[ConstantRange] Add toKnownBits() method

Add toKnownBits() method to mirror fromKnownBits(). We know the
top bits that are constant between min and max.

The return value for an empty range is chosen to be conservative.

1 files changed, 19 insertions, 0 deletions

diff --git a/llvm/unittests/IR/ConstantRangeTest.cpp b/llvm/unittests/IR/ConstantRangeTest.cpp
index 2c54b1c6..9aee84e 100644
--- a/llvm/unittests/IR/ConstantRangeTest.cpp
+++ b/llvm/unittests/IR/ConstantRangeTest.cpp
@@ -2366,6 +2366,25 @@ TEST_F(ConstantRangeTest, FromKnownBitsExhaustive) {
   }
 }
 
+TEST_F(ConstantRangeTest, ToKnownBits) {
+  unsigned Bits = 4;
+  EnumerateConstantRanges(Bits, [&](const ConstantRange &CR) {
+    KnownBits Known = CR.toKnownBits();
+    KnownBits ExpectedKnown(Bits);
+    ExpectedKnown.Zero.setAllBits();
+    ExpectedKnown.One.setAllBits();
+    ForeachNumInConstantRange(CR, [&](const APInt &N) {
+      ExpectedKnown.One &= N;
+      ExpectedKnown.Zero &= ~N;
+    });
+    // For an empty CR any result would be legal.
+    if (!CR.isEmptySet()) {
+      EXPECT_EQ(ExpectedKnown.One, Known.One);
+      EXPECT_EQ(ExpectedKnown.Zero, Known.Zero);
+    }
+  });
+}
+
 TEST_F(ConstantRangeTest, Negative) {
   // All elements in an empty set (of which there are none) are both negative
   // and non-negative. Empty & full sets checked explicitly for clarity, but