Implement constant folding for bitreverse

llvm-svn: 263945

1 files changed, 30 insertions, 0 deletions

diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index 83455f67665..970c703cb51 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -787,6 +787,36 @@ APInt APInt::byteSwap() const {
   return Result;
 }
 
+APInt APInt::reverseBits() const {
+  switch (BitWidth) {
+  case 64:
+    return APInt(BitWidth, llvm::reverseBits<uint64_t>(VAL));
+  case 32:
+    return APInt(BitWidth, llvm::reverseBits<uint32_t>(VAL));
+  case 16:
+    return APInt(BitWidth, llvm::reverseBits<uint16_t>(VAL));
+  case 8:
+    return APInt(BitWidth, llvm::reverseBits<uint8_t>(VAL));
+  default:
+    break;
+  }
+
+  APInt Val(*this);
+  APInt Reversed(*this);
+  int S = BitWidth - 1;
+
+  const APInt One(BitWidth, 1);
+
+  for ((Val = Val.lshr(1)); Val != 0; (Val = Val.lshr(1))) {
+    Reversed <<= 1;
+    Reversed |= (Val & One);
+    --S;
+  }
+
+  Reversed <<= S;
+  return Reversed;
+}
+
 APInt llvm::APIntOps::GreatestCommonDivisor(const APInt& API1,
                                             const APInt& API2) {
   APInt A = API1, B = API2;