[DataLayout] Add isNullPointerAllZeroes

Add a function to check for a given address space if its null pointer
has an all-zero bit representation.

Author: ro-i

llvm/include/llvm/IR/DataLayout.h

@@ -398,6 +398,12 @@ class DataLayout {
            PS.HasExternalState;
   }
 
+  /// Returns if the null pointer for this address space has an all-zero bit
+  /// representation.
+  bool isNullPointerAllZeroes(unsigned AddrSpace) const {
+    return AddrSpace == 0;
+  }
+
   /// Returns whether this address space has an "unstable" pointer
   /// representation. The bitwise pattern of such pointers is allowed to change
   /// in a target-specific way. For example, this could be used for copying

llvm/unittests/IR/DataLayoutTest.cpp

@@ -700,6 +700,15 @@ TEST(DataLayout, NonIntegralHelpers) {
   }
 }
 
+TEST(DataLayoutTest, IsNullPointerAllZeroes) {
+  EXPECT_TRUE(DataLayout("").isNullPointerAllZeroes(0));
+  EXPECT_FALSE(DataLayout("").isNullPointerAllZeroes(1));
+  EXPECT_TRUE(DataLayout("p:32:32").isNullPointerAllZeroes(0));
+  EXPECT_FALSE(DataLayout("p:32:32").isNullPointerAllZeroes(1));
+  EXPECT_TRUE(DataLayout("p:64:64").isNullPointerAllZeroes(0));
+  EXPECT_FALSE(DataLayout("p:64:64").isNullPointerAllZeroes(1));
+}
+
 TEST(DataLayoutTest, CopyAssignmentInvalidatesStructLayout) {
   DataLayout DL1 = cantFail(DataLayout::parse("p:32:32"));
   DataLayout DL2 = cantFail(DataLayout::parse("p:64:64"));