[ConstantRange] Handle `Intrinsic::cttz` (#67917)

This patch adds support for `Intrinsic::cttz` in ConstantRange. It
calculates the range in O(1) with the LCP-based method.

Migrated from https://reviews.llvm.org/D153505.

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/unittests/IR/ConstantRangeTest.cpp b/llvm/unittests/IR/ConstantRangeTest.cpp
index 12facfb..e505af5 100644
--- a/llvm/unittests/IR/ConstantRangeTest.cpp
+++ b/llvm/unittests/IR/ConstantRangeTest.cpp
@@ -2438,6 +2438,20 @@ TEST_F(ConstantRangeTest, Ctlz) {
       });
 }
 
+TEST_F(ConstantRangeTest, Cttz) {
+  TestUnaryOpExhaustive(
+      [](const ConstantRange &CR) { return CR.cttz(); },
+      [](const APInt &N) { return APInt(N.getBitWidth(), N.countr_zero()); });
+
+  TestUnaryOpExhaustive(
+      [](const ConstantRange &CR) { return CR.cttz(/*ZeroIsPoison=*/true); },
+      [](const APInt &N) -> std::optional<APInt> {
+        if (N.isZero())
+          return std::nullopt;
+        return APInt(N.getBitWidth(), N.countr_zero());
+      });
+}
+
 TEST_F(ConstantRangeTest, Ctpop) {
   TestUnaryOpExhaustive(
       [](const ConstantRange &CR) { return CR.ctpop(); },