[NVPTX] fix a crash bug in NVPTXFavorNonGenericAddrSpaces

Summary:
We used to assume V->RAUW only modifies the operand list of V's user.
However, if V and V's user are Constants, RAUW may replace and invalidate V's
user entirely.

This patch fixes the above issue by letting the caller replace the
operand instead of calling RAUW on Constants.

Test Plan: @nested_const_expr and @rauw in access-non-generic.ll

Reviewers: broune, jholewinski

Reviewed By: broune, jholewinski

Subscribers: jholewinski, llvm-commits

Differential Revision: http://reviews.llvm.org/D10345

llvm-svn: 239435

1 files changed, 60 insertions, 54 deletions

diff --git a/llvm/lib/Target/NVPTX/NVPTXFavorNonGenericAddrSpaces.cpp b/llvm/lib/Target/NVPTX/NVPTXFavorNonGenericAddrSpaces.cpp
index cfff0019b8d..69a229e32f4 100644
--- a/llvm/lib/Target/NVPTX/NVPTXFavorNonGenericAddrSpaces.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXFavorNonGenericAddrSpaces.cpp
@@ -98,15 +98,14 @@ private:
   /// This reordering exposes to optimizeMemoryInstruction more
   /// optimization opportunities on loads and stores.
   ///
-  /// Returns true if this function succesfully hoists an eliminable
-  /// addrspacecast or V is already such an addrspacecast.
-  /// Transforms "gep (addrspacecast X), indices" into "addrspacecast (gep X,
-  /// indices)".
-  bool hoistAddrSpaceCastFrom(Value *V, int Depth = 0);
+  /// If this function succesfully hoists an eliminable addrspacecast or V is
+  /// already such an addrspacecast, it returns the transformed value (which is
+  /// guaranteed to be an addrspacecast); otherwise, it returns nullptr.
+  Value *hoistAddrSpaceCastFrom(Value *V, int Depth = 0);
   /// Helper function for GEPs.
-  bool hoistAddrSpaceCastFromGEP(GEPOperator *GEP, int Depth);
+  Value *hoistAddrSpaceCastFromGEP(GEPOperator *GEP, int Depth);
   /// Helper function for bitcasts.
-  bool hoistAddrSpaceCastFromBitCast(BitCastOperator *BC, int Depth);
+  Value *hoistAddrSpaceCastFromBitCast(BitCastOperator *BC, int Depth);
 };
 }
 
@@ -143,17 +142,19 @@ static bool isEliminableAddrSpaceCast(Value *V) {
           DestTy->getAddressSpace() == AddressSpace::ADDRESS_SPACE_GENERIC);
 }
 
-bool NVPTXFavorNonGenericAddrSpaces::hoistAddrSpaceCastFromGEP(GEPOperator *GEP,
-                                                               int Depth) {
-  if (!hoistAddrSpaceCastFrom(GEP->getPointerOperand(), Depth + 1))
-    return false;
+Value *NVPTXFavorNonGenericAddrSpaces::hoistAddrSpaceCastFromGEP(
+    GEPOperator *GEP, int Depth) {
+  Value *NewOperand =
+      hoistAddrSpaceCastFrom(GEP->getPointerOperand(), Depth + 1);
+  if (NewOperand == nullptr)
+    return nullptr;
 
-  // That hoistAddrSpaceCastFrom succeeds implies GEP's pointer operand is now
-  // an eliminable addrspacecast.
-  assert(isEliminableAddrSpaceCast(GEP->getPointerOperand()));
-  Operator *Cast = cast<Operator>(GEP->getPointerOperand());
+  // hoistAddrSpaceCastFrom returns an eliminable addrspacecast or nullptr.
+  assert(isEliminableAddrSpaceCast(NewOperand));
+  Operator *Cast = cast<Operator>(NewOperand);
 
   SmallVector<Value *, 8> Indices(GEP->idx_begin(), GEP->idx_end());
+  Value *NewASC;
   if (Instruction *GEPI = dyn_cast<Instruction>(GEP)) {
     // GEP = gep (addrspacecast X), indices
     // =>
@@ -163,30 +164,31 @@ bool NVPTXFavorNonGenericAddrSpaces::hoistAddrSpaceCastFromGEP(GEPOperator *GEP,
         GEP->getSourceElementType(), Cast->getOperand(0), Indices,
         "", GEPI);
     NewGEP->setIsInBounds(GEP->isInBounds());
-    Value *NewASC = new AddrSpaceCastInst(NewGEP, GEP->getType(), "", GEPI);
+    NewASC = new AddrSpaceCastInst(NewGEP, GEP->getType(), "", GEPI);
     NewASC->takeName(GEP);
+    // Without RAUWing GEP, the compiler would visit GEP again and emit
+    // redundant instructions. This is exercised in test @rauw in
+    // access-non-generic.ll.
     GEP->replaceAllUsesWith(NewASC);
   } else {
     // GEP is a constant expression.
     Constant *NewGEP = ConstantExpr::getGetElementPtr(
         GEP->getSourceElementType(), cast<Constant>(Cast->getOperand(0)),
         Indices, GEP->isInBounds());
-    GEP->replaceAllUsesWith(
-        ConstantExpr::getAddrSpaceCast(NewGEP, GEP->getType()));
+    NewASC = ConstantExpr::getAddrSpaceCast(NewGEP, GEP->getType());
   }
-
-  return true;
+  return NewASC;
 }
 
-bool NVPTXFavorNonGenericAddrSpaces::hoistAddrSpaceCastFromBitCast(
+Value *NVPTXFavorNonGenericAddrSpaces::hoistAddrSpaceCastFromBitCast(
     BitCastOperator *BC, int Depth) {
-  if (!hoistAddrSpaceCastFrom(BC->getOperand(0), Depth + 1))
-    return false;
+  Value *NewOperand = hoistAddrSpaceCastFrom(BC->getOperand(0), Depth + 1);
+  if (NewOperand == nullptr)
+    return nullptr;
 
-  // That hoistAddrSpaceCastFrom succeeds implies BC's source operand is now
-  // an eliminable addrspacecast.
-  assert(isEliminableAddrSpaceCast(BC->getOperand(0)));
-  Operator *Cast = cast<Operator>(BC->getOperand(0));
+  // hoistAddrSpaceCastFrom returns an eliminable addrspacecast or nullptr.
+  assert(isEliminableAddrSpaceCast(NewOperand));
+  Operator *Cast = cast<Operator>(NewOperand);
 
   // Cast  = addrspacecast Src
   // BC    = bitcast Cast
@@ -197,31 +199,34 @@ bool NVPTXFavorNonGenericAddrSpaces::hoistAddrSpaceCastFromBitCast(
   Type *TypeOfNewCast =
       PointerType::get(BC->getType()->getPointerElementType(),
                        Src->getType()->getPointerAddressSpace());
+  Value *NewBC;
   if (BitCastInst *BCI = dyn_cast<BitCastInst>(BC)) {
     Value *NewCast = new BitCastInst(Src, TypeOfNewCast, "", BCI);
-    Value *NewBC = new AddrSpaceCastInst(NewCast, BC->getType(), "", BCI);
+    NewBC = new AddrSpaceCastInst(NewCast, BC->getType(), "", BCI);
     NewBC->takeName(BC);
+    // Without RAUWing BC, the compiler would visit BC again and emit
+    // redundant instructions. This is exercised in test @rauw in
+    // access-non-generic.ll.
     BC->replaceAllUsesWith(NewBC);
   } else {
     // BC is a constant expression.
     Constant *NewCast =
         ConstantExpr::getBitCast(cast<Constant>(Src), TypeOfNewCast);
-    Constant *NewBC = ConstantExpr::getAddrSpaceCast(NewCast, BC->getType());
-    BC->replaceAllUsesWith(NewBC);
+    NewBC = ConstantExpr::getAddrSpaceCast(NewCast, BC->getType());
   }
-  return true;
+  return NewBC;
 }
 
-bool NVPTXFavorNonGenericAddrSpaces::hoistAddrSpaceCastFrom(Value *V,
-                                                            int Depth) {
-  // Returns true if V is already an eliminable addrspacecast.
+Value *NVPTXFavorNonGenericAddrSpaces::hoistAddrSpaceCastFrom(Value *V,
+                                                              int Depth) {
+  // Returns V if V is already an eliminable addrspacecast.
   if (isEliminableAddrSpaceCast(V))
-    return true;
+    return V;
 
   // Limit the depth to prevent this recursive function from running too long.
   const int MaxDepth = 20;
   if (Depth >= MaxDepth)
-    return false;
+    return nullptr;
 
   // If V is a GEP or bitcast, hoist the addrspacecast if any from its pointer
   // operand. This enables optimizeMemoryInstruction to shortcut addrspacecasts
@@ -232,28 +237,29 @@ bool NVPTXFavorNonGenericAddrSpaces::hoistAddrSpaceCastFrom(Value *V,
   if (BitCastOperator *BC = dyn_cast<BitCastOperator>(V))
     return hoistAddrSpaceCastFromBitCast(BC, Depth);
 
-  return false;
+  return nullptr;
 }
 
 bool NVPTXFavorNonGenericAddrSpaces::optimizeMemoryInstruction(Instruction *MI,
                                                                unsigned Idx) {
-  if (hoistAddrSpaceCastFrom(MI->getOperand(Idx))) {
-    // load/store (addrspacecast X) => load/store X if shortcutting the
-    // addrspacecast is valid and can improve performance.
-    //
-    // e.g.,
-    // %1 = addrspacecast float addrspace(3)* %0 to float*
-    // %2 = load float* %1
-    // ->
-    // %2 = load float addrspace(3)* %0
-    //
-    // Note: the addrspacecast can also be a constant expression.
-    assert(isEliminableAddrSpaceCast(MI->getOperand(Idx)));
-    Operator *ASC = dyn_cast<Operator>(MI->getOperand(Idx));
-    MI->setOperand(Idx, ASC->getOperand(0));
-    return true;
-  }
-  return false;
+  Value *NewOperand = hoistAddrSpaceCastFrom(MI->getOperand(Idx));
+  if (NewOperand == nullptr)
+    return false;
+
+  // load/store (addrspacecast X) => load/store X if shortcutting the
+  // addrspacecast is valid and can improve performance.
+  //
+  // e.g.,
+  // %1 = addrspacecast float addrspace(3)* %0 to float*
+  // %2 = load float* %1
+  // ->
+  // %2 = load float addrspace(3)* %0
+  //
+  // Note: the addrspacecast can also be a constant expression.
+  assert(isEliminableAddrSpaceCast(NewOperand));
+  Operator *ASC = dyn_cast<Operator>(NewOperand);
+  MI->setOperand(Idx, ASC->getOperand(0));
+  return true;
 }
 
 bool NVPTXFavorNonGenericAddrSpaces::runOnFunction(Function &F) {