[PATCH] D85524: [Loads] Add canReplacePointersIfEqual helper.

[Florian Hahn via Phabricator via llvm-commits]

fhahn updated this revision to Diff 285350.
fhahn added a comment.

Use isDereferenceableAndAlignedPointer directly and pass size of 1.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D85524/new/

https://reviews.llvm.org/D85524

Files:
  llvm/include/llvm/Analysis/Loads.h
  llvm/lib/Analysis/Loads.cpp


Index: llvm/lib/Analysis/Loads.cpp
===================================================================
--- llvm/lib/Analysis/Loads.cpp
+++ llvm/lib/Analysis/Loads.cpp
@@ -503,3 +503,23 @@
   // block.
   return nullptr;
 }
+
+bool llvm::canReplacePointersIfEqual(Value *A, Value *B, const DataLayout &DL,
+                                     Instruction *CtxI) {
+  Type *Ty = A->getType();
+  assert(Ty == B->getType() && Ty->isPointerTy() &&
+         "values must have matching pointer types");
+
+  // NOTE: The checks in the function are incomplete and currently miss illegal
+  // cases! The current implementation is a starting point and the
+  // implementation should be made stricter over time.
+  if (auto *C = dyn_cast<Constant>(B)) {
+    // Do not allow replacing a pointer with a constant pointer, unless it is
+    // either null or at least one byte is dereferenceable.
+    APInt OneByte(DL.getPointerTypeSizeInBits(A->getType()), 1);
+    return C->isNullValue() ||
+           isDereferenceableAndAlignedPointer(B, Align(1), OneByte, DL, CtxI);
+  }
+
+  return true;
+}
Index: llvm/include/llvm/Analysis/Loads.h
===================================================================
--- llvm/include/llvm/Analysis/Loads.h
+++ llvm/include/llvm/Analysis/Loads.h
@@ -155,6 +155,14 @@
                                  BasicBlock::iterator &ScanFrom,
                                  unsigned MaxInstsToScan, AAResults *AA,
                                  bool *IsLoadCSE, unsigned *NumScanedInst);
+
+/// Returns true if a pointer value \p A can be replace with another pointer
+/// value \B if they are deemed equal through some means (e.g. information from
+/// conditions).
+//  NOTE: the current implementations is incomplete and unsound. It does not
+//  reject all invalid cases yet, but will be made stricter in the future.
+bool canReplacePointersIfEqual(Value *A, Value *B, const DataLayout &DL,
+                               Instruction *CtxI);
 }
 
 #endif


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