Differential D110867 Diff 376576 llvm/test/CodeGen/X86/jump_sign.ll

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llvm/test/CodeGen/X86/jump_sign.ll

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	; CHECK-NEXT: cmovgl %ecx, %eax			; CHECK-NEXT: cmovgl %ecx, %eax
	; CHECK-NEXT: retl			; CHECK-NEXT: retl
	%cmp = icmp sgt i32 %a, %b			%cmp = icmp sgt i32 %a, %b
	%sub = sub nsw i32 %a, %b			%sub = sub nsw i32 %a, %b
	%cond = select i1 %cmp, i32 %b, i32 %sub			%cond = select i1 %cmp, i32 %b, i32 %sub
	ret i32 %cond			ret i32 %cond
	}			}

	; If EFLAGS is live-out, we can't remove cmp if there exists			; If EFLAGS is live-out, we can't remove cmp if there exists
				xbolva00Unsubmitted Not Done Reply Inline Actions cmp now removed xbolva00: cmp now removed
				MatzeBAuthorUnsubmitted Done Reply Inline Actions Good catch. So: I believe the comment to be outdated: When you look at r159888 adding the test: https://github.com/llvm/llvm-project/blob/bb36074047985cb476cadda464447b634972be2a/llvm/test/CodeGen/X86/jump_sign.ll#L110 the intention was that the cmp behind the sub is preserved. The single `CHECK` however doesn't really capture this and can match the `cmp` in bb.0 and the one in bb.1 I believe that SelectionDAG pattern matching improved in the meantime so nowadays the cmp is eliminated at that stage. The new version of the code is correct; you see that previously it used a `cmpl ecx, edx`, but `edx and eax` contain the same value and the sub in `bb.0` the only predecessor of `bb.1` is just the reverse operation and will produce the reverse flags. So we can indeed remove the cmp when we reverse the user flags `cmovle -> cmovl`. I accidentally put this test change onto the wrong commit in the stack. The test actually changes in D110862. MatzeB: Good catch. So: - I believe the comment to be outdated: - When you look at r159888 adding…
	; a swapped sub.			; a swapped sub.
	define i32 @func_l2(i32 %a, i32 %b) nounwind {			define i32 @func_l2(i32 %a, i32 %b) nounwind {
	; CHECK-LABEL: func_l2:			; CHECK-LABEL: func_l2:
	; CHECK: # %bb.0:			; CHECK: # %bb.0:
	; CHECK-NEXT: movl {{[0-9]+}}(%esp), %edx			; CHECK-NEXT: movl {{[0-9]+}}(%esp), %edx
	; CHECK-NEXT: movl {{[0-9]+}}(%esp), %ecx			; CHECK-NEXT: movl {{[0-9]+}}(%esp), %eax
	; CHECK-NEXT: movl %ecx, %eax			; CHECK-NEXT: movl %eax, %ecx
	; CHECK-NEXT: subl %edx, %eax			; CHECK-NEXT: subl %edx, %ecx
	; CHECK-NEXT: jne .LBB8_2			; CHECK-NEXT: jne .LBB8_2
	; CHECK-NEXT: # %bb.1: # %if.then			; CHECK-NEXT: # %bb.1: # %if.then
	; CHECK-NEXT: cmpl %ecx, %edx			; CHECK-NEXT: cmovll %ecx, %eax
	; CHECK-NEXT: cmovlel %ecx, %eax			; CHECK-NEXT: retl
	; CHECK-NEXT: .LBB8_2: # %if.else			; CHECK-NEXT: .LBB8_2: # %if.else
				; CHECK-NEXT: movl %ecx, %eax
	; CHECK-NEXT: retl			; CHECK-NEXT: retl
	%cmp = icmp eq i32 %b, %a			%cmp = icmp eq i32 %b, %a
	%sub = sub nsw i32 %a, %b			%sub = sub nsw i32 %a, %b
	br i1 %cmp, label %if.then, label %if.else			br i1 %cmp, label %if.then, label %if.else

	if.then:			if.then:
	%cmp2 = icmp sgt i32 %b, %a			%cmp2 = icmp sgt i32 %b, %a
	%sel = select i1 %cmp2, i32 %sub, i32 %a			%sel = select i1 %cmp2, i32 %sub, i32 %a
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