[llvm] bcb15d0 - [APInt] Slightly simplify APInt::ashrSlowCase. NFC (#111220)

[via llvm-commits]

Author: Craig Topper
Date: 2024-10-05T10:25:50-07:00
New Revision: bcb15d00596f8f25310887494f171e7f70386e7c

URL: https://github.com/llvm/llvm-project/commit/bcb15d00596f8f25310887494f171e7f70386e7c
DIFF: https://github.com/llvm/llvm-project/commit/bcb15d00596f8f25310887494f171e7f70386e7c.diff

LOG: [APInt] Slightly simplify APInt::ashrSlowCase. NFC (#111220)

Use an arithmetic shift for the last word copy when BitShift!=0. This
avoids an explicit sign extend after the shift.

Added: 
    

Modified: 
    llvm/lib/Support/APInt.cpp

Removed: 
    


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diff  --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index 2348a4c9b795e1..23e365f16d8fea 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -1055,11 +1055,10 @@ void APInt::ashrSlowCase(unsigned ShiftAmt) {
         U.pVal[i] = (U.pVal[i + WordShift] >> BitShift) |
                     (U.pVal[i + WordShift + 1] << (APINT_BITS_PER_WORD - BitShift));
 
-      // Handle the last word which has no high bits to copy.
-      U.pVal[WordsToMove - 1] = U.pVal[WordShift + WordsToMove - 1] >> BitShift;
-      // Sign extend one more time.
+      // Handle the last word which has no high bits to copy. Use an arithmetic
+      // shift to preserve the sign bit.
       U.pVal[WordsToMove - 1] =
-          SignExtend64(U.pVal[WordsToMove - 1], APINT_BITS_PER_WORD - BitShift);
+          (int64_t)U.pVal[WordShift + WordsToMove - 1] >> BitShift;
     }
   }