ADT: Add a string APSInt constructor.

This commit moves the APSInt initialization code that's used by
the LLLexer class into a new APSInt constructor that constructs
APSInts from strings.

This change is useful for MIR Serialization, as it would allow
the MILexer class to use the same APSInt initialization as 
LLexer when parsing immediate machine operands.

llvm-svn: 240436

llvm/include/llvm/ADT/APSInt.h

@@ -33,6 +33,15 @@ public:
   explicit APSInt(APInt I, bool isUnsigned = true)
    : APInt(std::move(I)), IsUnsigned(isUnsigned) {}
 
+  /// Construct an APSInt from a string representation.
+  ///
+  /// This constructor interprets the string \p Str using the radix of 10.
+  /// The interpretation stops at the end of the string. The bit width of the
+  /// constructed APSInt is determined automatically.
+  ///
+  /// \param Str the string to be interpreted.
+  explicit APSInt(StringRef Str);
+
   APSInt &operator=(APInt RHS) {
     // Retain our current sign.
     APInt::operator=(std::move(RHS));

llvm/lib/AsmParser/LLLexer.cpp

@@ -903,20 +903,7 @@ lltok::Kind LLLexer::LexDigitOrNegative() {
   if (CurPtr[0] != '.') {
     if (TokStart[0] == '0' && TokStart[1] == 'x')
       return Lex0x();
-    unsigned Len = CurPtr-TokStart;
-    uint32_t numBits = ((Len * 64) / 19) + 2;
-    APInt Tmp(numBits, StringRef(TokStart, Len), 10);
-    if (TokStart[0] == '-') {
-      uint32_t minBits = Tmp.getMinSignedBits();
-      if (minBits > 0 && minBits < numBits)
-        Tmp = Tmp.trunc(minBits);
-      APSIntVal = APSInt(Tmp, false);
-    } else {
-      uint32_t activeBits = Tmp.getActiveBits();
-      if (activeBits > 0 && activeBits < numBits)
-        Tmp = Tmp.trunc(activeBits);
-      APSIntVal = APSInt(Tmp, true);
-    }
+    APSIntVal = APSInt(StringRef(TokStart, CurPtr - TokStart));
     return lltok::APSInt;
   }
 

llvm/lib/Support/APSInt.cpp

@@ -17,6 +17,25 @@
 
 using namespace llvm;
 
+APSInt::APSInt(StringRef Str) {
+  assert(!Str.empty() && "Invalid string length");
+
+  // (Over-)estimate the required number of bits.
+  unsigned NumBits = ((Str.size() * 64) / 19) + 2;
+  APInt Tmp(NumBits, Str, /*Radix=*/10);
+  if (Str[0] == '-') {
+    unsigned MinBits = Tmp.getMinSignedBits();
+    if (MinBits > 0 && MinBits < NumBits)
+      Tmp = Tmp.trunc(MinBits);
+    *this = APSInt(Tmp, /*IsUnsigned=*/false);
+    return;
+  }
+  unsigned ActiveBits = Tmp.getActiveBits();
+  if (ActiveBits > 0 && ActiveBits < NumBits)
+    Tmp = Tmp.trunc(ActiveBits);
+  *this = APSInt(Tmp, /*IsUnsigned=*/true);
+}
+
 void APSInt::Profile(FoldingSetNodeID& ID) const {
   ID.AddInteger((unsigned) (IsUnsigned ? 1 : 0));
   APInt::Profile(ID);

llvm/unittests/ADT/APSIntTest.cpp

@@ -143,4 +143,23 @@ TEST(APSIntTest, compareValues) {
   EXPECT_TRUE(APSInt::compareValues(U(8), S(-7).trunc(32)) > 0);
 }
 
+TEST(APSIntTest, FromString) {
+  EXPECT_EQ(APSInt("1").getExtValue(), 1);
+  EXPECT_EQ(APSInt("-1").getExtValue(), -1);
+  EXPECT_EQ(APSInt("0").getExtValue(), 0);
+  EXPECT_EQ(APSInt("56789").getExtValue(), 56789);
+  EXPECT_EQ(APSInt("-1234").getExtValue(), -1234);
 }
+
+#ifdef GTEST_HAS_DEATH_TEST
+#ifndef NDEBUG
+
+TEST(APSIntTest, StringDeath) {
+  EXPECT_DEATH(APSInt(""), "Invalid string length");
+  EXPECT_DEATH(APSInt("1a"), "Invalid character in digit string");
+}
+
+#endif
+#endif
+
+} // end anonymous namespace