canTailDuplicate accepts two blocks and returns true if the first can be
duplicated into the second successfully. Use this function to
encapsulate the heuristic.
llvm-svn: 276062
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
When a block is tail-duplicated, the PHI nodes from that block are
replaced with appropriate COPY instructions. When those PHI nodes
contained use operands with subregisters, the subregisters were
dropped from the COPY instructions, resulting in incorrect code.
Keep track of the subregister information and use this information
when remapping instructions from the duplicated block.
Differential Revision: http://reviews.llvm.org/D19337
llvm-svn: 267583
This is in preparation for tail duplication during block placement. See D18226.
This needs to be a utility class for 2 reasons. No passes may run after block
placement, and also, tail-duplication affects subsequent layout decisions, so
it must be interleaved with placement, and can't be separated out into its own
pass. The original pass is still useful, and now runs by delegating to the
utility class.
llvm-svn: 265842
