https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105617
Bug ID: 105617
Summary: Regression in code generation for _addcarry_u64()
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: already5chosen at yahoo dot com
Target Milestone: ---
It took many years until gcc caught up with MSVC and LLVM/clang in generation
of code for chains of Intel's _addcarry_u64() intrinsic calls. But your
finally managed to do it in gcc11.
Unfortunately, the luck didn't last for long.
void add4i(uint64_t dst[4], const uint64_t srcA[4], const uint64_t srcB[4])
{
unsigned char c;
unsigned long long r0; c = _addcarry_u64(0, srcA[0], srcB[0], &r0);
unsigned long long r1; c = _addcarry_u64(c, srcA[1], srcB[1], &r1);
unsigned long long r2; c = _addcarry_u64(c, srcA[2], srcB[2], &r2);
unsigned long long r3; c = _addcarry_u64(c, srcA[3], srcB[3], &r3);
dst[0] = r0;
dst[1] = r1;
dst[2] = r2;
dst[3] = r3;
}
gcc 11.1 -O2
add4i:
movq (%rdx), %rax
addq (%rsi), %rax
movq 8(%rsi), %rcx
movq %rax, %r8
adcq 8(%rdx), %rcx
movq 16(%rsi), %rax
adcq 16(%rdx), %rax
movq 24(%rdx), %rdx
adcq 24(%rsi), %rdx
movq %r8, (%rdi)
movq %rcx, 8(%rdi)
movq %rax, 16(%rdi)
movq %rdx, 24(%rdi)
ret
gcc 12.1 -O2
add4i:
movq (%rdx), %rax
movq 8(%rsi), %rcx
addq (%rsi), %rax
movq 16(%rsi), %r8
adcq 8(%rdx), %rcx
adcq 16(%rdx), %r8
movq %rax, %xmm1
movq 24(%rdx), %rdx
adcq 24(%rsi), %rdx
movq %r8, %xmm0
movq %rcx, %xmm3
movq %rdx, %xmm2
punpcklqdq %xmm3, %xmm1
punpcklqdq %xmm2, %xmm0
movups %xmm1, (%rdi)
movups %xmm0, 16(%rdi)
ret
What ... ?!
BTW, gcc 12.1 -O1 is still o.k.
