Regression: Inlined loops not fully evaluating with const-eable dependencies #101082
Description
I tried this code:
pub fn arr() -> usize { let values = [23, 16, 54, 3, 60, 9]; let mut acc = 0; for item in values { acc += item; } acc }I expected to see this happen: The loop should be inlined because values is const-known. For example, here is the generated assembly on Rust 1.63.0 (Godbolt) and Rust Beta (Godbolt):
example::arr: mov eax, 165 retInstead, this happened: On nightly, the loop is inlined. However, the entire function is not computed despite the stable and beta Rust inlining it. Here is the generated assembly on Nightly (Godbolt):
.LCPI0_0: .quad 23 .quad 16 .LCPI0_1: .quad 54 .quad 3 .LCPI0_2: .quad 60 .quad 9 example::arr: sub rsp, 72 movaps xmm0, xmmword ptr [rip + .LCPI0_0] movaps xmmword ptr [rsp], xmm0 movaps xmm0, xmmword ptr [rip + .LCPI0_1] movaps xmmword ptr [rsp + 16], xmm0 movaps xmm0, xmmword ptr [rip + .LCPI0_2] movaps xmmword ptr [rsp + 32], xmm0 mov qword ptr [rsp + 56], 6 xor ecx, ecx xor edx, edx jmp .LBB0_1 .LBB0_3: lea rdi, [rcx + 1] mov qword ptr [rsp + 48], rdi mov rdx, qword ptr [rsp + 8*rcx] mov esi, 1 mov rcx, rdi add rdx, rax test rsi, rsi je .LBB0_5 .LBB0_1: mov rax, rdx cmp rcx, 5 jbe .LBB0_3 xor esi, esi add rdx, rax test rsi, rsi jne .LBB0_1 .LBB0_5: add rsp, 72 retMeta
n/a - disclosed at usages
Keywords: const inline loop, const loop, const loop not evaluated
Relevant discord thread: https://discord.com/channels/273534239310479360/592856094527848449/1013050670942793808
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Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Category: This is a bug.Call for participation: An issue has been fixed and does not reproduce, but no test has been added.Issue: Problems and improvements with respect to performance of generated code.High priorityRelevant to the compiler team, which will review and decide on the PR/issue.Performance or correctness regression from stable to nightly.