[PATCH] D111241: [APInt] Fix isAllOnes and extractBits for zero width values.

[Chris Lattner via Phabricator via llvm-commits]

lattner created this revision.
Herald added subscribers: dexonsmith, hiraditya.
lattner requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

isAllOnes() should return true for zero bit values because
there are no zeros in it.

Thanks to Jay Foad for pointing this out.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D111241

Files:
  llvm/include/llvm/ADT/APInt.h
  llvm/lib/Support/APInt.cpp
  llvm/unittests/ADT/APIntTest.cpp


Index: llvm/unittests/ADT/APIntTest.cpp
===================================================================
--- llvm/unittests/ADT/APIntTest.cpp
+++ llvm/unittests/ADT/APIntTest.cpp
@@ -2948,6 +2948,7 @@
   // Methods like getLowBitsSet work with zero bits.
   EXPECT_EQ(0U, APInt::getLowBitsSet(0, 0).getBitWidth());
   EXPECT_EQ(0U, APInt::getSplat(0, ZW).getBitWidth());
+  EXPECT_EQ(0U, APInt(4, 10).extractBits(0, 2).getBitWidth());
 
   // Logical operators.
   ZW |= ZW2;
@@ -2990,6 +2991,7 @@
   EXPECT_EQ(0U, ZW.getLoBits(0).getBitWidth());
   EXPECT_EQ(0, ZW.zext(4));
   EXPECT_EQ(0U, APInt(4, 3).trunc(0).getBitWidth());
+  EXPECT_EQ(1U, ZW.isAllOnes());
 
   SmallString<42> STR;
   ZW.toStringUnsigned(STR);
Index: llvm/lib/Support/APInt.cpp
===================================================================
--- llvm/lib/Support/APInt.cpp
+++ llvm/lib/Support/APInt.cpp
@@ -444,7 +444,6 @@
 }
 
 APInt APInt::extractBits(unsigned numBits, unsigned bitPosition) const {
-  assert(numBits > 0 && "Can't extract zero bits");
   assert(bitPosition < BitWidth && (numBits + bitPosition) <= BitWidth &&
          "Illegal bit extraction");
 
Index: llvm/include/llvm/ADT/APInt.h
===================================================================
--- llvm/include/llvm/ADT/APInt.h
+++ llvm/include/llvm/ADT/APInt.h
@@ -343,14 +343,12 @@
   /// \returns true if this APInt is non-positive.
   bool isNonPositive() const { return !isStrictlyPositive(); }
 
-  /// Determine if all bits are set.
+  /// Determine if all bits are set.  This is true for zero-width values.
   bool isAllOnes() const {
-    if (isSingleWord()) {
-      // Calculate the shift amount, handling the zero-bit wide case without UB.
-      unsigned ShiftAmt =
-          (APINT_BITS_PER_WORD - BitWidth) % APINT_BITS_PER_WORD;
-      return U.VAL == WORDTYPE_MAX >> ShiftAmt;
-    }
+    if (BitWidth == 0)
+      return true;
+    if (isSingleWord())
+      return U.VAL == WORDTYPE_MAX >> (APINT_BITS_PER_WORD - BitWidth);
     return countTrailingOnesSlowCase() == BitWidth;
   }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D111241.377580.patch
Type: text/x-patch
Size: 2067 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20211006/55af38c5/attachment.bin>