Check whether a pointer is non-null (isKnownNonNull) in isKnownNonZero.

This handles the case where we have an inbounds GEP with alloca as the pointer.
This fixes the regression in PR12750 and rdar://13286434.
Note that we can also fix this by handling some GEP cases in isKnownNonNull.

llvm-svn: 177321

llvm/lib/Analysis/ValueTracking.cpp

@@ -953,6 +953,8 @@ bool llvm::isKnownNonZero(Value *V, const DataLayout *TD, unsigned Depth) {
 
   // Check for pointer simplifications.
   if (V->getType()->isPointerTy()) {
+    if (isKnownNonNull(V))
+      return true; 
     if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
       if (isGEPKnownNonNull(GEP, TD, Depth))
         return true;

llvm/test/Transforms/InstSimplify/compare.ll

@@ -682,3 +682,14 @@ define zeroext i1 @external_compare(i32* noalias %x) {
   ; CHECK: external_compare
   ; CHECK: ret i1 %cmp
 }
+
+define i1 @alloca_gep(i64 %a, i64 %b) {
+; CHECK: @alloca_gep
+; We can prove this GEP is non-null because it is inbounds and the pointer
+; is non-null.
+  %strs = alloca [1000 x [1001 x i8]], align 16
+  %x = getelementptr inbounds [1000 x [1001 x i8]]* %strs, i64 0, i64 %a, i64 %b
+  %cmp = icmp eq i8* %x, null
+  ret i1 %cmp
+; CHECK-NEXT: ret i1 false
+}