move to getNullPointerValue

Co-authored-by: Alexander Richardson <[email protected]>

Author: ro-i

llvm/include/llvm/IR/DataLayout.h

@@ -398,10 +398,14 @@ 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;
+  /// Return the bit value of the null pointer for the given address space.
+  std::optional<APInt> getNullPointerValue(unsigned AS) const {
+    // Address space zero is currently defined to always have an all-zero null
+    // pointer representation, the others are target-specific and will require a
+    // data layout property (work-in-progress).
+    if (AS == 0)
+      return APInt::getZero(getPointerSizeInBits(AS));
+    return std::nullopt;
   }
 
   /// Returns whether this address space has an "unstable" pointer

llvm/unittests/IR/DataLayoutTest.cpp

@@ -700,13 +700,13 @@ 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, GetNullPointerValue) {
+  EXPECT_EQ(DataLayout("").getNullPointerValue(0), APInt::getZero(64));
+  EXPECT_EQ(DataLayout("").getNullPointerValue(1), std::nullopt);
+  EXPECT_EQ(DataLayout("p:32:32").getNullPointerValue(0), APInt::getZero(32));
+  EXPECT_EQ(DataLayout("p:32:32").getNullPointerValue(1), std::nullopt);
+  EXPECT_EQ(DataLayout("p:64:64").getNullPointerValue(0), APInt::getZero(64));
+  EXPECT_EQ(DataLayout("p:64:64").getNullPointerValue(1), std::nullopt);
 }
 
 TEST(DataLayoutTest, CopyAssignmentInvalidatesStructLayout) {