Imported Upstream version 5.18.0.246

Former-commit-id: 0c7ce5b1a7851e13f22acfd379b7f9fb304e4833

external/llvm/lib/Transforms/Utils/DemoteRegToStack.cpp

@@ -0,0 +1,151 @@
+//===- DemoteRegToStack.cpp - Move a virtual register to the stack --------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/Analysis/CFG.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Type.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Local.h"
+using namespace llvm;
+
+/// 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, bool VolatileLoads,
+                                   Instruction *AllocaPoint) {
+  if (I.use_empty()) {
+    I.eraseFromParent();
+    return nullptr;
+  }
+
+  Function *F = I.getParent()->getParent();
+  const DataLayout &DL = F->getParent()->getDataLayout();
+
+  // Create a stack slot to hold the value.
+  AllocaInst *Slot;
+  if (AllocaPoint) {
+    Slot = new AllocaInst(I.getType(), DL.getAllocaAddrSpace(), nullptr,
+                          I.getName()+".reg2mem", AllocaPoint);
+  } else {
+    Slot = new AllocaInst(I.getType(), DL.getAllocaAddrSpace(), nullptr,
+                          I.getName() + ".reg2mem", &F->getEntryBlock().front());
+  }
+
+  // We cannot demote invoke instructions to the stack if their normal edge
+  // is critical. Therefore, split the critical edge and create a basic block
+  // into which the store can be inserted.
+  if (InvokeInst *II = dyn_cast<InvokeInst>(&I)) {
+    if (!II->getNormalDest()->getSinglePredecessor()) {
+      unsigned SuccNum = GetSuccessorNumber(II->getParent(), II->getNormalDest());
+      assert(isCriticalEdge(II, SuccNum) && "Expected a critical edge!");
+      BasicBlock *BB = SplitCriticalEdge(II, SuccNum);
+      assert(BB && "Unable to split critical edge.");
+      (void)BB;
+    }
+  }
+
+  // Change all of the users of the instruction to read from the stack slot.
+  while (!I.use_empty()) {
+    Instruction *U = cast<Instruction>(I.user_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 cannot have multiple loads. The problem is that the
+      // resulting PHI node will have multiple values (from each load) coming in
+      // from the same block, which is illegal SSA form. For this reason, we
+      // keep track of and reuse loads we insert.
+      DenseMap<BasicBlock*, Value*> Loads;
+      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+        if (PN->getIncomingValue(i) == &I) {
+          Value *&V = Loads[PN->getIncomingBlock(i)];
+          if (!V) {
+            // Insert the load into the predecessor block
+            V = new LoadInst(Slot, I.getName()+".reload", VolatileLoads,
+                             PN->getIncomingBlock(i)->getTerminator());
+          }
+          PN->setIncomingValue(i, V);
+        }
+
+    } else {
+      // If this is a normal instruction, just insert a load.
+      Value *V = new LoadInst(Slot, I.getName()+".reload", VolatileLoads, U);
+      U->replaceUsesOfWith(&I, V);
+    }
+  }
+
+  // Insert stores of the computed value into the stack slot. We have to be
+  // careful if I is an invoke instruction, because we can't insert the store
+  // AFTER the terminator instruction.
+  BasicBlock::iterator InsertPt;
+  if (!isa<TerminatorInst>(I)) {
+    InsertPt = ++I.getIterator();
+    for (; isa<PHINode>(InsertPt) || InsertPt->isEHPad(); ++InsertPt)
+      /* empty */;   // Don't insert before PHI nodes or landingpad instrs.
+  } else {
+    InvokeInst &II = cast<InvokeInst>(I);
+    InsertPt = II.getNormalDest()->getFirstInsertionPt();
+  }
+
+  new StoreInst(&I, Slot, &*InsertPt);
+  return Slot;
+}
+
+/// DemotePHIToStack - This function takes a virtual register computed by a PHI
+/// node and replaces it with a slot in the stack frame allocated via alloca.
+/// The PHI node is deleted. It returns the pointer to the alloca inserted.
+AllocaInst *llvm::DemotePHIToStack(PHINode *P, Instruction *AllocaPoint) {
+  if (P->use_empty()) {
+    P->eraseFromParent();
+    return nullptr;
+  }
+
+  const DataLayout &DL = P->getModule()->getDataLayout();
+
+  // Create a stack slot to hold the value.
+  AllocaInst *Slot;
+  if (AllocaPoint) {
+    Slot = new AllocaInst(P->getType(), DL.getAllocaAddrSpace(), nullptr,
+                          P->getName()+".reg2mem", AllocaPoint);
+  } else {
+    Function *F = P->getParent()->getParent();
+    Slot = new AllocaInst(P->getType(), DL.getAllocaAddrSpace(), nullptr,
+                          P->getName() + ".reg2mem",
+                          &F->getEntryBlock().front());
+  }
+
+  // Iterate over each operand inserting a store in each predecessor.
+  for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
+    if (InvokeInst *II = dyn_cast<InvokeInst>(P->getIncomingValue(i))) {
+      assert(II->getParent() != P->getIncomingBlock(i) &&
+             "Invoke edge not supported yet"); (void)II;
+    }
+    new StoreInst(P->getIncomingValue(i), Slot,
+                  P->getIncomingBlock(i)->getTerminator());
+  }
+
+  // Insert a load in place of the PHI and replace all uses.
+  BasicBlock::iterator InsertPt = P->getIterator();
+
+  for (; isa<PHINode>(InsertPt) || InsertPt->isEHPad(); ++InsertPt)
+    /* empty */;   // Don't insert before PHI nodes or landingpad instrs.
+
+  Value *V = new LoadInst(Slot, P->getName() + ".reload", &*InsertPt);
+  P->replaceAllUsesWith(V);
+
+  // Delete PHI.
+  P->eraseFromParent();
+  return Slot;
+}