[llvm-commits] [llvm] r66976 - in /llvm/trunk: lib/CodeGen/PHIElimination.cpp lib/Transforms/Scalar/CodeGenPrepare.cpp test/CodeGen/X86/2009-03-13-PHIElimBug.ll test/CodeGen/X86/split-eh-lpad-edges.ll

[Evan Cheng]

On Mar 16, 2009, at 12:39 AM, Duncan Sands wrote:

> Hi Evan,
>
>>>       %reg1031<def> = MOV32rr %EAX
>>>       EH_LABEL 2
>>>       %reg1025<def> = MOV32rr %reg1031  <= Invoke result, not an
>>> EH_LABEL
>>>       JMP mbb<entry.cont_crit_edge,0xa11af90>
>>>
>>> So in this case the logic bails out, putting the copy at the end of
>>> the BB,
>>> even though it might still need to be before the invoke.
>>
>> Something seems wrong with this. Who inserted the copy? The copy from
>> EAX to reg1031 is the copy lowered by isel. Is PHI elimination
>> inserting the copy from reg1031 to reg1025? Then it should have done
>> the right thing.
>
> I'm not sure where it's coming from (see testcase below).  By the  
> way, what
> do you think of the patch I sent?  It's more efficient in the common  
> case of
> an invoke with one def/use of SrcReg in the basic block, but less  
> efficient
> when there is more than one def/use because it has to walk more of  
> the basic
> block.

That looks good unless there is some assumptions of placement of  
copies introduced by PHI elim (I surely hope not). This needs to go  
through lots of testing.

Also, I really want to know where the above mentioned copy copies  
from. But I haven't found the time to look at it.

Evan

>
> Ciao,
>
> Duncan.
>
> Run: llc -march=x86 -f phi.bc
>
> If I break on WalkPassEHTryRange, then the first time I hit the  
> breakpoint
> I see such a register copy after the EH_LABEL.  This is the MBB for  
> "cont",
> and it is trying to find a place to put the copy for the phi node in  
> the
> landing pad.
>
> declare i32 @f()
>
> declare i32 @g()
>
> define i32 @phi() {
> entry:
> 	%a = call i32 @f()		; <i32> [#uses=1]
> 	%b = invoke i32 @g()
> 			to label %cont unwind label %lpad		; <i32> [#uses=1]
>
> cont:		; preds = %entry
> 	%x = phi i32 [ %b, %entry ]		; <i32> [#uses=0]
> 	%aa = call i32 @f()		; <i32> [#uses=1]
> 	%bb = invoke i32 @g()
> 			to label %cont2 unwind label %lpad		; <i32> [#uses=1]
>
> cont2:		; preds = %cont
> 	%xx = phi i32 [ %bb, %cont ]		; <i32> [#uses=1]
> 	ret i32 %xx
>
> lpad:		; preds = %cont, %entry
> 	%y = phi i32 [ %a, %entry ], [ %aa, %cont ]		; <i32> [#uses=1]
> 	ret i32 %y
> }