Subzero: More asm-verbose fixes.

Subzero: More asm-verbose fixes.

It turns out that code deleted in 9a05aea88a8d9484d5f0ea1f2eabf52ee5a3647f actually had a legitimate purpose, so it is added back, this time with more extensive comments justifying it.

Also, takes the instruction's IsDestNonKillable flag into account when updating the live register usage count (along with extra comments on why that is necessary).

Furthermore, removes an unnecessary assert that otherwise fails when --asm-verbose is used with --filetype=iasm or --filetype-obj.

BUG= none
R=jvoung@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=b82baf2f057520ed42c527bec8da58520eb03162

[Jim Stichnoth, 2015-05-26 23:59:13]

stichnot@chromium.org changed reviewers:
+ jvoung@chromium.org, kschimpf@google.com, mtrofin@chromium.org

[jvoung (off chromium), 2015-05-27 15:58:57]

https://codereview.chromium.org/1158113002/diff/1/src/IceCfgNode.cpp
File src/IceCfgNode.cpp (right):

https://codereview.chromium.org/1158113002/diff/1/src/IceCfgNode.cpp#newcode918
src/IceCfgNode.cpp:918: if (DecorateAsm && Dest->hasReg() &&
!I.isLastUse(I.getSrc(0)))
Just checking -- this checks !I.isLastUse(I.getSrc(0)), and the code used to
sort of do that too, via the && before decrementing, but now the decrement
happens in emitLiveRangesEnded regardless of Instr->isLastUse(Var); so it looks
like for assignments with Dest == Src(0), the count is bumped on the Dest and
then decremented on the Src(0) also (in emitLiveRangesEnded)?

[Jim Stichnoth, 2015-05-27 16:08:55]

https://codereview.chromium.org/1158113002/diff/1/src/IceCfgNode.cpp
File src/IceCfgNode.cpp (right):

https://codereview.chromium.org/1158113002/diff/1/src/IceCfgNode.cpp#newcode918
src/IceCfgNode.cpp:918: if (DecorateAsm && Dest->hasReg() &&
!I.isLastUse(I.getSrc(0)))
On 2015/05/27 15:58:56, jvoung wrote:
> Just checking -- this checks !I.isLastUse(I.getSrc(0)), and the code used to
> sort of do that too, via the && before decrementing, but now the decrement
> happens in emitLiveRangesEnded regardless of Instr->isLastUse(Var); so it
looks
> like for assignments with Dest == Src(0), the count is bumped on the Dest and
> then decremented on the Src(0) also (in emitLiveRangesEnded)?

Sorry - I discovered that problem yesterday and uploaded a new patch this
morning that does indeed guard the decrement with an isLastUse() check.

[jvoung (off chromium), 2015-05-27 16:54:10]

lgtm

[Jim Stichnoth, 2015-05-27 17:41:12]

Committed patchset #2 (id:20001) manually as
b82baf2f057520ed42c527bec8da58520eb03162 (presubmit successful).