[ADT] Add APInt::isNegatedPowerOf2() helper

Inspired by D111968, provide a isNegatedPowerOf2() wrapper instead of obfuscating code with (-Value).isPowerOf2() patterns, which I'm sure are likely avenues for typos.....

Differential Revision: https://reviews.llvm.org/D111998

1 files changed, 26 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
index 0efe28f..8a731633 100644
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -1785,6 +1785,32 @@ TEST(APIntTest, isPowerOf2) {
   }
 }
 
+TEST(APIntTest, isNegatedPowerOf2) {
+  EXPECT_FALSE(APInt(5, 0x00).isNegatedPowerOf2());
+  EXPECT_TRUE(APInt(15, 0x7ffe).isNegatedPowerOf2());
+  EXPECT_TRUE(APInt(16, 0xfffc).isNegatedPowerOf2());
+  EXPECT_TRUE(APInt(32, 0xffffffff).isNegatedPowerOf2());
+
+  for (int N : {1, 2, 3, 4, 7, 8, 16, 32, 64, 127, 128, 129, 256}) {
+    EXPECT_FALSE(APInt(N, 0).isNegatedPowerOf2());
+    EXPECT_TRUE(APInt::getAllOnes(N).isNegatedPowerOf2());
+    EXPECT_TRUE(APInt::getSignedMinValue(N).isNegatedPowerOf2());
+    EXPECT_TRUE((-APInt::getSignedMinValue(N)).isNegatedPowerOf2());
+
+    APInt One(N, 1);
+    for (int I = 1; I < N - 1; ++I) {
+      EXPECT_FALSE(APInt::getOneBitSet(N, I).isNegatedPowerOf2());
+      EXPECT_TRUE((-APInt::getOneBitSet(N, I)).isNegatedPowerOf2());
+
+      APInt MaskVal = One.shl(I);
+      EXPECT_TRUE((-MaskVal).isNegatedPowerOf2());
+
+      APInt ShiftMaskVal = One.getHighBitsSet(N, I);
+      EXPECT_TRUE(ShiftMaskVal.isNegatedPowerOf2());
+    }
+  }
+}
+
 // Test that self-move works with EXPENSIVE_CHECKS. It calls std::shuffle which
 // does self-move on some platforms.
 #ifdef EXPENSIVE_CHECKS