[LLVMbugs] [Bug 11468] Clang incorrectly handles exceptions in presence of stack aligned variables

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=11468

Alexey Samsonov <samsonov at google.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |

--- Comment #4 from Alexey Samsonov <samsonov at google.com> 2011-12-02 15:14:08 CST ---
Ouch, sorry for that. I tried to make another reproducer, please take a look:
$ cat exception_test.cc
#include <stdio.h>

__attribute__((noinline))
void TouchR15AndThrow(const char& arg) {
  volatile int n __attribute__((aligned(32))) = 0;
  asm volatile ("nop" : : : "%r15"); // force to save r15 on stack
  throw arg;
}

int main() {
  // Set r15 value
  int a = 42;
  asm ("movq %0, %%r15;\n\t" : : "g"(a) : "%r15");
  // Output value of r15
  int b;
  asm ("movq %%r15, %0;\n\t" : "=g" (b) : : "%r15");
  fprintf(stderr, "before = %d\n", b);
  try {
    TouchR15AndThrow('c');
  } catch (const char&) { }
  // Output value of r15 again
  asm ("movq %%r15, %0;\n\t" : "=g" (b) : : "%r15");
  fprintf(stderr, "after = %d\n", b);
  return 0;
}

$ ../build/Release+Asserts/bin/clang++ -O2 exception_test.cc
$ ./a.out
before = 42
after = 0

there is no instruction that changes value in %r15, but it is incorrectly
restored after exception is caught.

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