[MIPS] Failure to ever optimize out function prologue and epilogue

[GabrielRavier]

Bugzilla Link	48982
Version	trunk
OS	Linux

Extended Description

void f(){}

With -O3, GCC generates this:

f():
jrc $31

LLVM generates this:

f():
daddiu $sp, $sp, -16
sd $ra, 8($sp) # 8-byte Folded Spill
sd $fp, 0($sp) # 8-byte Folded Spill
move $fp, $sp
move $sp, $fp
ld $fp, 0($sp) # 8-byte Folded Reload
ld $ra, 8($sp) # 8-byte Folded Reload
jr $ra
daddiu $sp, $sp, 16

[sdardis]

What are the command line options used to to compile the test case? Checking with godbolt I can't reproduce the issue. I can only partially reproduce the LLVM output with -O0, but that produces a nop in the delay slot of the jr instruction.

[GabrielRavier]

What are the command line options used to to compile the test case? Checking with godbolt I can't reproduce the issue. I can only partially reproduce the LLVM output with -O0, but that produces a nop in the delay slot of the jr instruction.

I can reproduce it on Godbolt with -target mips64el -O3: https://godbolt.org/z/qM4K6TW4T

[brad0]

cc @yingopq @wzssyqa