[AVR] illegal "LPM Rx, Z+" is generated on avr2 family devices

[benshi001]

LPMX is not avaliable on avr2, but for the following C code

void foo(int *p, int a) {
        static __flash const int arr[] = {123, 234, 456, 67};
        p[0] = arr[a];
}

Build it with command

clang a.c -O3 -Wall --target=avr -mmcu=at90s8515 -S

The following assembly is generated

foo:                                    ; @foo
; %bb.0:                                ; %entry
        lsl     r22
        rol     r23
        subi    r22, -lo8(foo.arr)
        sbci    r23, -hi8(foo.arr)
        mov     r30, r22
        mov     r31, r23
        lpm     r18, Z+
        lpm     r19, Z
        mov     r30, r24
        mov     r31, r25
        st      Z, r18
        std     Z+1, r19
        ret

However the lpm r19, Z belongs to feature LPMX and is illegal on AVR2 family.

[benshi001]

the LPM and ELPM instructions (in which R0 is the implicit destination) should be selected.

[benshi001]

The following devices are affected

def : Device<"at90s2313", FamilyAVR2, ELFArchAVR2>;
def : Device<"at90s2323", FamilyAVR2, ELFArchAVR2>;
def : Device<"at90s2333", FamilyAVR2, ELFArchAVR2>;
def : Device<"at90s2343", FamilyAVR2, ELFArchAVR2>;
def : Device<"attiny22", FamilyAVR2, ELFArchAVR2>;
def : Device<"attiny26", FamilyAVR2, ELFArchAVR2, [FeatureLPMX]>;
def : Device<"at86rf401", FamilyAVR2, ELFArchAVR25, [FeatureMOVW, FeatureLPMX]>;
def : Device<"at90s4414", FamilyAVR2, ELFArchAVR2>;
def : Device<"at90s4433", FamilyAVR2, ELFArchAVR2>;
def : Device<"at90s4434", FamilyAVR2, ELFArchAVR2>;
def : Device<"at90s8515", FamilyAVR2, ELFArchAVR2>;
def : Device<"at90c8534", FamilyAVR2, ELFArchAVR2>;
def : Device<"at90s8535", FamilyAVR2, ELFArchAVR2>;

[benshi001]

After https://reviews.llvm.org/D131844,

AVRExpandPseudo::expandLPMWELPMW is the only user of AVRExpandPseudo::scavengeGPR8, we need to check if we can eliminate that.

[benshi001]

fixed by https://github.com/llvm/llvm-project/commit/4fa9dc948226e374372537250d046924d348307e https://github.com/llvm/llvm-project/commit/2a6e39dbf84af4b3f8b31930fed786b3c56287f5 https://github.com/llvm/llvm-project/commit/acb4d143bdb75930eae8dc700e16e4950b8cc2c8