Pass FP values to printf

On variadic function, it seems FP values are passed on GP registers.

RISC-V instruction: `fmv.x.d`

src/cc/arch/riscv64/ir_riscv64.c

@@ -664,6 +664,16 @@ static void ei_precall(IR *ir) {
 static void ei_pusharg(IR *ir) {
   assert(!(ir->opr1->flag & VRF_CONST));
   if (ir->opr1->flag & VRF_FLONUM) {
+#if VAARG_FP_AS_GP
+    if (ir->pusharg.fp_as_gp) {
+      switch (ir->opr1->vsize) {
+      case SZ_FLOAT:  FMV_X_W(kReg64s[ir->pusharg.index], kFReg32s[ir->opr1->phys]); break;
+      case SZ_DOUBLE:  FMV_X_D(kReg64s[ir->pusharg.index], kFReg64s[ir->opr1->phys]); break;
+      default: assert(false); break;
+      }
+      return;
+    }
+#endif
     // Assume parameter registers are arranged from index 0.
     if (ir->pusharg.index != ir->opr1->phys) {
       switch (ir->opr1->vsize) {

src/cc/arch/riscv64/riscv64.h

@@ -212,6 +212,9 @@
 #define FCVT_D_S(o1, o2)      EMIT_ASM("fcvt.d.s", o1, o2)   // double <- float
 #define FCVT_S_D(o1, o2)      EMIT_ASM("fcvt.s.d", o1, o2)   // float <- double
 
+#define FMV_X_W(o1, o2)      EMIT_ASM("fmv.x.w", o1, o2)  // int <- float(hex)
+#define FMV_X_D(o1, o2)      EMIT_ASM("fmv.x.d", o1, o2)  // int <- double(hex)
+
 #define FEQ_D(o1, o2, o3)     EMIT_ASM("feq.d", o1, o2, o3)
 #define FEQ_S(o1, o2, o3)     EMIT_ASM("feq.s", o1, o2, o3)
 #define FLT_D(o1, o2, o3)     EMIT_ASM("flt.d", o1, o2, o3)

src/cc/backend/codegen_expr.c

@@ -447,6 +447,9 @@ static VReg *gen_funcall(Expr *expr) {
     int size;
     bool stack_arg;
     bool is_flo;
+#if VAARG_FP_AS_GP
+    bool fp_as_gp;
+#endif
   } ArgInfo;
 
   ArgInfo *arg_infos = NULL;
@@ -468,6 +471,13 @@ static VReg *gen_funcall(Expr *expr) {
       assert(arg->type->kind != TY_ARRAY);
       p->size = type_size(arg->type);
       p->is_flo = is_flonum(arg->type);
+#if VAARG_FP_AS_GP
+      p->fp_as_gp = false;
+      if (functype->func.vaargs && functype->func.params != NULL && i >= functype->func.params->len) {
+        p->is_flo = false;
+        p->fp_as_gp = true;
+      }
+#endif
       p->stack_arg = is_stack_param(arg->type);
 #if VAARG_ON_STACK
       if (functype->func.vaargs && functype->func.params != NULL && i >= functype->func.params->len)
@@ -517,7 +527,13 @@ static VReg *gen_funcall(Expr *expr) {
           ++iregarg;
           int index = reg_arg_count - iregarg + arg_start;
           assert(index < MAX_REG_ARGS);
-          new_ir_pusharg(vreg, index);
+          IR *ir = new_ir_pusharg(vreg, index);
+#if !VAARG_FP_AS_GP
+          UNUSED(ir);
+#else
+          if (p->fp_as_gp)
+            ir->pusharg.fp_as_gp = true;
+#endif
         }
       } else {
         enum VRegSize offset_type = 2;  //{.size = 4, .align = 4};  // TODO:

src/cc/backend/ir.c

@@ -252,11 +252,15 @@ void new_ir_tjmp(VReg *val, BB **bbs, size_t len) {
   ir->tjmp.len = len;
 }
 
-void new_ir_pusharg(VReg *vreg, int index) {
+IR *new_ir_pusharg(VReg *vreg, int index) {
   assert(index >= 0);
   IR *ir = new_ir(IR_PUSHARG);
   ir->opr1 = vreg;
   ir->pusharg.index = index;
+#if VAARG_FP_AS_GP
+  ir->pusharg.fp_as_gp = false;
+#endif
+  return ir;
 }
 
 IR *new_ir_precall(int arg_count, int stack_args_size) {

src/cc/backend/ir.h

@@ -152,6 +152,9 @@ typedef struct IR {
     } precall;
     struct {
       int index;
+#if VAARG_FP_AS_GP
+      bool fp_as_gp;
+#endif
     } pusharg;
     struct {
       const Name *label;
@@ -183,7 +186,7 @@ void new_ir_jmp(BB *bb);  // Non-conditional jump
 void new_ir_cjmp(VReg *opr1, VReg *opr2, enum ConditionKind cond, BB *bb);  // Conditional jump
 void new_ir_tjmp(VReg *val, BB **bbs, size_t len);
 IR *new_ir_precall(int arg_count, int stack_args_size);
-void new_ir_pusharg(VReg *vreg, int index);
+IR *new_ir_pusharg(VReg *vreg, int index);
 VReg *new_ir_call(const Name *label, bool global, VReg *freg, int total_arg_count,
                   int reg_arg_count, enum VRegSize result_size, int result_flag, IR *precall,
                   VReg **args, int vaarg_start);

src/config.h

@@ -61,6 +61,11 @@
 #define VAARG_ON_STACK  1
 #endif
 
+#if !defined(VAARG_FP_AS_GP) && XCC_TARGET_ARCH == XCC_ARCH_RISCV64
+// Pass floating-point arguments in general-purpose registers for variadic arguments.
+#define VAARG_FP_AS_GP  1
+#endif
+
 #if !defined(MANGLE_PREFIX) && XCC_TARGET_PLATFORM == XCC_PLATFORM_APPLE
 #define MANGLE_PREFIX  "_"
 #endif