[ValueTracking] Pointer is known nonnull after load/store

If the pointer was loaded/stored before the null check, the check
is redundant and can be removed. For now the optimizers do not
remove the nullptr check, see https://gcc.godbolt.org/z/H2r5GG.
The patch allows to use more nonnull constraints. Also, it found
one more optimization in some PowerPC test. This is my first llvm
review, I am free to any comments.

Differential Revision: https://reviews.llvm.org/D71177

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index e35b235b0bb..0d15187f575 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1943,6 +1943,15 @@ static bool isKnownNonNullFromDominatingCondition(const Value *V,
               Arg.hasNonNullAttr() && DT->dominates(CS.getInstruction(), CtxI))
             return true;
 
+    // If the value is used as a load/store, then the pointer must be non null.
+    if (V == getLoadStorePointerOperand(U)) {
+      const Instruction *I = cast<Instruction>(U);
+      if (!NullPointerIsDefined(I->getFunction(),
+                                V->getType()->getPointerAddressSpace()) &&
+          DT->dominates(I, CtxI))
+        return true;
+    }
+
     // Consider only compare instructions uniquely controlling a branch
     CmpInst::Predicate Pred;
     if (!match(const_cast<User *>(U),