[llvm-bugs] [Bug 52261] New: Dead Code Elimination Regression at -O3 (trunk vs 13.0.0)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=52261

            Bug ID: 52261
           Summary: Dead Code Elimination Regression at -O3 (trunk vs
                    13.0.0)
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: theodort at inf.ethz.ch
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

cat test.c    
void foo(void);
void bar(void);

static char b = 2;
static int d = -2, e;

static int a(int f, int g) { return (g & -g) < 0 ? f : f - g; }

int main() {
  d = 0;
  d = b;
  bar();
  e = a(0, 0);
  if (a(-2, d) > 1)
    foo();
}


13.0.0 at -O3 can eliminate the call to foo but trunk cannot:

clang-13 -O3 -S -o /dev/stdout test.c
...
main:                                   # @main
        .cfi_startproc
# %bb.0:
        pushq   %rax
        .cfi_def_cfa_offset 16
        movb    $1, d(%rip)
        callq   bar
        xorl    %eax, %eax
        popq    %rcx
        .cfi_def_cfa_offset 8
        retq


clang-trunk -O3 -S -o /dev/stdout case13_clean.c
...
main:                                   # @main
        .cfi_startproc
# %bb.0:
        pushq   %rax
        .cfi_def_cfa_offset 16
        movb    $1, d(%rip)
        callq   bar
        movzbl  d(%rip), %eax
        leal    -2(,%rax,4), %ecx
        movl    %eax, %edx
        shll    $2, %edx
        movl    $2, %esi
        subl    %edx, %esi
        testl   %esi, %ecx
        js      .LBB0_3
# %bb.1:
        leal    -1(,%rax,4), %eax
        cmpl    $-3, %eax
        jg      .LBB0_3
# %bb.2:
        callq   foo
.LBB0_3:
        xorl    %eax, %eax
        popq    %rcx
        .cfi_def_cfa_offset 8
        retq

clang-trunk -v
clang version 14.0.0 (https://github.com/llvm/llvm-project.git
eda2ebd7807376829eb880c39623f364b438971f)
Target: x86_64-unknown-linux-gnu
Thread model: posix


https://github.com/llvm/llvm-project/commit/da210f5d3425e8877ceabaf6ed3483d52cbd7448
introduced this regression

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