[llvm] [DataLayout] Add isNullPointerAllZeroes (PR #165314)

[Robert Imschweiler via llvm-commits]

https://github.com/ro-i created https://github.com/llvm/llvm-project/pull/165314

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

---------

See https://github.com/llvm/llvm-project/pull/140802#discussion_r2466373958
Maybe something like `getNullPointerValue` would be more useful, but would depend on https://github.com/llvm/llvm-project/pull/131557 and the open questions around it.

>From 1721831722e6614c4b7be6b5b66ab4131776facd Mon Sep 17 00:00:00 2001
From: Robert Imschweiler <robert.imschweiler at amd.com>
Date: Mon, 27 Oct 2025 15:41:10 -0500
Subject: [PATCH] [DataLayout] Add isNullPointerAllZeroes

Add a function to check for a given address space if its null pointer
has an all-zero bit representation.
---
 llvm/include/llvm/IR/DataLayout.h    | 6 ++++++
 llvm/unittests/IR/DataLayoutTest.cpp | 9 +++++++++
 2 files changed, 15 insertions(+)

diff --git a/llvm/include/llvm/IR/DataLayout.h b/llvm/include/llvm/IR/DataLayout.h
index 56fc749838ef9..b8dcd6647f877 100644
--- a/llvm/include/llvm/IR/DataLayout.h
+++ b/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
diff --git a/llvm/unittests/IR/DataLayoutTest.cpp b/llvm/unittests/IR/DataLayoutTest.cpp
index 9ca88141ca0eb..d5336a89c5859 100644
--- a/llvm/unittests/IR/DataLayoutTest.cpp
+++ b/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"));