[APInt] Add APInt::setBits() method to set all bits in range
The current pattern for setting bits in range is typically:
Mask |= APInt::getBitsSet(MaskSizeInBits, LoPos, HiPos);
Which can be particularly slow for large APInts (MaskSizeInBits > 64) as they require the allocation memory for the temporary variable.
This is one of the key compile time issues identified in PR32037.
This patch adds the APInt::setBits() helper method which avoids the temporary memory allocation completely, this first implementation uses setBit() internally instead but already significantly reduces the regression in PR32037 (~10% drop). Additional optimization may be possible.
I investigated whether there is need for APInt::clearBits() and APInt::flipBits() equivalents but haven't seen these patterns to be particularly common, but reusing the code would be trivial.
Differential Revision: https://reviews.llvm.org/D30265
llvm-svn: 296102
diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index 35c15e0..8ddbbe3 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -565,6 +565,39 @@
pVal[whichWord(bitPosition)] |= maskBit(bitPosition);
}
+void APInt::setBits(unsigned loBit, unsigned hiBit) {
+ assert(hiBit <= BitWidth && "hiBit out of range");
+ assert(loBit <= hiBit && loBit <= BitWidth && "loBit out of range");
+
+ if (loBit == hiBit)
+ return;
+
+ if (isSingleWord())
+ *this |= APInt::getBitsSet(BitWidth, loBit, hiBit);
+ else {
+ unsigned hiBit1 = hiBit - 1;
+ unsigned loWord = whichWord(loBit);
+ unsigned hiWord = whichWord(hiBit1);
+ if (loWord == hiWord) {
+ // Set bits are all within the same word, create a [loBit,hiBit) mask.
+ uint64_t mask = UINT64_MAX;
+ mask >>= (APINT_BITS_PER_WORD - (hiBit - loBit));
+ mask <<= whichBit(loBit);
+ pVal[loWord] |= mask;
+ } else {
+ // Set bits span multiple words, create a lo mask with set bits starting
+ // at loBit, a hi mask with set bits below hiBit and set all bits of the
+ // words in between.
+ uint64_t loMask = UINT64_MAX << whichBit(loBit);
+ uint64_t hiMask = UINT64_MAX >> (64 - whichBit(hiBit1) - 1);
+ pVal[loWord] |= loMask;
+ pVal[hiWord] |= hiMask;
+ for (unsigned word = loWord + 1; word < hiWord; ++word)
+ pVal[word] = UINT64_MAX;
+ }
+ }
+}
+
/// Set the given bit to 0 whose position is given as "bitPosition".
/// @brief Set a given bit to 0.
void APInt::clearBit(unsigned bitPosition) {