[llvm-bugs] [Bug 56567] armv7-a thumb clang reorders ldr before the first inline asm in __attribute__((naked)) function

[LLVM Bugs via llvm-bugs]

Issue	56567
Summary	armv7-a thumb clang reorders ldr before the first inline asm in __attribute__((naked)) function
Labels	new issue
Assignees
Reporter	k15tfu

    Hi!

Compile the following code with `-O2 -fPIC -march=armv7-a -mthumb`:
```
void * this_ptr;
void (*call_enter_ptr)(void * this_);

__attribute__((naked))
void raw_call_enter() {
#if defined(__aarch64__)
    asm volatile(
        "stp x0, x1, [sp, #-16]!\n"
        // ...
        : : :
    );

    asm volatile("" : : : "memory"); // compiler barrier
    asm volatile(
        "ldr x0, %1\n"
        "blr %0\n"
        : : "r"(call_enter_ptr), "m"(this_ptr) : "x0"
    );

    asm volatile(
        // ...
        "ldp x0, x1, [sp], #16\n"
        : : :
    );

    asm volatile(
        "ret"
    );
#elif defined(__arm__)
    asm volatile(
        "push {r0-r3, r12, lr}\n"
        : : :
    );

    asm volatile("" : : : "memory"); // compiler barrier
    asm volatile(
        "ldr r0, %1\n"
        "blx %0\n"
        : : "r"(call_enter_ptr), "m"(this_ptr) : "r0"
    );

    asm volatile(
        "pop {r0-r3, r12, lr}\n"
        : : :
    );

    asm volatile(
        "bx lr"
    );
#endif
}
```

Output:
```
raw_call_enter():
        ldr     r0, .LCPI0_0
        ldr     r1, .LCPI0_1
        push.w  {r0, r1, r2, r3, r12, lr}  <-- and now r0 & r1 are invalid

.LPC0_0:
        add     r0, pc
.LPC0_1:
        add     r1, pc
        ldr     r0, [r0]
        ldr     r1, [r1]
        ldr     r2, [r0]
        ldr     r0, [r1]
        blx     r2

        pop.w   {r0, r1, r2, r3, r12, lr}

        bx      lr
.LCPI0_0:
.Ltmp1:
        .long   call_enter_ptr(GOT_PREL)-((.LPC0_0+4)-.Ltmp1)
.LCPI0_1:
.Ltmp2:
        .long   this_ptr(GOT_PREL)-((.LPC0_1+4)-.Ltmp2)
this_ptr:
        .long   0

call_enter_ptr:
        .long   0
```

armv7-a clang 11.0.1
https://godbolt.org/z/d9dMndvsj

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