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Bug 27117 - LLVM generates unreachable call stack adjustments after noreturn functions when the frame is not reserved
Summary: LLVM generates unreachable call stack adjustments after noreturn functions wh...
Status: RESOLVED FIXED
Alias: None
Product: libraries
Classification: Unclassified
Component: Common Code Generator Code (show other bugs)
Version: trunk
Hardware: PC Windows NT
: P normal
Assignee: Unassigned LLVM Bugs
URL:
Keywords:
Depends on:
Blocks: 26299
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Reported: 2016-03-29 13:26 PDT by Reid Kleckner
Modified: 2016-05-20 10:52 PDT (History)
3 users (show)

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Description Reid Kleckner 2016-03-29 13:26:35 PDT 
Consider:

__declspec(noreturn) void crash(void *);
void g(void*);
void f(int c) {
  void *p = _alloca(c);
  if (c)
    crash(p);
  g(p);
}

Here is the call to 'crash':
.LBB0_1:                                # %if.then
        callq   "?crash@@YAXPEAX@Z"
        addq    $32, %rsp
        ud2

The ADD RSP instruction is dead. On Windows, it is very common to not have a reserved call frame because of inalloca.

Maybe the right fix here is to teach MI more about noreturn functions so we can do more general DCE after them. It would also help us get rid of TrapOnUnreachable in favor of inserting int3 after all noreturn calls.
Comment 1 Reid Kleckner 2016-03-29 13:27:53 PDT 
This is worth doing because it comes up on every assert-like construct.
Comment 2 Hans Wennborg 2016-05-20 10:52:54 PDT 
r270109