Override try_[r]fold for RangeInclusive

[scottmcm]

Because the last item needs special handling, it seems that LLVM has trouble canonicalizing the loops in external iteration. With the override, it becomes obvious that the start==end case exits the loop (as opposed to the one after that exiting the loop in external iteration).

Demo adapted from #45222

#[no_mangle] pub fn foo3r(n: u64) -> u64 { let mut count = 0; (0..n).for_each(|_| { (0 ..= n).rev().for_each(|j| { count += j; }) }); count }

Current nightly ASM, 100 lines (https://play.rust-lang.org/?gist=f5674c702c6e2045c3aab5d03763e5f6&version=nightly&mode=release)

foo3r: pushq	%rbx .Lcfi0: .Lcfi1: testq	%rdi, %rdi je.LBB0_1 testb$1, %dil jne.LBB0_4 xorl	%eax, %eax xorl	%r8d, %r8d cmpq$1, %rdi jne.LBB0_11 jmp.LBB0_23 .LBB0_1: xorl	%eax, %eax popq	%rbx retq .LBB0_4: xorl	%r8d, %r8d movq$-1, %r9 xorl	%eax, %eax movq%rdi, %r11 xorl	%r10d, %r10d jmp.LBB0_5 .LBB0_8: addq	%r11, %rax movq%rsi, %r11 movq%rdx, %r10 .LBB0_5: cmpq	%r11, %r10 movl$1, %ecx cmovbq	%r9, %rcx cmoveq	%r8, %rcx testq	%rcx, %rcx movl$0, %esi movl$1, %edx je.LBB0_8 cmpq	$-1, %rcx jne.LBB0_9 leaq-1(%r11), %rsi movq%r10, %rdx jmp.LBB0_8 .LBB0_9: movl$1, %r8d cmpq$1, %rdi je.LBB0_23 .LBB0_11: xorl	%r9d, %r9d movq$-1, %r10 .LBB0_12: movq%rdi, %rsi xorl	%r11d, %r11d jmp.LBB0_13 .LBB0_16: addq	%rsi, %rax movq%rcx, %rsi movq%rbx, %r11 .LBB0_13: cmpq	%rsi, %r11 movl$1, %edx cmovbq	%r10, %rdx cmoveq	%r9, %rdx testq	%rdx, %rdx movl$0, %ecx movl$1, %ebx je.LBB0_16 cmpq	$-1, %rdx jne.LBB0_17 leaq-1(%rsi), %rcx movq%r11, %rbx jmp.LBB0_16 .LBB0_17: movq%rdi, %rcx xorl	%r11d, %r11d jmp.LBB0_18 .LBB0_21: addq	%rcx, %rax movq%rsi, %rcx movq%rbx, %r11 .LBB0_18: cmpq	%rcx, %r11 movl$1, %edx cmovbq	%r10, %rdx cmoveq	%r9, %rdx testq	%rdx, %rdx movl$0, %esi movl$1, %ebx je.LBB0_21 cmpq	$-1, %rdx jne.LBB0_22 leaq-1(%rcx), %rsi movq%r11, %rbx jmp.LBB0_21 .LBB0_22: addq$2, %r8 cmpq	%rdi, %r8 jne.LBB0_12 .LBB0_23: popq	%rbx retq .Lfunc_end0:

With this PR:

foo3r: testrcx, rcx je.LBB3_1 lear8, [rcx - 1] leardx, [rcx - 2] movrax, r8 mulrdx shldrdx, rax, 63 imulr8, r8 addr8, rcx subr8, rdx imulr8, rcx movrax, r8 ret .LBB3_1: xorr8d, r8d movrax, r8 ret

[rust-highfive]

r? @alexcrichton

(rust_highfive has picked a reviewer for you, use r? to override)

[alexcrichton]

@bors: r+

Thanks!

[bors]

📌 Commit 1b1e887 has been approved by alexcrichton