From 1cf0ce094a4a1571b7404643e7a3b992592317a5 Mon Sep 17 00:00:00 2001 From: Damien George Date: Mon, 19 Aug 2019 15:51:40 +1000 Subject: [PATCH] py/nlr: Use MP_UNREACHABLE at the end of arch-specific nlr_jump funcs. Recent versions of gcc perform optimisations which can lead to the following code from the MP_NLR_JUMP_HEAD macro being omitted: top->ret_val = val; \ MP_NLR_RESTORE_PYSTACK(top); \ *_top_ptr = top->prev; \ This is noticeable (at least) in the unix coverage on x86-64 built with gcc 9.1.0. This is because the nlr_jump function is marked as no-return, so gcc deduces that the above code has no effect. Adding MP_UNREACHABLE tells the compiler that the asm code may branch elsewhere, and so it cannot optimise away the code. --- py/nlrx64.c | 2 +- py/nlrx86.c | 2 +- py/nlrxtensa.c | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/py/nlrx64.c b/py/nlrx64.c index 9b2b22c225..569ad84fb0 100644 --- a/py/nlrx64.c +++ b/py/nlrx64.c @@ -108,7 +108,7 @@ NORETURN void nlr_jump(void *val) { : // clobbered registers ); - for (;;); // needed to silence compiler warning + MP_UNREACHABLE } #endif // MICROPY_NLR_X64 diff --git a/py/nlrx86.c b/py/nlrx86.c index 4900a4c0d2..6fbbe44327 100644 --- a/py/nlrx86.c +++ b/py/nlrx86.c @@ -100,7 +100,7 @@ NORETURN void nlr_jump(void *val) { : // clobbered registers ); - for (;;); // needed to silence compiler warning + MP_UNREACHABLE } #endif // MICROPY_NLR_X86 diff --git a/py/nlrxtensa.c b/py/nlrxtensa.c index d66c7a9a7f..5640350043 100644 --- a/py/nlrxtensa.c +++ b/py/nlrxtensa.c @@ -77,7 +77,7 @@ NORETURN void nlr_jump(void *val) { : // clobbered registers ); - for (;;); // needed to silence compiler warning + MP_UNREACHABLE } #endif // MICROPY_NLR_XTENSA