[ARM GlobalISel] Support G_CTLZ and G_CTLZ_ZERO_UNDEF

We can now select CLZ via the TableGen'erated code, so support G_CTLZ
and G_CTLZ_ZERO_UNDEF throughout the pipeline for types <= s32.

Legalizer:
If the CLZ instruction is available, use it for both G_CTLZ and
G_CTLZ_ZERO_UNDEF. Otherwise, use a libcall for G_CTLZ_ZERO_UNDEF and
lower G_CTLZ in terms of it.

In order to achieve this we need to add support to the LegalizerHelper
for the legalization of G_CTLZ_ZERO_UNDEF for s32 as a libcall (__clzsi2).

We also need to allow lowering of G_CTLZ in terms of G_CTLZ_ZERO_UNDEF
if that is supported as a libcall, as opposed to just if it is Legal or
Custom. Due to a minor refactoring of the helper function in charge of
this, we will also allow the same behaviour for G_CTTZ and G_CTPOP.
This is not going to be a problem in practice since we don't yet have
support for treating G_CTTZ and G_CTPOP as libcalls (not even in
DAGISel).

Reg bank select:
Map G_CTLZ to GPR. G_CTLZ_ZERO_UNDEF should not make it to this point.

Instruction select:
Nothing to do.

llvm-svn: 347545

1 files changed, 27 insertions, 0 deletions

diff --git a/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp b/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
index 0cc989be3c0..f0527611975 100644
--- a/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
+++ b/llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp
@@ -148,6 +148,33 @@ TEST_F(LegalizerHelperTest, LowerBitCountingCTLZ0) {
   ASSERT_TRUE(CheckMachineFunction(*MF, CheckStr));
 }
 
+// CTLZ expansion in terms of CTLZ_ZERO_UNDEF if the latter is a libcall
+TEST_F(LegalizerHelperTest, LowerBitCountingCTLZLibcall) {
+  if (!TM)
+    return;
+
+  // Declare your legalization info
+  DefineLegalizerInfo(
+      A, { getActionDefinitionsBuilder(G_CTLZ_ZERO_UNDEF).libcallFor({s64}); });
+  // Build
+  auto MIBCTLZ = B.buildInstr(TargetOpcode::G_CTLZ, LLT::scalar(64), Copies[0]);
+  AInfo Info(MF->getSubtarget());
+  LegalizerHelper Helper(*MF, Info);
+  ASSERT_TRUE(Helper.lower(*MIBCTLZ, 0, LLT::scalar(64)) ==
+              LegalizerHelper::LegalizeResult::Legalized);
+
+  auto CheckStr = R"(
+  CHECK: [[CZU:%[0-9]+]]:_(s64) = G_CTLZ_ZERO_UNDEF %0
+  CHECK: [[ZERO:%[0-9]+]]:_(s64) = G_CONSTANT i64 0
+  CHECK: [[THIRTY2:%[0-9]+]]:_(s64) = G_CONSTANT i64 64
+  CHECK: [[CMP:%[0-9]+]]:_(s1) = G_ICMP intpred(eq), %0:_(s64), [[ZERO]]
+  CHECK: [[SEL:%[0-9]+]]:_(s64) = G_SELECT [[CMP]]:_(s1), [[THIRTY2]]:_, [[CZU]]
+  )";
+
+  // Check
+  ASSERT_TRUE(CheckMachineFunction(*MF, CheckStr));
+}
+
 // CTLZ expansion
 TEST_F(LegalizerHelperTest, LowerBitCountingCTLZ1) {
   if (!TM)