The analysis will be needed by both the greedy register allocator and the
X86FloatingPoint pass. It only needs to be computed once when the CFG doesn't
change.
This pass is very fast, usually showing up as 0.0% wall time.
llvm-svn: 122832
Edge bundles is an annotation on the CFG that turns it into a bipartite directed
graph where each basic block is connected to an outgoing and an ingoing bundle.
These bundles are useful for identifying regions of the CFG for live range
splitting.
llvm-svn: 122301
the loop predecessors.
The register can be live-out from a predecessor without being live-in to the
loop header if there is a critical edge from the predecessor.
llvm-svn: 122123
Bypass loops have the current live range live through, but contain no uses or
defs. Splitting around a bypass loop can free registers for other uses inside
the loop by spilling the split range.
llvm-svn: 121871
Whenever splitting wants to insert a copy, it checks if the value can be
rematerialized cheaply instead.
Missing features:
- Delete instructions when all uses have been rematerialized.
- Truncate live ranges to the remaining uses after rematerialization.
llvm-svn: 118702
source, and let rewrite() clean it up.
This way, kill flags on the inserted copies are fixed as well during rewrite().
We can't just assume that all the copies we insert are going to be kills since
critical edges into loop headers sometimes require both source and dest to be
live out of a block.
llvm-svn: 117980
in SSAUpdaterImpl.h
Verifying live intervals revealed that the old method was completely wrong, and
we need an iterative approach to calculating PHI placemant. Fortunately, we have
MachineDominators available, so we don't have to compute that over and over
like SSAUpdaterImpl.h must.
Live-out values are cached between calls to mapValue() and computed in a greedy
way, so most calls will be working with very small block sets.
Thanks to Bob for explaining how this should work.
llvm-svn: 117599
proper SSA updating.
This doesn't cause MachineDominators to be recomputed since we are already
requiring MachineLoopInfo which uses dominators as well.
llvm-svn: 117598
Critical edges going into a loop are not as bad as critical exits. We can handle
them by splitting the critical edge, or by having both inside and outside
registers live out of the predecessor.
llvm-svn: 117423
the remainder register.
Example:
bb0:
x = 1
bb1:
use(x)
...
x = 2
jump bb1
When x is isolated in bb1, the inner part breaks into two components, x1 and x2:
bb0:
x0 = 1
bb1:
x1 = x0
use(x1)
...
x2 = 2
x0 = x2
jump bb1
llvm-svn: 117408
When a block has exactly two uses and the register is both live-in and live-out,
don't isolate the block. We would be inserting two copies, so we haven't really
made any progress.
If the live-in and live-out values separate into disconnected components after
splitting, we would be making progress. We can't detect that for now.
llvm-svn: 117169
An exit block with a critical edge must only have predecessors in the loop, or
just before the loop. This guarantees that the inserted copies in the loop
predecessors dominate the exit block.
llvm-svn: 117144
Jakob Stoklund Olesen
Benjamin Kramer