From 11ecdf2ec699c5f78ef7b2bc1bd34618394cc9fa Mon Sep 17 00:00:00 2001
From: Damien George <damien.p.george@gmail.com>
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 a3a1cf341..95496b380 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 59b97d8ee..6195db63c 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 cd3dee364..895b2029e 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
--
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