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

[Robert Imschweiler via llvm-commits]

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

>From 107930bb7ac0c2a9867285a931042b707986e606 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 1/2] [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 54458201af0b3..d515d090f54e0 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"));

>From 28f70abab70ae1091894720cd779d8a1433d73dd Mon Sep 17 00:00:00 2001
From: Robert Imschweiler <robert.imschweiler at amd.com>
Date: Tue, 4 Nov 2025 03:16:48 -0600
Subject: [PATCH 2/2] always return true for now

---
 llvm/include/llvm/IR/DataLayout.h    | 4 +---
 llvm/unittests/IR/DataLayoutTest.cpp | 6 +++---
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/llvm/include/llvm/IR/DataLayout.h b/llvm/include/llvm/IR/DataLayout.h
index d515d090f54e0..7e6d2f9de506d 100644
--- a/llvm/include/llvm/IR/DataLayout.h
+++ b/llvm/include/llvm/IR/DataLayout.h
@@ -400,9 +400,7 @@ class DataLayout {
 
   /// Returns if the null pointer for this address space has an all-zero bit
   /// representation.
-  bool isNullPointerAllZeroes(unsigned AddrSpace) const {
-    return AddrSpace == 0;
-  }
+  bool isNullPointerAllZeroes(unsigned AddrSpace) const { return true; }
 
   /// Returns whether this address space has an "unstable" pointer
   /// representation. The bitwise pattern of such pointers is allowed to change
diff --git a/llvm/unittests/IR/DataLayoutTest.cpp b/llvm/unittests/IR/DataLayoutTest.cpp
index d5336a89c5859..e26c2aec6549d 100644
--- a/llvm/unittests/IR/DataLayoutTest.cpp
+++ b/llvm/unittests/IR/DataLayoutTest.cpp
@@ -702,11 +702,11 @@ TEST(DataLayout, NonIntegralHelpers) {
 
 TEST(DataLayoutTest, IsNullPointerAllZeroes) {
   EXPECT_TRUE(DataLayout("").isNullPointerAllZeroes(0));
-  EXPECT_FALSE(DataLayout("").isNullPointerAllZeroes(1));
+  EXPECT_TRUE(DataLayout("").isNullPointerAllZeroes(1));
   EXPECT_TRUE(DataLayout("p:32:32").isNullPointerAllZeroes(0));
-  EXPECT_FALSE(DataLayout("p:32:32").isNullPointerAllZeroes(1));
+  EXPECT_TRUE(DataLayout("p:32:32").isNullPointerAllZeroes(1));
   EXPECT_TRUE(DataLayout("p:64:64").isNullPointerAllZeroes(0));
-  EXPECT_FALSE(DataLayout("p:64:64").isNullPointerAllZeroes(1));
+  EXPECT_TRUE(DataLayout("p:64:64").isNullPointerAllZeroes(1));
 }
 
 TEST(DataLayoutTest, CopyAssignmentInvalidatesStructLayout) {