llvm bug?

alloca.c

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char const* argv[])
{
    while(1) {
        void *a = alloca(1024);
        fprintf(stderr, "%p\n", a);
    }
    return 0;
}

alloca.ll

; ModuleID = 'alloca.cpp'
%struct.x = type { i32 }

define void @f(%struct.x* nocapture %x) nounwind uwtable noinline ssp {
  ret void
}

define i32 @main(i32 %argc, i8** nocapture %argv) nounwind uwtable ssp {
  br label %1

; <label>:1                                       ; preds = %1, %0
  %i.01 = phi i32 [ 0, %0 ], [ %2, %1 ]
  %x = alloca %struct.x, align 4
  call void @f(%struct.x* %x)
  %2 = add nsw i32 %i.01, 1
  %exitcond = icmp eq i32 %2, 6000000
  br i1 %exitcond, label %3, label %1

; <label>:3                                       ; preds = %1
  ret i32 0
}

alloca_ok.ll

; ModuleID = 'alloca.cpp'

%struct.x = type { i32 }

define void @f(%struct.x* nocapture %x) nounwind uwtable noinline ssp {
entry:
  ret void
}

define i32 @main(i32 %argc, i8** nocapture %argv) nounwind uwtable ssp {
entry:
  %x = alloca %struct.x, align 4
  br label %for.body

for.body:                                         ; preds = %for.body, %entry
  %i.01 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
  call void @f(%struct.x* %x)
  %inc = add nsw i32 %i.01, 1
  %exitcond = icmp eq i32 %inc, 600000
  br i1 %exitcond, label %for.end, label %for.body

for.end:                                          ; preds = %for.body
  ret i32 0
}

result.txt

$ gdb -arg lli alloca.ll 
(gdb) r
Starting program: /usr/local/bin/lli alloca.ll
Reading symbols for shared libraries ++........................ done

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_PROTECTION_FAILURE at address: 0x00007fff5f3ffff8
0x000000010232502e in ?? ()
(gdb) bt
#0  0x000000010232502e in ?? ()
#1  0x000000010000ecb4 in llvm::JIT::runFunction (this=0x102402fd0, F=0x102401c00, ArgValues=@0x7fff5fbff0a0) at /Users/masa/src/llvm/lib/ExecutionEngine/JIT/JIT.cpp:428
#2  0x00000001001a0954 in llvm::ExecutionEngine::runFunctionAsMain (this=0x102402fd0, Fn=0x102401c00, argv=@0x100d37318, envp=0x7fff5fbff4b8) at /Users/masa/src/llvm/lib/ExecutionEngine/ExecutionEngine.cpp:398
#3  0x00000001000029c5 in main (argc=2, argv=0x7fff5fbff4a0, envp=0x7fff5fbff4b8) at /Users/masa/src/llvm/tools/lli/lli.cpp:286
(gdb)