[llvm-bugs] [Bug 52592] New: Dead Code Elimination Regression at -O3 (trunk vs 13.0.0)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=52592

            Bug ID: 52592
           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 case.c
void bar(void);
void foo(void);

static char b = 1;
static int c;

static int d(int e) { return e; }

int main() {
  b = 0;
  bar();
  c = d(2048);
  if (!((((0 == c || b) && 1) ^ 2)% 5))
  {
    d(0);
    foo();
  }
}

trunk cannot eliminate the call to foo but 13.0.0 can:

clang-13.0.0 -O3 -S -o /dev/stdout case.c
main:                                   # @main
        .cfi_startproc
# %bb.0:
        pushq   %rax
        .cfi_def_cfa_offset 16
        callq   bar
        xorl    %eax, %eax
        popq    %rcx
        .cfi_def_cfa_offset 8
        retq
.Lfunc_end0:


clang-trunk -O3 -S -o /dev/stdout case.c
main:                                   # @main
        .cfi_startproc
# %bb.0:
        pushq   %rax
        .cfi_def_cfa_offset 16
        movb    $1, b(%rip)
        callq   bar
        movzbl  b(%rip), %eax
        xorl    $1, %eax
        orl     $2, %eax
        imull   $-858993459, %eax, %eax         # imm = 0xCCCCCCCD
        cmpl    $858993459, %eax                # imm = 0x33333333
        jbe     .LBB0_1
# %bb.2:
        xorl    %eax, %eax
        popq    %rcx
        .cfi_def_cfa_offset 8
        retq
.LBB0_1:
        .cfi_def_cfa_offset 16
        callq   foo
        xorl    %eax, %eax
        popq    %rcx
        .cfi_def_cfa_offset 8
        retq
.Lfunc_end0:


clang-trunk -v
clang version 14.0.0 (https://github.com/llvm/llvm-project
38ed1db7e8740fce236d1893ff9e20cc22ef0ada)
Target: x86_64-unknown-linux-gnu
Thread model: posix


Started with
https://github.com/llvm/llvm-project/commit/e7249e4acf3cf9438d6d9e02edecebd5b622a4dc

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