[PATCH] D133426: [LICM][LSR] Address a couple of special cases involving NULL.

[Stefan Pintilie via Phabricator via llvm-commits]

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While looking at tests with opaque pointers it was noticed that LICM and
Loop Strength reduction behave differently in cases when a pointer is NULL.

This patch adds special cases to deal with NULL.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D133426

Files:
  llvm/lib/Transforms/Scalar/LICM.cpp
  llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp


Index: llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -3471,9 +3471,14 @@
       if (const Instruction *Inst = dyn_cast<Instruction>(V)) {
         // Look for instructions defined outside the loop.
         if (L->contains(Inst)) continue;
-      } else if (isa<UndefValue>(V))
+      } else if (isa<UndefValue>(V)) {
         // Undef doesn't have a live range, so it doesn't matter.
         continue;
+      } else if (const Constant *Const = dyn_cast<Constant>(V)) {
+        // NULL values don't really have a live range. They are just NULL.
+        if (Const->isNullValue())
+          continue;
+      }
       for (const Use &U : V->uses()) {
         const Instruction *UserInst = dyn_cast<Instruction>(U.getUser());
         // Ignore non-instructions.
Index: llvm/lib/Transforms/Scalar/LICM.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LICM.cpp
+++ llvm/lib/Transforms/Scalar/LICM.cpp
@@ -2092,9 +2092,14 @@
               Store->getPointerOperand(), Store->getValueOperand()->getType(),
               Store->getAlign(), MDL, Preheader->getTerminator(), DT, TLI);
         }
-      } else
-        return false; // Not a load or store.
-
+      } else {
+        // Uses of null that are not loads or stores can be ignored.
+        if (const Constant *Const = dyn_cast<Constant>(ASIV)) {
+          if (Const->isNullValue())
+            continue;
+        }
+        return false; // Not a load or store and not null.
+      }
       if (!AccessTy)
         AccessTy = getLoadStoreType(UI);
       else if (AccessTy != getLoadStoreType(UI))


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