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TailDuplicator: Remove live-in updating logic

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This logic was introduced in r157663 and does not make any sense to me.
The motivating example in rdar://11538365 looks like this:

This is the tail:
BB#16: derived from LLVM BB %if.end68
    Live Ins: %R0 %R4 %R5
    Predecessors according to CFG: BB#15 BB#5
        tBLXi pred:14, pred:%noreg, <ga:@CFRelease>, %R0<kill>, <regmask>, %LR<imp-def,dead>, %SP<imp-use>, %SP<imp-def>
        t2B <BB#20>, pred:14, pred:%noreg
    Successors according to CFG: BB#20

This is the predBB:
BB#5:
    Live Ins: %R5
    Predecessors according to CFG: BB#4
        %R4<def> = t2MOVi 0, pred:14, pred:%noreg, opt:%noreg
        t2B <BB#16>, pred:14, pred:%noreg
    Successors according to CFG: BB#16

However this is invalid machine code to begin with, if %R0 is live-in to
BB#16 then it must be live-in to BB#5 as well if BB#5 does not define
it.  We should not need logic to retroactively fix broken machine code
and in fact the example from r157663 passes cleanly with the code
removed and I do not see any (newly) failing tests with the machine
verifier enabled.

Differential Revision: http://reviews.llvm.org/D22031

llvm-svn: 274655
This commit is contained in:
Matthias Braun 2016-07-06 18:55:10 +00:00
parent affa1c30c2
commit f16acbd2f9
2 changed files with 0 additions and 19 deletions
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1
llvm/include/llvm/CodeGen/TailDuplicator.h
View File

@ -33,7 +33,6 @@ class TailDuplicator {
const MachineBranchProbabilityInfo *MBPI;
const MachineModuleInfo *MMI;
MachineRegisterInfo *MRI;
std::unique_ptr<RegScavenger> RS;
bool PreRegAlloc;
// A list of virtual registers for which to update SSA form.

18
llvm/lib/CodeGen/TailDuplicator.cpp
View File

@ -67,10 +67,6 @@ void TailDuplicator::initMF(MachineFunction &MF, const MachineModuleInfo *MMIin,
assert(MBPI != nullptr && "Machine Branch Probability Info required");
PreRegAlloc = MRI->isSSA();
RS.reset();
if (MRI->tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF))
RS.reset(new RegScavenger());
}
static void VerifyPHIs(MachineFunction &MF, bool CheckExtra) {
@ -770,20 +766,6 @@ bool TailDuplicator::tailDuplicate(MachineFunction &MF, bool IsSimple,
// Remove PredBB's unconditional branch.
TII->RemoveBranch(*PredBB);
if (RS && !TailBB->livein_empty()) {
// Update PredBB livein.
RS->enterBasicBlock(*PredBB);
if (!PredBB->empty())
RS->forward(std::prev(PredBB->end()));
for (const auto &LI : TailBB->liveins()) {
if (!RS->isRegUsed(LI.PhysReg, false))
// If a register is previously livein to the tail but it's not live
// at the end of predecessor BB, then it should be added to its
// livein list.
PredBB->addLiveIn(LI);
}
}
// Clone the contents of TailBB into PredBB.
DenseMap<unsigned, RegSubRegPair> LocalVRMap;
SmallVector<std::pair<unsigned, RegSubRegPair>, 4> CopyInfos;