Ryujit/ARM32 Implement Lowering::LowerCast for ARM

Simple integer to interger type conversion is passed.
Add comment for LowreCast with C++ comment style.

Signed-off-by: Hyung-Kyu Choi <hk0110.choi@samsung.com>

src/jit/lowerarm.cpp

@@ -32,10 +32,76 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 #include "lower.h"
 #include "lsra.h"
 
-/* Lowering of GT_CAST nodes */
+//------------------------------------------------------------------------
+// LowerCast: Lower GT_CAST(srcType, DstType) nodes.
+//
+// Arguments:
+// tree - GT_CAST node to be lowered
+//
+// Return Value:
+// None.
+//
+// Notes:
+// Casts from small int type to float/double are transformed as follows:
+// GT_CAST(byte, float/double) = GT_CAST(GT_CAST(byte, int32), float/double)
+// GT_CAST(sbyte, float/double) = GT_CAST(GT_CAST(sbyte, int32), float/double)
+// GT_CAST(int16, float/double) = GT_CAST(GT_CAST(int16, int32), float/double)
+// GT_CAST(uint16, float/double) = GT_CAST(GT_CAST(uint16, int32), float/double)
+//
+// Similarly casts from float/double to a smaller int type are transformed as follows:
+// GT_CAST(float/double, byte) = GT_CAST(GT_CAST(float/double, int32), byte)
+// GT_CAST(float/double, sbyte) = GT_CAST(GT_CAST(float/double, int32), sbyte)
+// GT_CAST(float/double, int16) = GT_CAST(GT_CAST(double/double, int32), int16)
+// GT_CAST(float/double, uint16) = GT_CAST(GT_CAST(double/double, int32), uint16)
+//
+// Note that for the overflow conversions we still depend on helper calls and
+// don't expect to see them here.
+// i) GT_CAST(float/double, int type with overflow detection)
+
 void Lowering::LowerCast(GenTree* tree)
 {
- NYI_ARM("ARM Lowering for cast");
+ assert(tree->OperGet() == GT_CAST);
+
+ JITDUMP("LowerCast for: ");
+ DISPNODE(tree);
+ JITDUMP("\n");
+
+ GenTreePtr op1 = tree->gtOp.gtOp1;
+ var_types dstType = tree->CastToType();
+ var_types srcType = op1->TypeGet();
+ var_types tmpType = TYP_UNDEF;
+
+ // TODO-ARM-Cleanup: Remove following NYI assertions.
+ if (varTypeIsFloating(srcType))
+ {
+ NYI_ARM("Lowering for cast from float"); // Not tested yet.
+ noway_assert(!tree->gtOverflow());
+ }
+
+ // Case of src is a small type and dst is a floating point type.
+ if (varTypeIsSmall(srcType) && varTypeIsFloating(dstType))
+ {
+ NYI_ARM("Lowering for cast from small type to float"); // Not tested yet.
+ // These conversions can never be overflow detecting ones.
+ noway_assert(!tree->gtOverflow());
+ tmpType = TYP_INT;
+ }
+ // case of src is a floating point type and dst is a small type.
+ else if (varTypeIsFloating(srcType) && varTypeIsSmall(dstType))
+ {
+ NYI_ARM("Lowering for cast from float to small type"); // Not tested yet.
+ tmpType = TYP_INT;
+ }
+
+ if (tmpType != TYP_UNDEF)
+ {
+ GenTreePtr tmp = comp->gtNewCastNode(tmpType, op1, tmpType);
+ tmp->gtFlags |= (tree->gtFlags & (GTF_UNSIGNED | GTF_OVERFLOW | GTF_EXCEPT));
+
+ tree->gtFlags &= ~GTF_UNSIGNED;
+ tree->gtOp.gtOp1 = tmp;
+ BlockRange().InsertAfter(op1, tmp);
+ }
 }
 
 void Lowering::LowerRotate(GenTreePtr tree)