py/emitnative: Ensure stack settling is safe mid-branch.

And add a test for the case where REG_RET could be in use.

Fixes #7523.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

py/emitnative.c

@@ -877,7 +877,7 @@ STATIC vtype_kind_t load_reg_stack_imm(emit_t *emit, int reg_dest, const stack_i
 // Copies all unsettled registers and immediates that are Python values into the
 // concrete Python stack.  This ensures the concrete Python stack holds valid
 // values for the current stack_size.
-// This function may clobber REG_TEMP0.
+// This function may clobber REG_TEMP1.
 STATIC void need_stack_settled(emit_t *emit) {
     DEBUG_printf("  need_stack_settled; stack_size=%d\n", emit->stack_size);
     need_reg_all(emit);
@@ -886,8 +886,9 @@ STATIC void need_stack_settled(emit_t *emit) {
         if (si->kind == STACK_IMM) {
             DEBUG_printf("    imm(" INT_FMT ") to local(%u)\n", si->data.u_imm, emit->stack_start + i);
             si->kind = STACK_VALUE;
-            si->vtype = load_reg_stack_imm(emit, REG_TEMP0, si, false);
+            // using REG_TEMP1 to avoid clobbering REG_TEMP0 (aka REG_RET)
-            emit_native_mov_state_reg(emit, emit->stack_start + i, REG_TEMP0);
+            si->vtype = load_reg_stack_imm(emit, REG_TEMP1, si, false);
+            emit_native_mov_state_reg(emit, emit->stack_start + i, REG_TEMP1);
         }
     }
 }

tests/micropython/native_misc.py

@@ -38,3 +38,13 @@ def f(a):
 
 f(False)
 f(True)
+
+
+# stack settling in branch
+@micropython.native
+def f(a):
+    print(1, 2, 3, 4 if a else 5)
+
+
+f(False)
+f(True)

tests/micropython/native_misc.py.exp

@@ -4,3 +4,5 @@
 6
 True
 False
+1 2 3 5
+1 2 3 4