Expand 64-bit shifts more optimally if we know that the high bit of the
shift amount is one or zero. For example, for:
long long foo1(long long X, int C) {
return X << (C|32);
}
long long foo2(long long X, int C) {
return X << (C&~32);
}
we get:
_foo1:
movb $31, %cl
movl 4(%esp), %edx
andb 12(%esp), %cl
shll %cl, %edx
xorl %eax, %eax
ret
_foo2:
movb $223, %cl
movl 4(%esp), %eax
movl 8(%esp), %edx
andb 12(%esp), %cl
shldl %cl, %eax, %edx
shll %cl, %eax
ret
instead of:
_foo1:
subl $4, %esp
movl %ebx, (%esp)
movb $32, %bl
movl 8(%esp), %eax
movl 12(%esp), %edx
movb %bl, %cl
orb 16(%esp), %cl
shldl %cl, %eax, %edx
shll %cl, %eax
xorl %ecx, %ecx
testb %bl, %bl
cmovne %eax, %edx
cmovne %ecx, %eax
movl (%esp), %ebx
addl $4, %esp
ret
_foo2:
subl $4, %esp
movl %ebx, (%esp)
movb $223, %cl
movl 8(%esp), %eax
movl 12(%esp), %edx
andb 16(%esp), %cl
shldl %cl, %eax, %edx
shll %cl, %eax
xorl %ecx, %ecx
xorb %bl, %bl
testb %bl, %bl
cmovne %eax, %edx
cmovne %ecx, %eax
movl (%esp), %ebx
addl $4, %esp
ret
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@30506 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed