ScheduleDAGEmit, TwoAddressLowering, and PHIElimination.
This switches the bulk of register copies to using COPY, but many less used
copyRegToReg calls remain.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108050 91177308-0d34-0410-b5e6-96231b3b80d8
into a utility routine, teach it how to update MachineLoopInfo, and
make use of it in MachineLICM to split critical edges on demand.
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addresses a longstanding deficiency noted in many FIXMEs scattered
across all the targets.
This effectively moves the problem up one level, replacing eleven
FIXMEs in the targets with eight FIXMEs in CodeGen, plus one path
through FastISel where we actually supply a DebugLoc, fixing Radar
7421831.
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Previously, LiveIntervalAnalysis would infer phi joins by looking for multiply
defined registers. That doesn't work if the phi join is implicitly defined in
all but one of the predecessors.
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into TargetOpcodes.h. #include the new TargetOpcodes.h
into MachineInstr. Add new inline accessors (like isPHI())
to MachineInstr, and start using them throughout the
codebase.
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non-landing pad basic block as the successor to a block that ends in an
unconditional jump will cause block folding to remove the added block as a
successor. Thus eventually removing it AND the landing pad entirely. Critical
edge splitting is an optimization, so we can safely turn it off when dealing
with landing pads.
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Tail duplication produces lots of identical phi nodes in different basic
blocks. Teach PHIElimination to reuse the join registers when lowering a phi
node that is identical to an already lowered node. This saves virtual
registers, and more importantly it avoids creating copies the the coalescer
doesn't know how to eliminate.
Teach LiveIntervalAnalysis about the phi joins with multiple uses.
This patch significantly reduces code size produced by -pre-regalloc-taildup.
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We want LiveVariables clients to use methods rather than accessing the
getVarInfo data structure directly. That way it will be possible to change the
LiveVariables representation.
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When splitting a critical edge, the registers live through the edge are:
- Used in a PHI instruction, or
- Live out from the predecessor, and
- Live in to the successor.
This allows the coalescer to eliminate even more phi joins.
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critical edges in PHIElimination.
This has a huge impact on regalloc performance, and we recover almost all of
the 10% compile time regression that edge splitting introduced.
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when LiveVariables is available.
The -split-phi-edges is now gone, and so is the hack to disable it when using
the local register allocator. The PHIElimination pass no longer has
LiveVariables as a prerequisite - that is what broke the local allocator.
Instead we do critical edge splitting when possible - that is when
LiveVariables is available.
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The local register allocator doesn't like it when LiveVariables is run.
We should also disable edge splitting under -O0, but that has to wait a bit.
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When splitting an edge after a machine basic block with fall-through, we
forgot to insert a jump instruction. Fix this by calling updateTerminator() on
the fall-through block when relevant.
Also be more precise in PHIElimination::isLiveIn.
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The BasicBlock associated with a MachineBasicBlock does not necessarily
correspond to the code in the MBB.
Don't insert a new IR BasicBlock when splitting critical edges. We are not
supposed to modify the IR during codegen, and we should be able to do just
fine with a NULL BB.
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- Edges are split before any phis are eliminated, so the code is SSA.
- Create a proper IR BasicBlock for the split edges.
- LiveVariables::addNewBlock now has same syntax as
MachineDominatorTree::addNewBlock. Algorithm calculates predecessor live-out
set rather than successor live-in set.
This feature still causes some miscompilations.
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Critical edges leading to a PHI node are split when the PHI source variable is
live out from the predecessor block. This help the coalescer eliminate more
PHI joins.
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previous cmp; a copy can not be inserted here if the copy insn also has
side effects. We don't have access to the attributes of copy insn here;
so just play safe by finding a safe locations for branch terminators.
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