WRONG code. FE:@llvm.lifetime.end? DeadStoreElim?

[JonPsson1]

This program:

int printf(const char *, ...);

long RES;
unsigned ****c;
unsigned *****volatile P5 = &c;
static unsigned ****P4;

unsigned **P2a, **P2b;

int main() {
  {
    unsigned ***P3 = &P2a;
    for (unsigned IV = -8; IV; IV = IV + 4) {
      unsigned ***i = &P2b;
      long *P = &RES;
      *P5 = &i;
      *P = ( (P4 = &P3) == *P5 );
    }
  }
  printf("%d\n", RES);
}

should print '0', which it does, except if compiled with -Os on SystemZ:

clang -march=z15 -Os wrong0.i -o a.out -w; ./a.out
1

If I remove the extra curly braces around the loop, 0 is printed also with -Os. I see from the front-end only one slight difference with the braces in a block:

for.end:                                          ; pred        for.end:                                          ; pred
                                                           >      call void @llvm.lifetime.end.p0(i64 8, ptr %P3) #3
  %6 = load i64, ptr @RES, align 8, !tbaa !10                     %6 = load i64, ptr @RES, align 8, !tbaa !10
  %call = call signext i32 (ptr, ...) @printf(ptr nounde          %call = call signext i32 (ptr, ...) @printf(ptr nounde
  call void @llvm.lifetime.end.p0(i64 8, ptr %P3) #3       <
  %7 = load i32, ptr %retval, align 4                             %7 = load i32, ptr %retval, align 4
  ret i32 %7                                                      ret i32 %7
}

Many passes later, the next change then is after DSE where a store now has been removed:

; *** IR Dump After DSEPass on main ***                         ; *** IR Dump After DSEPass on main ***
; Function Attrs: nounwind optsize                              ; Function Attrs: nounwind optsize
define dso_local signext i32 @main() local_unnamed_addr         define dso_local signext i32 @main() local_unnamed_addr 
entry:                                                          entry:
  %P3 = alloca ptr, align 8                                       %P3 = alloca ptr, align 8
  %i = alloca ptr, align 8                                        %i = alloca ptr, align 8
  call void @llvm.lifetime.start.p0(i64 8, ptr nonnull %          call void @llvm.lifetime.start.p0(i64 8, ptr nonnull %
  store ptr @P2a, ptr %P3, align 8, !tbaa !4               <
  br label %for.body                                              br label %for.body

[dtcxzyw]

IIRC it is a known issue :( As a workaround, you can compile it with -no-stack-coloring:

dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ clang -O0 tmp.c -w
dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ ./a.out 
0
dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ clang -Os tmp.c -w
dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ ./a.out 
1
dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ clang -Os tmp.c -w -mllvm -no-stack-coloring
dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ ./a.out 
0

[RSilicon]

IIRC it is a known issue :( As a workaround, you can compile it with -no-stack-coloring:

dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ clang -O0 tmp.c -w
dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ ./a.out 
0
dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ clang -Os tmp.c -w
dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ ./a.out 
1
dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ clang -Os tmp.c -w -mllvm -no-stack-coloring
dtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ ./a.out 
0

yeah, it's putting i and P3 at the same address
which they can't be

[dtcxzyw]

Related issue: #45725