[llvm-bugs] [Bug 26009] New: wrong code (that hangs) at -Os and above on x86_64-linux-gnu in 32-bit mode

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=26009

            Bug ID: 26009
           Summary: wrong code (that hangs) at -Os and above on
                    x86_64-linux-gnu in 32-bit mode
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: su at cs.ucdavis.edu
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

The following code is miscompiled by the current clang trunk on
x86_64-linux-gnu at -Os and above in 32-bit mode (but not in 64-bit mode). 

This is a regression from 3.7.x.


$ clang-trunk -v
clang version 3.8.0 (trunk 256693)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/tools/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.2.1
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.2.1
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$ 
$ clang-trunk -m32 -O1 small.c; ./a.out
$ clang-trunk -m64 -Os small.c; ./a.out
$ clang-3.7.0 -m32 -Os small.c; ./a.out
$ 
$ clang-trunk -m32 -Os small.c
$ timeout -s 9 10 ./a.out
Killed
$ clang-trunk -m32 -O2 small.c
$ timeout -s 9 10 ./a.out
Killed
$ clang-trunk -m32 -O3 small.c
$ timeout -s 9 10 ./a.out
Killed
$ 


-----------------------------------------


unsigned char a, d, g;
static unsigned char *b = &a, *e = &d;
short c;
int f;

void
fn1 (int p1)
{
  short *h = &c;
  ++*h;
  *e = --*b >> 6 | (g != 0);
  if (a < 240 && c)
    for (;;)
      ;
}

int
main ()
{
  fn1 (f);
  return 0;
}

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