[APInt] Add a utility method to change the bit width and storage size of an APInt.

topperc · topperc · commit a92fd0bebb9e · 2017-05-12T01:46:01.000Z
Summary: This adds a resize method to APInt that manages deleting/allocating storage for an APInt and changes its bit width. Use this to simplify code in copy assignment and divide. The assignment code in particular was overly complicated. Treating every possible case as a separate implementation. I'm also pretty sure the clearUnusedBits code at the end was unnecessary. Since we always copying whole words from the source APInt. All unused bits should be clear in the source. Reviewers: hans, RKSimon Reviewed By: RKSimon Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D33073 llvm-svn: 302863
diff --git a/llvm/include/llvm/ADT/APInt.h b/llvm/include/llvm/ADT/APInt.h
@@ -157,6 +157,11 @@ class LLVM_NODISCARD APInt {
     return isSingleWord() ? U.VAL : U.pVal[whichWord(bitPosition)];
   }
 
+  /// Utility method to change the bit width of this APInt to new bit width,
+  /// allocating and/or deallocating as necessary. There is no guarantee on the
+  /// value of any bits upon return. Caller should populate the bits after.
+  void reallocate(unsigned NewBitWidth);
+
   /// \brief Convert a char array into an APInt
   ///
   /// \param radix 2, 8, 10, 16, or 36
diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
@@ -122,35 +122,38 @@ APInt::APInt(unsigned numbits, StringRef Str, uint8_t radix)
   fromString(numbits, Str, radix);
 }
 
+void APInt::reallocate(unsigned NewBitWidth) {
+  // If the number of words is the same we can just change the width and stop.
+  if (getNumWords() == getNumWords(NewBitWidth)) {
+    BitWidth = NewBitWidth;
+    return;
+  }
+
+  // If we have an allocation, delete it.
+  if (!isSingleWord())
+    delete [] U.pVal;
+
+  // Update BitWidth.
+  BitWidth = NewBitWidth;
+
+  // If we are supposed to have an allocation, create it.
+  if (!isSingleWord())
+    U.pVal = getMemory(getNumWords());
+}
+
 void APInt::AssignSlowCase(const APInt& RHS) {
   // Don't do anything for X = X
   if (this == &RHS)
     return;
 
-  if (BitWidth == RHS.getBitWidth()) {
-    // assume same bit-width single-word case is already handled
-    assert(!isSingleWord());
-    memcpy(U.pVal, RHS.U.pVal, getNumWords() * APINT_WORD_SIZE);
-    return;
-  }
+  // Adjust the bit width and handle allocations as necessary.
+  reallocate(RHS.getBitWidth());
 
-  if (isSingleWord()) {
-    // assume case where both are single words is already handled
-    assert(!RHS.isSingleWord());
-    U.pVal = getMemory(RHS.getNumWords());
-    memcpy(U.pVal, RHS.U.pVal, RHS.getNumWords() * APINT_WORD_SIZE);
-  } else if (getNumWords() == RHS.getNumWords())
-    memcpy(U.pVal, RHS.U.pVal, RHS.getNumWords() * APINT_WORD_SIZE);
-  else if (RHS.isSingleWord()) {
-    delete [] U.pVal;
+  // Copy the data.
+  if (isSingleWord())
     U.VAL = RHS.U.VAL;
-  } else {
-    delete [] U.pVal;
-    U.pVal = getMemory(RHS.getNumWords());
-    memcpy(U.pVal, RHS.U.pVal, RHS.getNumWords() * APINT_WORD_SIZE);
-  }
-  BitWidth = RHS.BitWidth;
-  clearUnusedBits();
+  else
+    memcpy(U.pVal, RHS.U.pVal, getNumWords() * APINT_WORD_SIZE);
 }
 
 /// This method 'profiles' an APInt for use with FoldingSet.
@@ -1500,16 +1503,9 @@ void APInt::divide(const APInt &LHS, unsigned lhsWords, const APInt &RHS,
   // If the caller wants the quotient
   if (Quotient) {
     // Set up the Quotient value's memory.
-    if (Quotient->BitWidth != LHS.BitWidth) {
-      if (Quotient->isSingleWord())
-        Quotient->U.VAL = 0;
-      else
-        delete [] Quotient->U.pVal;
-      Quotient->BitWidth = LHS.BitWidth;
-      if (!Quotient->isSingleWord())
-        Quotient->U.pVal = getClearedMemory(Quotient->getNumWords());
-    } else
-      Quotient->clearAllBits();
+    Quotient->reallocate(LHS.BitWidth);
+    // Clear out any previous bits.
+    Quotient->clearAllBits();
 
     // The quotient is in Q. Reconstitute the quotient into Quotient's low
     // order words.
@@ -1531,16 +1527,9 @@ void APInt::divide(const APInt &LHS, unsigned lhsWords, const APInt &RHS,
   // If the caller wants the remainder
   if (Remainder) {
     // Set up the Remainder value's memory.
-    if (Remainder->BitWidth != RHS.BitWidth) {
-      if (Remainder->isSingleWord())
-        Remainder->U.VAL = 0;
-      else
-        delete [] Remainder->U.pVal;
-      Remainder->BitWidth = RHS.BitWidth;
-      if (!Remainder->isSingleWord())
-        Remainder->U.pVal = getClearedMemory(Remainder->getNumWords());
-    } else
-      Remainder->clearAllBits();
+    Remainder->reallocate(RHS.BitWidth);
+    // Clear out any previous bits.
+    Remainder->clearAllBits();
 
     // The remainder is in R. Reconstitute the remainder into Remainder's low
     // order words.
