https://bugs.llvm.org/show_bug.cgi?id=43515
Bug ID: 43515
Summary: trunc(x >> (bitwidth-1)) ^ 1 is not recognized as
bt+setae
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: lebedev...@gmail.com
CC: craig.top...@gmail.com, llvm-bugs@lists.llvm.org,
llvm-...@redking.me.uk, spatel+l...@rotateright.com
https://godbolt.org/z/jUiaJg
If we start with
int cmpge32_0(long a) {
return a>=0;
}
We get
shr rax, 63
xor eax, 1
But for less canonical
%n0 = and i64 %x, 9223372036854775808 # sign bit mask
%n1 = icmp eq i64 %n0, 0
%r = zext i1 %n1 to i32
we get seemingly-more-optimal
xor eax, eax
bt rdi, 63
setae al
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