Avoid undefined behavior.

Author: ncruces

libc-top-half/musl/src/string/strlen.c

@@ -16,13 +16,16 @@ size_t strlen(const char *s)
 #if defined(__wasm_simd128__) && defined(__wasilibc_simd_string)
 	// strlen must stop as soon as it finds the terminator.
 	// Aligning ensures loads beyond the terminator are safe.
+	// Casting through uintptr_t makes this implementation-defined,
+	// rather than undefined behavior.
 	uintptr_t align = (uintptr_t)s % sizeof(v128_t);
-	const v128_t *v = (v128_t *)(s - align);
+	const v128_t *v = (v128_t *)((uintptr_t)s - align);
 
 	for (;;) {
+		const v128_t vv = *v;
 		// Bitmask is slow on AArch64, all_true is much faster.
-		if (!wasm_i8x16_all_true(*v)) {
-			const v128_t cmp = wasm_i8x16_eq(*v, (v128_t){});
+		if (!wasm_i8x16_all_true(vv)) {
+			const v128_t cmp = wasm_i8x16_eq(vv, (v128_t){});
 			// Clear the bits corresponding to alignment (little-endian)
 			// so we can count trailing zeros.
 			int mask = wasm_i8x16_bitmask(cmp) >> align << align;