[Const Evaluator] Make compile-time constant evaluator correctly handle

s_to_s_checked_trunc_IntLiteral_IntNN where the bit width of the source
symbolic value (an APInt) could be smaller than the destination bits.

Author: ravikandhadai

lib/SILOptimizer/Utils/ConstExpr.cpp

@@ -448,30 +448,35 @@ ConstExprFunctionState::computeConstantValueBuiltin(BuiltinInst *inst) {
       if (operand.getKind() != SymbolicValue::Integer)
         return unknownResult();
 
-      auto operandVal = operand.getIntegerValue();
+      APInt operandVal = operand.getIntegerValue();
       uint32_t srcBitWidth = operandVal.getBitWidth();
       auto dstBitWidth =
           builtin.Types[1]->castTo<BuiltinIntegerType>()->getGreatestWidth();
 
-      APInt result = operandVal.trunc(dstBitWidth);
+      // Note that the if the source type is a Builtin.IntLiteral, operandVal
+      // could have fewer bits than the destination bit width and may only
+      // require a sign extension.
+      APInt result = operandVal.sextOrTrunc(dstBitWidth);
 
-      // Compute the overflow by re-extending the value back to its source and
-      // checking for loss of value.
-      APInt reextended =
-          dstSigned ? result.sext(srcBitWidth) : result.zext(srcBitWidth);
-      bool overflowed = (operandVal != reextended);
+      // Determine if there is a overflow.
+      if (operandVal.getBitWidth() > dstBitWidth) {
+        // Re-extend the value back to its source and check for loss of value.
+        APInt reextended =
+            dstSigned ? result.sext(srcBitWidth) : result.zext(srcBitWidth);
+        bool overflowed = (operandVal != reextended);
 
-      if (!srcSigned && dstSigned)
-        overflowed |= result.isSignBitSet();
+        if (!srcSigned && dstSigned)
+          overflowed |= result.isSignBitSet();
 
-      if (overflowed)
-        return evaluator.getUnknown(SILValue(inst), UnknownReason::Overflow);
+        if (overflowed)
+          return evaluator.getUnknown(SILValue(inst), UnknownReason::Overflow);
+      }
 
       auto &allocator = evaluator.getAllocator();
       // Build the Symbolic value result for our truncated value.
       return SymbolicValue::getAggregate(
           {SymbolicValue::getInteger(result, allocator),
-           SymbolicValue::getInteger(APInt(1, overflowed), allocator)},
+           SymbolicValue::getInteger(APInt(1, false), allocator)},
           allocator);
     };
 

test/SILOptimizer/constant_evaluator_test.sil

@@ -153,6 +153,15 @@ bb0:
   return %2 : $(Builtin.Int8)
 } // CHECK: Returns int: -1
 
+// CHECK-LABEL: @interpretSignedTruncWithIntLiteral
+sil @interpretSignedTruncWithIntLiteral : $@convention(thin) () -> Builtin.Int64 {
+bb0:
+  %0 = integer_literal $Builtin.IntLiteral, 5
+  %1 = builtin "s_to_s_checked_trunc_IntLiteral_Int64"(%0 : $Builtin.IntLiteral) : $(Builtin.Int64, Builtin.Int1)
+  %2 = tuple_extract %1 : $(Builtin.Int64, Builtin.Int1), 0
+  return %2 : $(Builtin.Int64)
+} // CHECK: Returns int: 5
+
 // CHECK-LABEL: @interpretSignedExtend
 sil @interpretSignedExtend : $@convention(thin) () -> Builtin.Int64 {
 bb0: