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]pubfnfoo3r(n:u64) -> u64{letmut 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, %rdije	.LBB0_1	testb$1, %diljne	.LBB0_4	xorl	%eax, %eax	xorl	%r8d, %r8d	cmpq$1, %rdijne	.LBB0_11jmp	.LBB0_23.LBB0_1:	xorl	%eax, %eax	popq	%rbx	retq.LBB0_4:	xorl	%r8d, %r8dmovq	$-1, %r9	xorl	%eax, %eaxmovq	%rdi, %r11	xorl	%r10d, %r10djmp	.LBB0_5.LBB0_8:	addq	%r11, %raxmovq	%rsi, %r11movq	%rdx, %r10.LBB0_5:	cmpq	%r11, %r10	movl$1, %ecx	cmovbq	%r9, %rcx	cmoveq	%r8, %rcx	testq	%rcx, %rcx	movl$0, %esi	movl$1, %edxje	.LBB0_8	cmpq	$-1, %rcxjne	.LBB0_9	leaq	-1(%r11), %rsimovq	%r10, %rdxjmp	.LBB0_8.LBB0_9:	movl$1, %r8d	cmpq$1, %rdije	.LBB0_23.LBB0_11:	xorl	%r9d, %r9dmovq	$-1, %r10.LBB0_12:movq	%rdi, %rsi	xorl	%r11d, %r11djmp	.LBB0_13.LBB0_16:	addq	%rsi, %raxmovq	%rcx, %rsimovq	%rbx, %r11.LBB0_13:	cmpq	%rsi, %r11	movl$1, %edx	cmovbq	%r10, %rdx	cmoveq	%r9, %rdx	testq	%rdx, %rdx	movl$0, %ecx	movl$1, %ebxje	.LBB0_16	cmpq	$-1, %rdxjne	.LBB0_17	leaq	-1(%rsi), %rcxmovq	%r11, %rbxjmp	.LBB0_16.LBB0_17:movq	%rdi, %rcx	xorl	%r11d, %r11djmp	.LBB0_18.LBB0_21:	addq	%rcx, %raxmovq	%rsi, %rcxmovq	%rbx, %r11.LBB0_18:	cmpq	%rcx, %r11	movl$1, %edx	cmovbq	%r10, %rdx	cmoveq	%r9, %rdx	testq	%rdx, %rdx	movl$0, %esi	movl$1, %ebxje	.LBB0_21	cmpq	$-1, %rdxjne	.LBB0_22	leaq	-1(%rcx), %rsimovq	%r11, %rbxjmp	.LBB0_21.LBB0_22:	addq$2, %r8	cmpq	%rdi, %r8jne	.LBB0_12.LBB0_23:	popq	%rbx	retq.Lfunc_end0:

With this PR:

foo3r:testrcx,rcxje	.LBB3_1lear8,[rcx-1]leardx,[rcx-2]movrax,r8mulrdxshldrdx,rax,63imulr8,r8addr8,rcxsubr8,rdximulr8,rcxmovrax,r8ret.LBB3_1:xorr8d,r8dmovrax,r8ret

[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