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

2 files changed, 13 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index 53e9f49a571..542ff709d47 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/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/llvm/lib/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index cf32a66c901..9e0a43ce1e3 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/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);
 }