[GlobalISel][AArch64] Calling convention for small arguments passed on stack incorrect on big-endian targets

[ostannard]

Bugzilla Link	35361
Version	trunk
OS	Linux
Depends On	#26535
CC	@qcolombet

Extended Description

Global-isel generates incorrect code when targeting big-endian AArch64 for this code:
int foo(int x0, int x1, int x2, int x3, int x4, int x5, int x6, int x7,
int stack1) {
return stack1;
}

int main() {
int ret = foo(0,1,2,3,4,5,6,7,8);
printf("%d\n", ret);
}

Global isel thinks that the incoming value of stack1 is stored in bytes [0,4) above SP, but for big-endian targets this should be in bytes [4,8):

// /work/llvm/build/bin/clang --target=aarch64-arm-none-eabi -march=armv8-a -c callees.cpp -O0 -Wall -std=c++11 -mllvm -global-isel=true -mllvm -global-isel-abort=0 -mbig-endian -o - -S
_Z3fooiiiiiiiii: // @​_Z3fooiiiiiiiii
// BB#0: // %entry
sub sp, sp, #​48 // =48
ldr w8, [sp, #​48] // <= Should be [sp, #​52]
str w0, [sp, #​44]
str w1, [sp, #​40]
str w2, [sp, #​36]
str w3, [sp, #​32]
str w4, [sp, #​28]
str w5, [sp, #​24]
str w6, [sp, #​20]
str w7, [sp, #​16]
str w8, [sp, #​12]
ldr w0, [sp, #​12]
add sp, sp, #​48 // =48
ret

[ostannard]

assigned to @aemerson

[qcolombet]

Hi Amara, could you take a look?
Thanks.

[aemerson]

GISel big endian will be disabled until #26535 is resolved.

[aemerson]

Closing as we're not going to implement BE support for AArch64 GISel any time soon. This has been worked around via a fallback instead.

[llvmbot]

@llvm/issue-subscribers-backend-aarch64