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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@362545 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/IR/Value.h b/include/llvm/IR/Value.h
index d0de008db265f7c1ce1fa34ab9a1213430c1e945..3f8caa668e51b0703bea4e351cdd59fd1c6b960c 100644 (file)
--- a/include/llvm/IR/Value.h
+++ b/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.
   ///

diff --git a/lib/Analysis/LazyValueInfo.cpp b/lib/Analysis/LazyValueInfo.cpp
index 53e9f49a5711dd33aa4b912fcc9b418ed4af25d1..542ff709d4755cac5e68af76dfd29a07f79b0c23 100644 (file)
--- a/lib/Analysis/LazyValueInfo.cpp
+++ b/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)

diff --git a/lib/IR/Value.cpp b/lib/IR/Value.cpp
index cf32a66c90143c6f86e1752a838386349898caae..9e0a43ce1e30a634202a002c02be864ca6b9d001 100644 (file)
--- a/lib/IR/Value.cpp
+++ b/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);
 }