Efficiently handle a long multiplication by a constant. For this testcase:
long %test(long %X) {
%Y = mul long %X, 123
ret long %Y
}
we used to generate:
test:
sub %ESP, 12
mov DWORD PTR [%ESP + 8], %ESI
mov DWORD PTR [%ESP + 4], %EDI
mov DWORD PTR [%ESP], %EBX
mov %ECX, DWORD PTR [%ESP + 16]
mov %ESI, DWORD PTR [%ESP + 20]
mov %EDI, 123
mov %EBX, 0
mov %EAX, %ECX
mul %EDI
imul %ESI, %EDI
add %ESI, %EDX
imul %ECX, %EBX
add %ESI, %ECX
mov %EDX, %ESI
mov %EBX, DWORD PTR [%ESP]
mov %EDI, DWORD PTR [%ESP + 4]
mov %ESI, DWORD PTR [%ESP + 8]
add %ESP, 12
ret
Now we emit:
test:
mov %EAX, DWORD PTR [%ESP + 4]
mov %ECX, DWORD PTR [%ESP + 8]
mov %EDX, 123
mul %EDX
imul %ECX, %ECX, 123
add %ECX, %EDX
mov %EDX, %ECX
ret
Which, incidently, is substantially nicer than what GCC manages:
T:
sub %esp, 8
mov %eax, 123
mov DWORD PTR [%esp], %ebx
mov %ebx, DWORD PTR [%esp+16]
mov DWORD PTR [%esp+4], %esi
mov %esi, DWORD PTR [%esp+12]
imul %ecx, %ebx, 123
mov %ebx, DWORD PTR [%esp]
mul %esi
mov %esi, DWORD PTR [%esp+4]
add %esp, 8
lea %edx, [%ecx+%edx]
ret
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12692 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed