Introduce Value::stripPointerCastsSameRepresentation

This patch allows current users of Value::stripPointerCasts() to force
the result of the function to have the same representation as the value
it was called on. This is useful in various cases, e.g., (non-)null
checks.

In this patch only a single call site was adjusted to fix an existing
misuse that would cause nonnull where they may be wrong. Uses in
attribute deduction and other areas, e.g., D60047, are to be expected.

For a discussion on this topic, please see [0].

[0] http://lists.llvm.org/pipermail/llvm-dev/2018-December/128423.html

Reviewers: hfinkel, arsenm, reames

Subscribers: wdng, hiraditya, bollu, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61607

llvm-svn: 362545

include/llvm/IR/Value.h

@@ -493,7 +493,7 @@ public:
   /// swifterror attribute.
   bool isSwiftError() const;
 
-  /// Strip off pointer casts, all-zero GEPs, and aliases.
+  /// Strip off pointer casts, all-zero GEPs, address space casts, and aliases.
   ///
   /// Returns the original uncasted value.  If this is called on a non-pointer
   /// value, it returns 'this'.
@@ -503,6 +503,17 @@ public:
                          static_cast<const Value *>(this)->stripPointerCasts());
   }
 
+  /// Strip off pointer casts, all-zero GEPs, address space casts, and aliases
+  /// but ensures the representation of the result stays the same.
+  ///
+  /// Returns the original uncasted value with the same representation. If this
+  /// is called on a non-pointer value, it returns 'this'.
+  const Value *stripPointerCastsSameRepresentation() const;
+  Value *stripPointerCastsSameRepresentation() {
+    return const_cast<Value *>(static_cast<const Value *>(this)
+                                   ->stripPointerCastsSameRepresentation());
+  }
+
   /// Strip off pointer casts, all-zero GEPs, aliases and invariant group
   /// info.
   ///

lib/Analysis/LazyValueInfo.cpp

@@ -1803,7 +1803,7 @@ LazyValueInfo::getPredicateAt(unsigned Pred, Value *V, Constant *C,
   // through would still be correct.
   const DataLayout &DL = CxtI->getModule()->getDataLayout();
   if (V->getType()->isPointerTy() && C->isNullValue() &&
-      isKnownNonZero(V->stripPointerCasts(), DL)) {
+      isKnownNonZero(V->stripPointerCastsSameRepresentation(), DL)) {
     if (Pred == ICmpInst::ICMP_EQ)
       return LazyValueInfo::False;
     else if (Pred == ICmpInst::ICMP_NE)

lib/IR/Value.cpp

@@ -460,6 +460,7 @@ namespace {
 enum PointerStripKind {
   PSK_ZeroIndices,
   PSK_ZeroIndicesAndAliases,
+  PSK_ZeroIndicesAndAliasesSameRepresentation,
   PSK_ZeroIndicesAndAliasesAndInvariantGroups,
   PSK_InBoundsConstantIndices,
   PSK_InBounds
@@ -479,6 +480,7 @@ static const Value *stripPointerCastsAndOffsets(const Value *V) {
     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
       switch (StripKind) {
       case PSK_ZeroIndicesAndAliases:
+      case PSK_ZeroIndicesAndAliasesSameRepresentation:
       case PSK_ZeroIndicesAndAliasesAndInvariantGroups:
       case PSK_ZeroIndices:
         if (!GEP->hasAllZeroIndices())
@@ -494,8 +496,12 @@ static const Value *stripPointerCastsAndOffsets(const Value *V) {
         break;
       }
       V = GEP->getPointerOperand();
-    } else if (Operator::getOpcode(V) == Instruction::BitCast ||
+    } else if (Operator::getOpcode(V) == Instruction::BitCast) {
+      V = cast<Operator>(V)->getOperand(0);
+    } else if (StripKind != PSK_ZeroIndicesAndAliasesSameRepresentation &&
                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
+      // TODO: If we know an address space cast will not change the
+      //       representation we could look through it here as well.
       V = cast<Operator>(V)->getOperand(0);
     } else if (auto *GA = dyn_cast<GlobalAlias>(V)) {
       if (StripKind == PSK_ZeroIndices || GA->isInterposable())
@@ -530,6 +536,11 @@ const Value *Value::stripPointerCasts() const {
   return stripPointerCastsAndOffsets<PSK_ZeroIndicesAndAliases>(this);
 }
 
+const Value *Value::stripPointerCastsSameRepresentation() const {
+  return stripPointerCastsAndOffsets<
+      PSK_ZeroIndicesAndAliasesSameRepresentation>(this);
+}
+
 const Value *Value::stripPointerCastsNoFollowAliases() const {
   return stripPointerCastsAndOffsets<PSK_ZeroIndices>(this);
 }