[llvm] [APInt] Fix getAllOnes() with zero width (PR #112227)

[Nikita Popov via llvm-commits]

https://github.com/nikic created https://github.com/llvm/llvm-project/pull/112227

This makes sure that APInt::getAllOnes() keeps working after the APInt constructor assertions are enabled.

I'm relaxing the requirement for the signed case to either an all zeros or all ones integer. This is basically saying that we can interpret the zero-width integer as either positive or negative.

>From 0ab1fbf634153a6d62df4a1d68aafd49ff1e61e9 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Mon, 14 Oct 2024 17:28:21 +0200
Subject: [PATCH] [APInt] Fix getAllOnes() with zero width

This makes sure that APInt::getAllOnes() keeps working after
the APInt constructor assertions are enabled.

I'm relaxing the requirement for the signed case to either
an all zeros or all ones integer.
---
 llvm/include/llvm/ADT/APInt.h    | 21 ++++++++++++++-------
 llvm/unittests/ADT/APIntTest.cpp |  1 +
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/llvm/include/llvm/ADT/APInt.h b/llvm/include/llvm/ADT/APInt.h
index a42dae8887392d..63a138527b32e1 100644
--- a/llvm/include/llvm/ADT/APInt.h
+++ b/llvm/include/llvm/ADT/APInt.h
@@ -112,14 +112,21 @@ class [[nodiscard]] APInt {
         bool implicitTrunc = true)
       : BitWidth(numBits) {
     if (!implicitTrunc) {
-      if (BitWidth == 0) {
-        assert(val == 0 && "Value must be zero for 0-bit APInt");
-      } else if (isSigned) {
-        assert(llvm::isIntN(BitWidth, val) &&
-               "Value is not an N-bit signed value");
+      if (isSigned) {
+        if (BitWidth == 0) {
+          assert((val == 0 || val == uint64_t(-1)) &&
+                 "Value must be 0 or -1 for signed 0-bit APInt");
+        } else {
+          assert(llvm::isIntN(BitWidth, val) &&
+                 "Value is not an N-bit signed value");
+        }
       } else {
-        assert(llvm::isUIntN(BitWidth, val) &&
-               "Value is not an N-bit unsigned value");
+        if (BitWidth == 0) {
+          assert(val == 0 && "Value must be zero for unsigned 0-bit APInt");
+        } else {
+          assert(llvm::isUIntN(BitWidth, val) &&
+                 "Value is not an N-bit unsigned value");
+        }
       }
     }
     if (isSingleWord()) {
diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
index 7a9ac5562e7722..4d5553fcbd1e3f 100644
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -3423,6 +3423,7 @@ TEST(APIntTest, ZeroWidth) {
   EXPECT_EQ(0U, ZW.getBitWidth());
   EXPECT_EQ(0U, APInt(0, ArrayRef<uint64_t>({0, 1, 2})).getBitWidth());
   EXPECT_EQ(0U, APInt(0, "0", 10).getBitWidth());
+  EXPECT_EQ(0U, APInt::getAllOnes(0).getBitWidth());
 
   // Default constructor is single bit wide.
   EXPECT_EQ(1U, APInt().getBitWidth());