[llvm] f60e319 - ADT: Fix that APSInt's string constructor claims it requires 5 bits to store a zero

[Raphael Isemann via llvm-commits]

Author: Raphael Isemann
Date: 2020-06-10T16:36:33+02:00
New Revision: f60e319419b848b5789d4713de38df381e4fe7b4

URL: https://github.com/llvm/llvm-project/commit/f60e319419b848b5789d4713de38df381e4fe7b4
DIFF: https://github.com/llvm/llvm-project/commit/f60e319419b848b5789d4713de38df381e4fe7b4.diff

LOG: 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

Added: 
    

Modified: 
    llvm/lib/Support/APSInt.cpp
    llvm/unittests/ADT/APSIntTest.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Support/APSInt.cpp b/llvm/lib/Support/APSInt.cpp
index 6805e06df333..b65b6824eaf8 100644
--- a/llvm/lib/Support/APSInt.cpp
+++ b/llvm/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/llvm/unittests/ADT/APSIntTest.cpp b/llvm/unittests/ADT/APSIntTest.cpp
index 9045f3e48f7d..932f54c19f18 100644
--- a/llvm/unittests/ADT/APSIntTest.cpp
+++ b/llvm/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) {