[APInt] Add ashrInPlace method and implement ashr using it. Also fix a bug in the...

For single word, shift by BitWidth was always returning 0, but for multiword it was based on original sign. Now single word matches multi word.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301094 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/ADT/APInt.h b/include/llvm/ADT/APInt.h
index c697402341fca04ecb6c105b70198d703777b633..022cfc985e117efef781af8811c5d1b53934318a 100644 (file)
--- a/include/llvm/ADT/APInt.h
+++ b/include/llvm/ADT/APInt.h
@@ -198,6 +198,9 @@ private:
   /// out-of-line slow case for lshr.
   void lshrSlowCase(unsigned ShiftAmt);
 
+  /// out-of-line slow case for ashr.
+  void ashrSlowCase(unsigned ShiftAmt);
+
   /// out-of-line slow case for operator=
   void AssignSlowCase(const APInt &RHS);
 
@@ -898,7 +901,26 @@ public:
   /// \brief Arithmetic right-shift function.
   ///
   /// Arithmetic right-shift this APInt by shiftAmt.
-  APInt ashr(unsigned shiftAmt) const;
+  APInt ashr(unsigned ShiftAmt) const {
+    APInt R(*this);
+    R.ashrInPlace(ShiftAmt);
+    return R;
+  }
+
+  /// Arithmetic right-shift this APInt by ShiftAmt in place.
+  void ashrInPlace(unsigned ShiftAmt) {
+    assert(ShiftAmt <= BitWidth && "Invalid shift amount");
+    if (isSingleWord()) {
+      int64_t SExtVAL = SignExtend64(VAL, BitWidth);
+      if (ShiftAmt == BitWidth)
+        VAL = SExtVAL >> (APINT_BITS_PER_WORD - 1); // undefined
+      else
+        VAL = SExtVAL >> ShiftAmt;
+      clearUnusedBits();
+      return;
+    }
+    ashrSlowCase(ShiftAmt);
+  }
 
   /// \brief Logical right-shift function.
   ///
@@ -940,7 +962,14 @@ public:
   /// \brief Arithmetic right-shift function.
   ///
   /// Arithmetic right-shift this APInt by shiftAmt.
-  APInt ashr(const APInt &shiftAmt) const;
+  APInt ashr(const APInt &ShiftAmt) const {
+    APInt R(*this);
+    R.ashrInPlace(ShiftAmt);
+    return R;
+  }
+
+  /// Arithmetic right-shift this APInt by shiftAmt in place.
+  void ashrInPlace(const APInt &shiftAmt);
 
   /// \brief Logical right-shift function.
   ///

diff --git a/include/llvm/ADT/APSInt.h b/include/llvm/ADT/APSInt.h
index 650d276fdb59e50bf1b4d7102acc702f6d169ff7..dabbf3314bd022e33d7e8aa35f94683e41d91725 100644 (file)
--- a/include/llvm/ADT/APSInt.h
+++ b/include/llvm/ADT/APSInt.h
@@ -128,7 +128,7 @@ public:
     if (IsUnsigned)
       lshrInPlace(Amt);
     else
-      *this = *this >> Amt;
+      ashrInPlace(Amt);
     return *this;
   }
 

diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp
index 9bb364af27918193f15ba5d9935bafe6891fbf2f..c72e3bf9872c1788e806adb4328e627949d593f1 100644 (file)
--- a/lib/Support/APInt.cpp
+++ b/lib/Support/APInt.cpp
@@ -1029,89 +1029,42 @@ APInt APInt::sextOrSelf(unsigned width) const {
 
 /// Arithmetic right-shift this APInt by shiftAmt.
 /// @brief Arithmetic right-shift function.
-APInt APInt::ashr(const APInt &shiftAmt) const {
-  return ashr((unsigned)shiftAmt.getLimitedValue(BitWidth));
+void APInt::ashrInPlace(const APInt &shiftAmt) {
+  ashrInPlace((unsigned)shiftAmt.getLimitedValue(BitWidth));
 }
 
 /// Arithmetic right-shift this APInt by shiftAmt.
 /// @brief Arithmetic right-shift function.
-APInt APInt::ashr(unsigned shiftAmt) const {
-  assert(shiftAmt <= BitWidth && "Invalid shift amount");
-  // Handle a degenerate case
-  if (shiftAmt == 0)
-    return *this;
+void APInt::ashrSlowCase(unsigned ShiftAmt) {
+  // Don't bother performing a no-op shift.
+  if (!ShiftAmt)
+    return;
 
-  // Handle single word shifts with built-in ashr
-  if (isSingleWord()) {
-    if (shiftAmt == BitWidth)
-      return APInt(BitWidth, 0); // undefined
-    return APInt(BitWidth, SignExtend64(VAL, BitWidth) >> shiftAmt);
-  }
+  bool Negative = isNegative();
 
-  // If all the bits were shifted out, the result is, technically, undefined.
-  // We return -1 if it was negative, 0 otherwise. We check this early to avoid
-  // issues in the algorithm below.
-  if (shiftAmt == BitWidth) {
-    if (isNegative())
-      return APInt(BitWidth, WORD_MAX, true);
-    else
-      return APInt(BitWidth, 0);
-  }
-
-  // Create some space for the result.
-  uint64_t * val = new uint64_t[getNumWords()];
-
-  // Compute some values needed by the following shift algorithms
-  unsigned wordShift = shiftAmt % APINT_BITS_PER_WORD; // bits to shift per word
-  unsigned offset = shiftAmt / APINT_BITS_PER_WORD; // word offset for shift
-  unsigned breakWord = getNumWords() - 1 - offset; // last word affected
-  unsigned bitsInWord = whichBit(BitWidth); // how many bits in last word?
-  if (bitsInWord == 0)
-    bitsInWord = APINT_BITS_PER_WORD;
-
-  // If we are shifting whole words, just move whole words
-  if (wordShift == 0) {
-    // Move the words containing significant bits
-    for (unsigned i = 0; i <= breakWord; ++i)
-      val[i] = pVal[i+offset]; // move whole word
-
-    // Adjust the top significant word for sign bit fill, if negative
-    if (isNegative())
-      if (bitsInWord < APINT_BITS_PER_WORD)
-        val[breakWord] |= WORD_MAX << bitsInWord; // set high bits
-  } else {
-    // Shift the low order words
-    for (unsigned i = 0; i < breakWord; ++i) {
-      // This combines the shifted corresponding word with the low bits from
-      // the next word (shifted into this word's high bits).
-      val[i] = (pVal[i+offset] >> wordShift) |
-               (pVal[i+offset+1] << (APINT_BITS_PER_WORD - wordShift));
-    }
+  // WordShift is the inter-part shift; BitShift is is intra-part shift.
+  unsigned Words = getNumWords();
+  unsigned WordShift = std::min(ShiftAmt / APINT_BITS_PER_WORD, Words);
+  unsigned BitShift = ShiftAmt % APINT_BITS_PER_WORD;
 
-    // Shift the break word. In this case there are no bits from the next word
-    // to include in this word.
-    val[breakWord] = pVal[breakWord+offset] >> wordShift;
-
-    // Deal with sign extension in the break word, and possibly the word before
-    // it.
-    if (isNegative()) {
-      if (wordShift > bitsInWord) {
-        if (breakWord > 0)
-          val[breakWord-1] |=
-            WORD_MAX << (APINT_BITS_PER_WORD - (wordShift - bitsInWord));
-        val[breakWord] |= WORD_MAX;
-      } else
-        val[breakWord] |= WORD_MAX << (bitsInWord - wordShift);
+  unsigned WordsToMove = Words - WordShift;
+  // Fastpath for moving by whole words.
+  if (BitShift == 0) {
+    std::memmove(pVal, pVal + WordShift, WordsToMove * APINT_WORD_SIZE);
+  } else {
+    for (unsigned i = 0; i != WordsToMove; ++i) {
+      pVal[i] = pVal[i + WordShift] >> BitShift;
+      if (i + 1 != WordsToMove)
+        pVal[i] |= pVal[i + WordShift + 1] << (APINT_BITS_PER_WORD - BitShift);
+      else if (Negative)
+        pVal[i] |= WORD_MAX << (APINT_BITS_PER_WORD - BitShift);
     }
   }
 
-  // Remaining words are 0 or -1, just assign them.
-  uint64_t fillValue = (isNegative() ? WORD_MAX : 0);
-  for (unsigned i = breakWord+1; i < getNumWords(); ++i)
-    val[i] = fillValue;
-  APInt Result(val, BitWidth);
-  Result.clearUnusedBits();
-  return Result;
+  // Fill in the remainder based on the original sign.
+  std::memset(pVal + WordsToMove, Negative ? -1 : 0,
+              WordShift * APINT_WORD_SIZE);
+  clearUnusedBits();
 }
 
 /// Logical right-shift this APInt by shiftAmt.

diff --git a/unittests/ADT/APIntTest.cpp b/unittests/ADT/APIntTest.cpp
index 5d3afe9a159f39b99a4a420175fe693da90008a6..6b889bf2dfda39a7a75889c1c29fb23328ce5839 100644 (file)
--- a/unittests/ADT/APIntTest.cpp
+++ b/unittests/ADT/APIntTest.cpp
@@ -288,7 +288,7 @@ TEST(APIntTest, i1) {
   EXPECT_EQ(zero, one.shl(1));
   EXPECT_EQ(one, one.shl(0));
   EXPECT_EQ(zero, one.lshr(1));
-  EXPECT_EQ(zero, one.ashr(1));
+  EXPECT_EQ(one, one.ashr(1));
 
   // Rotates.
   EXPECT_EQ(one, one.rotl(0));
@@ -2024,6 +2024,24 @@ TEST(APIntTest, LogicalRightShift) {
   EXPECT_EQ(0, neg_one.lshr(128));
 }
 
+TEST(APIntTest, ArithmeticRightShift) {
+  // Ensure we handle large shifts of multi-word.
+  const APInt signmin32(APInt::getSignedMinValue(32));
+  EXPECT_TRUE(signmin32.ashr(32).isAllOnesValue());
+
+  // Ensure we handle large shifts of multi-word.
+  const APInt umax32(APInt::getSignedMaxValue(32));
+  EXPECT_EQ(0, umax32.ashr(32));
+
+  // Ensure we handle large shifts of multi-word.
+  const APInt signmin128(APInt::getSignedMinValue(128));
+  EXPECT_TRUE(signmin128.ashr(128).isAllOnesValue());
+
+  // Ensure we handle large shifts of multi-word.
+  const APInt umax128(APInt::getSignedMaxValue(128));
+  EXPECT_EQ(0, umax128.ashr(128));
+}
+
 TEST(APIntTest, LeftShift) {
   APInt i256(APInt::getLowBitsSet(256, 2));