Correct type conversion for default arguments.

The code didn't take into account of the possible truncation of the
argument, we don't want to convert the default value to the type of the
register but rather to the type of the destination one.

Author: LemonBoy

src/vm/moar/QAST/QASTCompilerMAST.nqp

@@ -1163,41 +1163,50 @@ my class MASTCompilerInstance {
                             ?? $block.lexical_param($var.name)
                             !! $block.local($var.name);
                         my $valreg;
+                        my $valreg_kind;
                         my $truncop;
+
                         if $param_kind == $MVM_reg_obj || $param_kind == $MVM_reg_int64 ||
                                 $param_kind == $MVM_reg_num64 || $param_kind == $MVM_reg_str ||
                                 $param_kind == $MVM_reg_uint64 {
+                            $valreg_kind := $param_kind;
                             $valreg := $targetreg;
                         }
                         elsif $param_kind == $MVM_reg_num32 {
-                            $valreg := $*REGALLOC.fresh_register($MVM_reg_num64);
+                            $valreg_kind := $MVM_reg_num64;
                             $truncop := 'trunc_n32';
                         }
                         elsif $param_kind == $MVM_reg_int32 {
-                            $valreg := $*REGALLOC.fresh_register($MVM_reg_int64);
+                            $valreg_kind := $MVM_reg_int64;
                             $truncop := 'trunc_i32';
                         }
                         elsif $param_kind == $MVM_reg_int16 {
-                            $valreg := $*REGALLOC.fresh_register($MVM_reg_int64);
+                            $valreg_kind := $MVM_reg_int64;
                             $truncop := 'trunc_i16';
                         }
                         elsif $param_kind == $MVM_reg_int8 {
-                            $valreg := $*REGALLOC.fresh_register($MVM_reg_int64);
+                            $valreg_kind := $MVM_reg_int64;
                             $truncop := 'trunc_i8';
                         }
                         elsif $param_kind == $MVM_reg_uint32 {
-                            $valreg := $*REGALLOC.fresh_register($MVM_reg_uint64);
+                            $valreg_kind := $MVM_reg_uint64;
                             $truncop := 'trunc_u32';
                         }
                         elsif $param_kind == $MVM_reg_uint16 {
-                            $valreg := $*REGALLOC.fresh_register($MVM_reg_uint64);
+                            $valreg_kind := $MVM_reg_uint64;
                             $truncop := 'trunc_u16';
                         }
                         elsif $param_kind == $MVM_reg_uint8 {
-                            $valreg := $*REGALLOC.fresh_register($MVM_reg_uint64);
+                            $valreg_kind := $MVM_reg_uint64;
                             $truncop := 'trunc_u8';
                         }
 
+                        # Get a fresh register to store the result of the
+                        # truncation, but only if needed
+                        if $valreg_kind != $param_kind {
+                            $valreg := $*REGALLOC.fresh_register($valreg_kind);
+                        }
+
                         # NQP->QAST always provides a default value for optional NQP params
                         # even if no default initializer expression is provided.
                         if $var.default {
@@ -1206,7 +1215,7 @@ my class MASTCompilerInstance {
 
                             # generate default initialization code. Could also be
                             # wrapped in another QAST::Block.
-                            my $default_mast := self.as_mast($var.default, :want($param_kind));
+                            my $default_mast := self.as_mast($var.default, :want($valreg_kind));
 
                             # emit param grabbing op
                             $val2