https://bugs.llvm.org/show_bug.cgi?id=38938
Bug ID: 38938
Summary: [X86][BMI] Pointer arithmetic prevents BEXTR lowering
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: llvm-...@redking.me.uk
CC: craig.top...@gmail.com, lebedev...@gmail.com,
llvm-bugs@lists.llvm.org, spatel+l...@rotateright.com
void update(int *counts, uint64_t *key) {
counts[(*key++ >> 21) & ((1 << 10) - 1)]++;
}
define void @update(i32* %a0, i64* %a1) {
%1 = load i64, i64* %a1, align 8
%2 = lshr i64 %1, 21
%3 = and i64 %2, 1023
%4 = getelementptr inbounds i32, i32* %a0, i64 %3
%5 = load i32, i32* %4, align 4
%6 = add nsw i32 %5, 1
store i32 %6, i32* %4, align 4
ret void
}
llc -mcpu=btver2
update:
movq (%rsi), %rax
shrq $19, %rax
andl $4092, %eax # imm = 0xFFC
incl (%rdi,%rax)
retq
Converting the index into a pointer stops bextr from being used, otherwise we'd
be able to lower to something like:
update:
movl $2581, %eax # imm = 0xA15
bextrl %eax, (%rsi), %eax
incl (%rdi,%rax,4)
retq
--
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