block with its unique predecessor. Change the code to assert if that is not
the case, instead of trying to handle situations where the block has
multiple predecessors.
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Dan was trying to catch the case where a basic block ends with a conditional
branch to the fall-through block. In this case, all the instructions have
been moved out of FromBBI, leaving it empty. It cannot end with a
conditional branch. As the existing comment indicates, it will always fall
through to the next block. If the block already had the next block (NBB)
listed as a successor, the preceding loop has a check for that and does not
remove it. Thus, we need to check and add the successor only when it is
not already listed.
With Dan's change, the empty block often ends up with the fall-through
successor listed twice. This exposed the problem in pr4195, where
CodePlacementOpt did not handle the same predecessor listed more than once.
It is also at least partially responsible for pr4202 and probably a similar
issue with Thumb branches being out of range.
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allow it to have multiple CFG edges to that block. This is needed
to allow MachineBasicBlock::isOnlyReachableByFallthrough to work
correctly. This fixes PR4126.
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Where previously LLVM might emit code like this:
ucomisd %xmm1, %xmm0
setne %al
setp %cl
orb %al, %cl
jne .LBB4_2
it now emits this:
ucomisd %xmm1, %xmm0
jne .LBB4_2
jp .LBB4_2
It has fewer instructions and uses fewer registers, but it does
have more branches. And in the case that this code is followed by
a non-fallthrough edge, it may be followed by a jmp instruction,
resulting in three branch instructions in sequence. Some effort
is made to avoid this situation.
To achieve this, X86ISelLowering.cpp now recognizes FCMP_OEQ and
FCMP_UNE in lowered form, and replace them with code that emits
two branches, except in the case where it would require converting
a fall-through edge to an explicit branch.
Also, X86InstrInfo.cpp's branch analysis and transform code now
knows now to handle blocks with multiple conditional branches. It
uses loops instead of having fixed checks for up to two
instructions. It can now analyze and transform code generated
from FCMP_OEQ and FCMP_UNE.
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handled correctly, and change a few SmallVector uses to use
size 0 to more clearly reflect their intent.
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MachineMemOperands. The pools are owned by MachineFunctions.
This drastically reduces the number of calls to malloc/free made
during the "Emit" phase of scheduling, as well as later phases
in CodeGen. Combined with other changes, this speeds up the
"instruction selection" phase of CodeGen by 10% in some cases.
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that it is cheap and efficient to get.
Move a variety of predicates from TargetInstrInfo into
TargetInstrDescriptor, which makes it much easier to query a predicate
when you don't have TII around. Now you can use MI->getDesc()->isBranch()
instead of going through TII, and this is much more efficient anyway. Not
all of the predicates have been moved over yet.
Update old code that used MI->getInstrDescriptor()->Flags to use the
new predicates in many places.
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1. Consider all possible ifcvt cases at once. No longer restricted to bottom
up iterative approach.
2. Sort all possible cases based on a cost function. Perform the most profitable
ones first invalidate others that target the same blocks.
3. Fixed a number of bugs related to block duplication.
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