[PATCH] D85522: [Loads] Globals are dereferenceable, if offset + size <= sizeof(global).

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: nlopes, efriedma, hfinkel, aqjune.
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Currently we fail to determine whether pointers to globals are
dereferenceable. Unless I am missing something, we can treat constant
expression GEPs as dereferenceable, if all the dereferenced bits fall
within the global's size.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D85522

Files:
  llvm/lib/Analysis/Loads.cpp


Index: llvm/lib/Analysis/Loads.cpp
===================================================================
--- llvm/lib/Analysis/Loads.cpp
+++ llvm/lib/Analysis/Loads.cpp
@@ -85,6 +85,15 @@
              .isMinValue())
       return false;
 
+    // A pointer to a global value is dereferenceable  if all dereferenced bits
+    // are within the global's size.
+    if (auto *GV = dyn_cast<GlobalValue>(Base)) {
+      if (((Offset + Size.sextOrTrunc(Offset.getBitWidth())) * 8)
+              .ule(
+                  DL.getTypeSizeInBits(GV->getType()->getPointerElementType())))
+        return true;
+    }
+
     // If the base pointer is dereferenceable for Offset+Size bytes, then the
     // GEP (== Base + Offset) is dereferenceable for Size bytes.  If the base
     // pointer is aligned to Align bytes, and the Offset is divisible by Align


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