https://bugs.llvm.org/show_bug.cgi?id=41272
Bug ID: 41272
Summary: Failure to hoist constant mask out of loop
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
https://godbolt.org/z/YXhpEv
#include <stdint.h>
uint64_t sum_mask32(const uint64_t *p, int len) {
uint64_t sum = 0;
for(int i = 0; i < len; i++) {
sum += *p++ & 0x80008000;
}
return sum;
}
With clang -Os the loop kernel is:
.LBB0_4: # =>This Inner Loop Header: Depth=1
movq (%rdi,%rdx,8), %rsi
andl $-2147450880, %esi # imm = 0x80008000
addq %rsi, %rax
incq %rdx
cmpl %edx, %ecx
jne .LBB0_4
retq
With clang -O3 the unrolled kernel is even worse:
.LBB0_9: # =>This Inner Loop Header: Depth=1
movq (%rdi), %rcx
movq 8(%rdi), %rdx
andl $-2147450880, %ecx # imm = 0x80008000
addq %rax, %rcx
andl $-2147450880, %edx # imm = 0x80008000
addq %rcx, %rdx
movq 16(%rdi), %rcx
andl $-2147450880, %ecx # imm = 0x80008000
addq %rdx, %rcx
movq 24(%rdi), %rax
addq $32, %rdi
andl $-2147450880, %eax # imm = 0x80008000
addq %rcx, %rax
addl $4, %r9d
jne .LBB0_9
testl %r8d, %r8d
je .LBB0_7
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