Merge pull request #5519 from shajrawi/constant_propagation_int_ctlz

[SILOptimizer] Add ctlz support to constant propagation

Author: Joe Shajrawi

lib/SILOptimizer/Mandatory/ConstantPropagation.cpp

@@ -176,6 +176,33 @@ static SILInstruction *constantFoldIntrinsic(BuiltinInst *BI,
     return Op1;
   }
 
+  case llvm::Intrinsic::ctlz: {
+    assert(BI->getArguments().size() == 2 && "Ctlz should have 2 args.");
+    OperandValueArrayRef Args = BI->getArguments();
+
+    // Fold for integer constant arguments.
+    auto *LHS = dyn_cast<IntegerLiteralInst>(Args[0]);
+    if (!LHS) {
+      return nullptr;
+    }
+    APInt LHSI = LHS->getValue();
+    unsigned LZ = 0;
+    // Check corner-case of source == zero
+    if (LHSI.getLimitedValue() == 0) {
+      auto *RHS = dyn_cast<IntegerLiteralInst>(Args[1]);
+      if (!RHS || RHS->getValue().getBoolValue() != 0) {
+        // Undefined
+        return nullptr;
+      }
+      LZ = LHSI.getBitWidth();
+    } else {
+      LZ = LHSI.countLeadingZeros();
+    }
+    APInt LZAsAPInt = APInt(LHSI.getBitWidth(), LZ);
+    SILBuilderWithScope B(BI);
+    return B.createIntegerLiteral(BI->getLoc(), LHS->getType(), LZAsAPInt);
+  }
+
   case llvm::Intrinsic::sadd_with_overflow:
   case llvm::Intrinsic::uadd_with_overflow:
   case llvm::Intrinsic::ssub_with_overflow:

test/SILOptimizer/constant_propagation.sil

@@ -19,6 +19,36 @@ struct UInt64 {
   var value: Builtin.Int64
 }
 
+sil @count_leading_zeros_corner_case : $@convention(thin) () -> Builtin.Int64 {
+bb0:
+ %zero64 = integer_literal $Builtin.Int64, 0
+ %zero1 = integer_literal $Builtin.Int1, 0
+ %ctlz = builtin "int_ctlz_Int64"(%zero64 : $Builtin.Int64, %zero1 : $Builtin.Int1) : $Builtin.Int64
+ return %ctlz : $Builtin.Int64
+ 
+// CHECK-LABEL: sil @count_leading_zeros_corner_case
+// CHECK-NOT: integer_literal $Builtin.Int64, 0
+// CHECK-NOT: integer_literal $Builtin.Int1, 0
+// CHECK-NOT: builtin
+// CHECK: [[RES:%.*]] = integer_literal $Builtin.Int64, 64
+// CHECK-NEXT: return [[RES]] : $Builtin.Int64
+}
+
+sil @count_leading_zeros : $@convention(thin) () -> Builtin.Int64 {
+bb0:
+ %zero64 = integer_literal $Builtin.Int64, 2
+ %zero1 = integer_literal $Builtin.Int1, 0
+ %ctlz = builtin "int_ctlz_Int64"(%zero64 : $Builtin.Int64, %zero1 : $Builtin.Int1) : $Builtin.Int64
+ return %ctlz : $Builtin.Int64
+ 
+// CHECK-LABEL: sil @count_leading_zeros
+// CHECK-NOT: integer_literal $Builtin.Int64, 2
+// CHECK-NOT: integer_literal $Builtin.Int1, 0
+// CHECK-NOT: builtin
+// CHECK: [[RES:%.*]] = integer_literal $Builtin.Int64, 62
+// CHECK-NEXT: return [[RES]] : $Builtin.Int64
+}
+
 // Compute an expression using a chain of arithmetic with overflow instructions: 2 * (2 + 3) - 3
 sil @fold_arithmetic_with_overflow : $@convention(thin) () -> Builtin.Int64 {
 bb0: