[PATCH] Remove redundent register mov by improving TwoAddressInstructionPass

[Wei Mi]

REPOSITORY
  rL LLVM

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Comment at: lib/CodeGen/TwoAddressInstructionPass.cpp:314-315
@@ -311,1 +313,4 @@
 
+// getSingleDef -- return the MachineInstr* if it is the single def of the Reg
+// in current BB.
+static MachineInstr* getSingleDef(unsigned Reg, MachineBasicBlock *BB,
----------------
chandlerc wrote:
> Please use our modern doxygen comment style for new code. (I know a bunch of old code doesn't)
> 
> http://llvm.org/docs/CodingStandards.html#doxygen-use-in-documentation-comments
Fixed.

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Comment at: lib/CodeGen/TwoAddressInstructionPass.cpp:340-341
@@ +339,4 @@
+  unsigned TmpReg = FromReg;
+  // We set Length to 3 for now, which covers the common cases we see. Set the
+  // Length limit is to avoid endless searching in a copy chain loop.
+  int Length = 3;
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chandlerc wrote:
> It would be good to document your idea for how to handle this more generally in a FIXME here and maybe file a PR to track it?
FIXME added. File a PR here: http://llvm.org/bugs/show_bug.cgi?id=22689

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Comment at: test/CodeGen/X86/twoaddr-coalesce-3.ll:22
@@ +21,3 @@
+; CHECK-LABEL: foo:
+; CHECK: [[LOOP1:.LBB0_[0-9]+]]: # %for.body
+; CHECK-NOT: mov
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qcolombet wrote:
> Like I said, you shouldn’t use basic block labels, but rely on branch instruction on other block.
> E.g, on my machine the label looks like this: LBB0_…, i.e., no leading ‘.’.
> 
> So, what I was saying was to use something like:
> 
> ; End of the first block.
> CHECK: jp
> ; We enter the loop
> CHECK loop boby
> ; The loop body is done
> CHECK jp
Yes, I understand your concern. However using branch instruction in previous block as boundary will introduce extra code in loop preheader, including mov. Like the following movl total(%rip), ..., I can make the test right, but it introduces extra complexity. 

	jle	.LBB0_4
# BB#1:                                 # %for.body.lr.ph
	xorl	%edx, %edx
	movl	total(%rip), %ecx
	.align	16, 0x90
.LBB0_2:                                # %for.body
                                        # =>This Inner Loop Header: Depth=1
	movl	%edx, %esi
	shrl	$31, %esi
	addl	%edx, %esi
	sarl	%esi
	addl	%esi, %ecx
	incl	%edx
	cmpl	%eax, %edx
	jl	.LBB0_2

Do you like CHECK: [[LOOP:[.]?LBB0_[0-9]+]]; ? If not, I will follow your way to use last branch as the boundary.

http://reviews.llvm.org/D7806

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