Dead Code Elimination Regression at -O3 (trunk vs 13.0.0)

[llvmbot]

Bugzilla Link	52580
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@anton-afanasyev

Extended Description

cat case.c
void foo(void);

static int b;
static int *e = &b;
static char a(char f) { return f < 0 ? f : 0; }
static char c(unsigned char f, int g) { return f >> g; }

int main() {
  int h = *e;
  *e = a(h);
  if (c(h, 1)){
    if (h)
      *e = 0;
    else
      foo();
  }
  c(0, 0);
}

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:
	xorl	%eax, %eax
	retq
.Lfunc_end0:
	.size	main, .Lfunc_end0-main
	.cfi_endproc
                                        # -- End function

clang-trunk -O3 -S -o /dev/stdout case.c
main:                                   # @main
	.cfi_startproc
# %bb.0:
	pushq	%rax
	.cfi_def_cfa_offset 16
	movl	b(%rip), %eax
	xorl	%ecx, %ecx
	testb	%al, %al
	movsbl	%al, %edx
	cmovsl	%edx, %ecx
	movl	%ecx, b(%rip)
	cmpb	$2, %dl
	jb	.LBB0_4
# %bb.1:
	testl	%eax, %eax
	je	.LBB0_3
# %bb.2:
	movl	$0, b(%rip)
.LBB0_4:
	xorl	%eax, %eax
	popq	%rcx
	.cfi_def_cfa_offset 8
	retq
.LBB0_3:
	.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 dc9b5550b2238d65bcaa937c412d51802d819aeb)
Target: x86_64-unknown-linux-gnu
Thread model: posix

Started with cfb6dfc

[llvmbot]

@llvm/issue-subscribers-clang-codegen

[fhahn]

It looks like this is still reproducible on current main. @anton-afanasyev is this an expected fallout of cfb6dfc?

[anton-afanasyev]

@fhahn Thanks for pointing this out! No, it is not expected. Assigned to myself.