Re: [lra] patch mostly implementing pseudo live range split

[Jeff Law <law at redhat dot com>]

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On 11/29/11 15:03, Vladimir Makarov wrote:
> This patch contains a part of my several last weeks work on LRA.
> 
> 1. The major change is to add pseudo live range split
> transformation to the existing inheritance transformations.  The
> idea is to create a new split pseudo, add save/restore code using
> the split pseudo in EBB for a pseudo got hard register which
> intersects a few reload pseudos live ranges with high register
> pressure, and assign the original pseudo hard register to the split
> pseudo.  The transformation is undone if the split pseudo did not
> change his hard register or was not spilled in the assignment pass
> which is between the passes doing and undoing inheritance/split
> transformations.
> 
> This new functionality of LRA (pseudo range splitting) permits to 
> move a separate caller saves pass into inheritance/split 
> transformation pass.  This makes LRA smaller and a bit faster.
> 
> 2. The patch adds the code for correct update of debug insns for 
> inheritance/split transformations.  So I believe that now LRA
> deals with debug info not worse than reload pass.
> 
> 3. The patch rewrite the way of dealing with the secondary memory 
> moves in constraint pass of LRA.  Previously we generated
> secondary moves if macro SECONDARY_MEMORY_NEEDED says so.
> Unfortunately, the macro is usually defined inaccurately.
> Therefore now we emit secondary moves only if insn constraints are
> not satisfied (in other words we need reloads for given move).
> This change permitted to solve last degradations on GCC testsuite
> for x86-64/x86 in comparison when the reload pass is used.
> 
> 4. The patch also rewrites code for dealing with secondary memory 
> moves in PPC.  PPC port is single one allocating explicitly stack 
> slot for secondary memory of given mode through using macro 
> SECONDARY_MEMORY_NEEDED_RTX.  The patch rejects this approach for 
> LRA and uses a pseudo for secondary memory and this pseudo gets 
> memory as in standard mechanism for spilling in LRA.  This permits 
> reuse the slots allocated for secondary memory for other spilled 
> pseudo decreasing allocated stack slot size in some case.  This 
> change will permit to remove SECONDARY_MEMORY_NEEDED_RTX (as many 
> others) if LRA is in GCC finally.
> 
> 5. There are other small and insignificant changes in the patch
> mostly to fix some bugs and testsuite degradations.
> 
> The patch was successfully bootstrapped on x86/x86-64, ppc64, and 
> itanium.  Arm bootstrap is still going.
> 
> Committed to LRA branch as rev. 181820.
BTW, have you noticed the regressions creeping up on the lra branch
relative to the mainline?  We also need to merge in the api change to
pass in address spaces to base_reg_class.  I've avoided merging in
that specific change during my weekly merges.

I haven't looked at the overall framework you've built for splitting,
but the obvious question, can your framework handle splitting
unallocated pseudos on EBB boundaries?

jeff
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