py/asmthumb: Fix T3 encoding of conditional branches.

agatti · dpgeorge · commit bd413d3d853e · 2025-08-19T12:40:29.000+10:00
This commit fixes the encoding of conditional branch opcodes emitted for ARMv7-M targets, when the emitter decides to use the T3 encoding for said operation. Fields J1 and J2 are now present in the generated opcode word, along with correcting some minor issues in bitmasks and shifts computation. This fixes #17940. Signed-off-by: Alessandro Gatti <a.gatti@frob.it>
diff --git a/py/asmthumb.c b/py/asmthumb.c
@@ -267,9 +267,8 @@ bool asm_thumb_b_n_label(asm_thumb_t *as, uint label) {
 
 #define OP_BCC_N(cond, byte_offset) (0xd000 | ((cond) << 8) | (((byte_offset) >> 1) & 0x00ff))
 
-// all these bit-arithmetic operations need coverage testing!
-#define OP_BCC_W_HI(cond, byte_offset) (0xf000 | ((cond) << 6) | (((byte_offset) >> 10) & 0x0400) | (((byte_offset) >> 14) & 0x003f))
-#define OP_BCC_W_LO(byte_offset) (0x8000 | ((byte_offset) & 0x2000) | (((byte_offset) >> 1) & 0x0fff))
+#define OP_BCC_W_HI(cond, byte_offset) (0xf000 | ((cond) << 6) | (((byte_offset) >> 10) & 0x0400) | (((byte_offset) >> 12) & 0x003f))
+#define OP_BCC_W_LO(byte_offset) (0x8000 | (((byte_offset) >> 5) & 0x2000) | (((byte_offset) >> 8) & 0x0800) | (((byte_offset) >> 1) & 0x07ff))
 
 bool asm_thumb_bcc_nw_label(asm_thumb_t *as, int cond, uint label, bool wide) {
     mp_uint_t dest = get_label_dest(as, label);
diff --git a/tests/micropython/viper_large_jump.py b/tests/micropython/viper_large_jump.py
@@ -0,0 +1,20 @@
+COUNT = 600
+
+
+try:
+    code = """
+@micropython.viper
+def f() -> int:
+    x = 0
+    while x < 10:
+"""
+    for i in range(COUNT):
+        code += "        x += 1\n"
+    code += "    return x"
+    exec(code)
+except MemoryError:
+    print("SKIP-TOO-LARGE")
+    raise SystemExit
+
+
+print(f())
diff --git a/tests/micropython/viper_large_jump.py.exp b/tests/micropython/viper_large_jump.py.exp
@@ -0,0 +1 @@
+600
