList(workList, phisToGo, phiX);
- }
-
- // Now use a worklist to find all phis reachable from X, and
- // (recursively) all phis reachable from operands of such phis.
- while (!workList.empty()) {
- Instruction *I = workList.back();
- workList.pop_back();
- for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI)
- if (PHINode* phiN = dyn_cast<PHINode>(*UI))
- if (phisToGo.find(phiN) == phisToGo.end()) {
- // Seeing this phi for the first time: it must go!
- phisToGo.insert(phiN);
- workList.push_back(phiN);
- PushOperandsOnWorkList(workList, phisToGo, phiN);
+/// DemoteRegToStack - This function takes a virtual register computed by an
+/// Instruction and replaces it with a slot in the stack frame, allocated via
+/// alloca. This allows the CFG to be changed around without fear of
+/// invalidating the SSA information for the value. It returns the pointer to
+/// the alloca inserted to create a stack slot for I.
+///
+AllocaInst* llvm::DemoteRegToStack(Instruction &I) {
+ if (I.use_empty()) return 0; // nothing to do!
+
+ // Create a stack slot to hold the value.
+ Function *F = I.getParent()->getParent();
+ AllocaInst *Slot = new AllocaInst(I.getType(), 0, I.getName(),
+ F->getEntryBlock().begin());
+
+ // Change all of the users of the instruction to read from the stack slot
+ // instead.
+ while (!I.use_empty()) {
+ Instruction *U = cast<Instruction>(I.use_back());
+ if (PHINode *PN = dyn_cast<PHINode>(U)) {
+ // If this is a PHI node, we can't insert a load of the value before the
+ // use. Instead, insert the load in the predecessor block corresponding
+ // to the incoming value.
+ //
+ // Note that if there are multiple edges from a basic block to this PHI
+ // node that we'll insert multiple loads. Since DemoteRegToStack requires
+ // a mem2reg pass after it (to produce reasonable code), we don't care.
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (PN->getIncomingValue(i) == &I) {
+ // Insert the load into the predecessor block
+ Value *V = new LoadInst(Slot, I.getName()+".reload",
+ PN->getIncomingBlock(i)->getTerminator());
+ PN->setIncomingValue(i, V);
}
- }
-}
-
-// Insert loads before all uses of I, except uses in Phis
-// since all such Phis *must* be deleted.
-static void LoadBeforeUses(Instruction* def, AllocaInst* XSlot) {
- for (unsigned nPhis = 0; def->use_size() - nPhis > 0; ) {
- Instruction* useI = cast<Instruction>(def->use_back());
- if (!isa<PHINode>(useI)) {
- LoadInst* loadI =
- new LoadInst(XSlot, std::string("Load")+XSlot->getName(), useI);
- useI->replaceUsesOfWith(def, loadI);
- } else
- ++nPhis;
- }
-}
-
-static void AddLoadsAndStores(AllocaInst* XSlot, Instruction& X,
- PhiSet& phisToGo) {
- for (PhiSetIterator PI=phisToGo.begin(), PE=phisToGo.end(); PI != PE; ++PI) {
- PHINode* pn = *PI;
-
- // First, insert loads before all uses except uses in Phis.
- // Do this first because new stores will appear as uses also!
- LoadBeforeUses(pn, XSlot);
-
- // For every incoming operand of the Phi, insert a store either
- // just after the instruction defining the value or just before the
- // predecessor of the Phi if the value is a formal, not an instruction.
- //
- for (unsigned i=0, N=pn->getNumIncomingValues(); i < N; ++i) {
- Value* phiOp = pn->getIncomingValue(i);
- if (phiOp != &X &&
- (!isa<PHINode>(phiOp) || !phisToGo.count(cast<PHINode>(phiOp)))) {
- // This operand is not a phi that will be deleted: need to store.
- assert(!isa<TerminatorInst>(phiOp));
-
- Instruction* storeBefore;
- if (Instruction* I = dyn_cast<Instruction>(phiOp)) {
- // phiOp is an instruction, store its result right after it.
- assert(I->getNext() && "Non-terminator without successor?");
- storeBefore = I->getNext();
- } else {
- // If not, it must be a formal: store it at the end of the
- // predecessor block of the Phi (*not* at function entry!).
- storeBefore = pn->getIncomingBlock(i)->getTerminator();
- }
-
- // Create instr. to store the value of phiOp before `insertBefore'
- StoreInst* storeI = new StoreInst(phiOp, XSlot, storeBefore);
- }
+ } else {
+ // If this is a normal instruction, just insert a load.
+ Value *V = new LoadInst(Slot, I.getName()+".reload", U);
+ U->replaceUsesOfWith(&I, V);
}
}
-}
-//----------------------------------------------------------------------------
-// function DemoteRegToStack()
-//
-// This function takes a virtual register computed by an
-// Instruction& X and replaces it with a slot in the stack frame,
-// allocated via alloca. It has to:
-// (1) Identify all Phi operations that have X as an operand and
-// transitively other Phis that use such Phis;
-// (2) Store all values merged with X via Phi operations to the stack slot;
-// (3) Load the value from the stack slot just before any use of X or any
-// of the Phis that were eliminated; and
-// (4) Delete all the Phis, which should all now be dead.
-//
-// Returns the pointer to the alloca inserted to create a stack slot for X.
-//
-AllocaInst* llvm::DemoteRegToStack(Instruction& X) {
- if (X.getType() == Type::VoidTy)
- return 0; // nothing to do!
-
- // Find all Phis involving X or recursively using such Phis or Phis
- // involving operands of such Phis (essentially all Phis in the "web" of X)
- PhiSet phisToGo;
- FindPhis(X, phisToGo);
-
- // Create a stack slot to hold X
- Function* parentFunc = X.getParent()->getParent();
- AllocaInst *XSlot = new AllocaInst(X.getType(), 0, X.getName(),
- parentFunc->getEntryBlock().begin());
-
-
- // Insert loads before all uses of X and (*only then*) insert store after X
- assert(X.getNext() && "Non-terminator (since non-void) with no successor?");
- LoadBeforeUses(&X, XSlot);
- StoreInst* storeI = new StoreInst(&X, XSlot, X.getNext());
-
- // Do the same for all the phis that will be deleted
- AddLoadsAndStores(XSlot, X, phisToGo);
-
- // Delete the phis and return the alloca instruction
- for (PhiSetIterator PI = phisToGo.begin(), E = phisToGo.end(); PI != E; ++PI)
- (*PI)->getParent()->getInstList().erase(*PI);
- return XSlot;
+ // Insert stores of the computed value into the stack slot. We have to be
+ // careful is I is an invoke instruction though, because we can't insert the
+ // store AFTER the terminator instruction.
+ if (!isa<TerminatorInst>(I)) {
+ BasicBlock::iterator InsertPt = &I;
+ for (++InsertPt; isa<PHINode>(InsertPt); ++InsertPt)
+ /* empty */; // Don't insert before any PHI nodes.
+ new StoreInst(&I, Slot, InsertPt);
+ } else {
+ // FIXME: We cannot yet demote invoke instructions to the stack, because
+ // doing so would require breaking critical edges. This should be fixed
+ // eventually.
+ assert(0 &&
+ "Cannot demote the value computed by an invoke instruction yet!");
+ }
+
+ return Slot;
}
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