[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 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 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 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"));

>From 9113b53de54d2c3f5f6ad9e9e7c0f8cc96231ed7 Mon Sep 17 00:00:00 2001
From: Robert Imschweiler <robert.imschweiler at amd.com>
Date: Mon, 27 Oct 2025 16:20:09 -0500
Subject: [PATCH 2/2] move to getNullPointerValue

Co-authored-by: Alexander Richardson <alexrichardson at google.com>
---
 llvm/include/llvm/IR/DataLayout.h    | 12 ++++++++----
 llvm/unittests/IR/DataLayoutTest.cpp | 14 +++++++-------
 2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/llvm/include/llvm/IR/DataLayout.h b/llvm/include/llvm/IR/DataLayout.h
index b8dcd6647f877..a2106dd7c4dd0 100644
--- a/llvm/include/llvm/IR/DataLayout.h
+++ b/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
diff --git a/llvm/unittests/IR/DataLayoutTest.cpp b/llvm/unittests/IR/DataLayoutTest.cpp
index d5336a89c5859..d82e31c6dca6c 100644
--- a/llvm/unittests/IR/DataLayoutTest.cpp
+++ b/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) {