#3688 peep rule with notUsed not applied when expected

[Under4Mhz]

Using the below code with the following peep rule file, the peep rule is not applied as I would expect.

/// GPL 2.0 or later
#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>

#define reg_vram_access_address_high 14
#define BYTE_HI(x) ((x)>>8)

static volatile __sfr __at 0x98 VDPControlPort;

void vdu_interrupt_disable() { __asm di __endasm; }
void vdu_interrupt_enable() { __asm ei __endasm; }

///< Move memory pointer to specified address to set value
void vdu_address_set(uint16_t address) {

    vdu_interrupt_disable();

    VDPControlPort=address >> 14;
    VDPControlPort=reg_vram_access_address_high | 0x80;
    VDPControlPort=address;
    VDPControlPort=( BYTE_HI(address) & 0x3f ) | 0x40;

    vdu_interrupt_enable();

}

// sdcc -mz80 --fverbose-asm ./peep.c  -c && cat peep.c

with following peep rule:

replace {
    ld  c, a
    ld  b, #0x00
    ld  a, c

} by {
    ld  b, #0x00

} if notUsed('c')

I end up with the following snippet of asm:

;./peep.c:20: VDPControlPort=address >> 14;
    ld  a, h
    rlca
    rlca
    and a, #0x03
    ld  c, a
    ld  b, #0x00
    ld  a, c
    out (_VDPControlPort), a

Removing the "if notUsed('c')" I get the below I would expect using the notused:

;./peep.c:19: VDPControlPort=address >> 14;
    ld  a, h
    rlca
    rlca
    and a, #0x03
    ld  b, #0x00
    out (_VDPControlPort), a

The peep rule is not applied(with notused) as expected. Also the (peep) code generated doesn't seem to be useful in this case.

Removing either of the vdu_interrupt_* calls removes the extra b,c code.

SDCC : z80/sm83/z80n/mos6502 TD- 4.3.6 #14522 (Linux)

[Philipp Klaus Krause]

This issue is a bit complex, since it is about the interaction of tail call optimization with the peephole optimizer.
I have a fix that works for your example in the next branch in [r14553], but it won't make it into SDCC 4.4.0: The risk of this change breaking something is IMO too high, and the fixed issue just results in inefficient, not wrong code.

[Philipp Klaus Krause]

Fixed by merging next branch to trunk.