From 3637aff1ea50561a331f53c236f504254fc7cf03 Mon Sep 17 00:00:00 2001
From: Raphael Isemann <teemperor@gmail.com>
Date: Wed, 10 Jun 2020 16:35:42 +0200
Subject: [PATCH] ADT: Fix that APSInt's string constructor claims it requires
 5 bits to store a zero

Summary:

When constructing an APSInt from a string, the constructor doesn't correctly
truncate the bit width of the result if the passed in string was "0" (or any
alternative way to express 0 like "-0" or "000"). Instead of 1 (which is the
smallest allowed bit width) it returns an APSInt with a bit width of 5.

The reason is that the constructor checks that it never truncates the result to
the invalid bit width of 0, so when it calculates that storing a "0" doesn't
require any bits it just keeps the original overestimated bit width (which
happens to be 5).

This patch just sets the bit width of the result to 1 if the required bit width
is 0.

Reviewers: arphaman, dexonsmith

Reviewed By: dexonsmith

Subscribers: hiraditya, dexonsmith, JDevlieghere, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D81329
---
 lib/Support/APSInt.cpp       |  8 ++++----
 unittests/ADT/APSIntTest.cpp | 23 +++++++++++++++++++++++
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/lib/Support/APSInt.cpp b/lib/Support/APSInt.cpp
index 6805e06df33..b65b6824eaf 100644
--- a/lib/Support/APSInt.cpp
+++ b/lib/Support/APSInt.cpp
@@ -26,14 +26,14 @@ APSInt::APSInt(StringRef Str) {
   APInt Tmp(NumBits, Str, /*radix=*/10);
   if (Str[0] == '-') {
     unsigned MinBits = Tmp.getMinSignedBits();
-    if (MinBits > 0 && MinBits < NumBits)
-      Tmp = Tmp.trunc(MinBits);
+    if (MinBits < NumBits)
+      Tmp = Tmp.trunc(std::max<unsigned>(1, MinBits));
     *this = APSInt(Tmp, /*isUnsigned=*/false);
     return;
   }
   unsigned ActiveBits = Tmp.getActiveBits();
-  if (ActiveBits > 0 && ActiveBits < NumBits)
-    Tmp = Tmp.trunc(ActiveBits);
+  if (ActiveBits < NumBits)
+    Tmp = Tmp.trunc(std::max<unsigned>(1, ActiveBits));
   *this = APSInt(Tmp, /*isUnsigned=*/true);
 }
 
diff --git a/unittests/ADT/APSIntTest.cpp b/unittests/ADT/APSIntTest.cpp
index 9045f3e48f7..932f54c19f1 100644
--- a/unittests/ADT/APSIntTest.cpp
+++ b/unittests/ADT/APSIntTest.cpp
@@ -150,6 +150,29 @@ TEST(APSIntTest, FromString) {
   EXPECT_EQ(APSInt("-1234").getExtValue(), -1234);
 }
 
+TEST(APSIntTest, FromStringBitWidth) {
+  EXPECT_EQ(APSInt("0").getBitWidth(), 1U);
+  EXPECT_EQ(APSInt("000").getBitWidth(), 1U);
+  EXPECT_EQ(APSInt("1").getBitWidth(), 1U);
+  EXPECT_EQ(APSInt("2").getBitWidth(), 2U);
+  EXPECT_EQ(APSInt("3").getBitWidth(), 2U);
+  EXPECT_EQ(APSInt("003").getBitWidth(), 2U);
+  EXPECT_EQ(APSInt("15").getBitWidth(), 4U);
+  EXPECT_EQ(APSInt("16").getBitWidth(), 5U);
+  EXPECT_EQ(APSInt("17").getBitWidth(), 5U);
+
+  EXPECT_EQ(APSInt("-0").getBitWidth(), 1U);
+  EXPECT_EQ(APSInt("-000").getBitWidth(), 1U);
+  EXPECT_EQ(APSInt("-1").getBitWidth(), 1U);
+  EXPECT_EQ(APSInt("-2").getBitWidth(), 2U);
+  EXPECT_EQ(APSInt("-3").getBitWidth(), 3U);
+  EXPECT_EQ(APSInt("-003").getBitWidth(), 3U);
+  EXPECT_EQ(APSInt("-5").getBitWidth(), 4U);
+  EXPECT_EQ(APSInt("-15").getBitWidth(), 5U);
+  EXPECT_EQ(APSInt("-16").getBitWidth(), 5U);
+  EXPECT_EQ(APSInt("-17").getBitWidth(), 6U);
+}
+
 #if defined(GTEST_HAS_DEATH_TEST) && !defined(NDEBUG)
 
 TEST(APSIntTest, StringDeath) {