dead function call is not removed in branch comparing global variable addresses

[thetheodor]

Bugzilla Link	49434
Version	trunk
OS	Linux
CC	@ttheodor

Extended Description

~/llvm-project/build/bin/clang -v
clang version 13.0.0 (https://github.com/llvm/llvm-project.git d2000b4)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/theo/llvm-project/build/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0
Found candidate GCC installation: /usr/lib64/gcc/x86_64-pc-linux-gnu/10.2.0
Selected GCC installation: /usr/lib64/gcc/x86_64-pc-linux-gnu/10.2.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
Found CUDA installation: /opt/cuda, version 11.2

---

cat test.c
char a, b[2];

extern void foo (void);
int main() {
char *c = &a, *d = &b[1];
if (c == d)
foo();
return 0;
}

---

~/llvm-project/build/bin/clang -O3 -S -o /dev/stdout test.c
.text
.file "test.c"
.globl main # -- Begin function main
.p2align 4, 0x90
.type main,@function
main: # @​main
.cfi_startproc

%bb.0: # %entry

movl	$b+1, %eax
cmpq	$a, %rax
jne	.LBB0_2

%bb.1: # %if.then

pushq	%rax
.cfi_def_cfa_offset 16
callq	foo
addq	$8, %rsp
.cfi_def_cfa_offset 8

.LBB0_2: # %if.end
xorl %eax, %eax
retq
.Lfunc_end0:
.size main, .Lfunc_end0-main
.cfi_endproc
# -- End function
.type a,@object # @​a
.bss
.globl a
a:
.byte 0 # 0x0
.size a, 1

.type	b,@object                       # @​b
.globl	b

b:
.zero 2
.size b, 2

.ident	"clang version 13.0.0 (https://github.com/llvm/llvm-project.git d2000b45d033c06dc7973f59909a0ad12887ff51)"
.section	".note.GNU-stack","",@progbits
.addrsig
.addrsig_sym a
.addrsig_sym b

---

if *d = &b[1]; is replaced with *d=b, the dead branch is properly DCE'd.