The register scavenger maintains a DistanceMap that maps MI pointers to their
distance from the top of the current MBB. The DistanceMap is built
incrementally in forward() and in bulk in findFirstUse(). It is used by
scavengeRegister() to determine which candidate register has the longest
unused interval.
Unfortunately the DistanceMap contents can become outdated. The first time
scavengeRegister() is called, the DistanceMap is filled to cover the MBB. If
then instructions are inserted in the MBB (as they always are following
scavengeRegister()), the recorded distances are too short. This causes bad
behaviour in the included test case where a register use /after/ the current
position is ignored because findFirstUse() thinks is is /before/ the current
position. A "using an undefined register" assertion follows promptly.
The fix is to build a fresh DistanceMap at the top of scavengeRegister(), and
discard it after use. This means that DistanceMap is no longer needed as a
RegScavenger member variable, and forward() doesn't need to update it.
The fix then discloses issue number two in the same test case: The candidate
search in scavengeRegister() finds a CSR that has been saved in the prologue,
but is currently unused. It would be both inefficient and wrong to spill such
a register in the emergency spill slot. In the present case, the emergency
slot restore is placed immediately before the normal epilogue restore, leading
to a "Redefining a live register" assertion.
Fix number two: When scavengerRegister() stumbles upon an unused register that
is overwritten later in the MBB, return that register early. It is important
to verify that the register is defined later in the MBB, otherwise it might be
an unspilled CSR.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78650 91177308-0d34-0410-b5e6-96231b3b80d8
Now there is no special treatment of instructions that redefine part of a
super-register. Instead, the super-register is marked with <imp-use,kill> and
<imp-def>. For instance, from LowerSubregs on ARM:
subreg: CONVERTING: %Q1<def> = INSERT_SUBREG %Q1<undef>, %D1<kill>, 5
subreg: %D2<def> = FCPYD %D1<kill>, 14, %reg0, %Q1<imp-def>
subreg: CONVERTING: %Q1<def> = INSERT_SUBREG %Q1, %D0<kill>, 6
subreg: %D3<def> = FCPYD %D0<kill>, 14, %reg0, %Q1<imp-use,kill>, %Q1<imp-def>
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78466 91177308-0d34-0410-b5e6-96231b3b80d8
Verify that early clobber registers and their aliases are not used.
All changes to RegsAvailable are now done as a transaction so the order of
operands makes no difference.
The included test case is from PR4686. It has behaviour that was dependent on the order of operands.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78465 91177308-0d34-0410-b5e6-96231b3b80d8
- start support for new PEI w/reg alloc, allow running RS from emit{Pro,Epi}logue() target hooks.
- fix minor issue with recursion detection.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78318 91177308-0d34-0410-b5e6-96231b3b80d8
Allow imp-def and imp-use of anything in the scavenger asserts, just like the machine code verifier.
Allow redefinition of a sub-register of a live register.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77904 91177308-0d34-0410-b5e6-96231b3b80d8
Note, isUndef marker must be placed even on implicit_def def operand or else the scavenger will not ignore it. This is necessary because -O0 path does not use liveintervalanalysis, it treats implicit_def just like any other def.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74601 91177308-0d34-0410-b5e6-96231b3b80d8
The register allocator, when it allocates a register to a virtual register defined by an implicit_def, can allocate any physical register without worrying about overlapping live ranges. It should mark all of operands of the said virtual register so later passes will do the right thing.
This is not the best solution. But it should be a lot less fragile to having the scavenger try to track what is defined by implicit_def.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74518 91177308-0d34-0410-b5e6-96231b3b80d8
argument. Nothing was using it, and it set the MBB member without
calling enterBasicBlock, which was problematic.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61234 91177308-0d34-0410-b5e6-96231b3b80d8
- When scavenging a register, in addition to the spill, insert a restore before the first use.
- Abort if client is looking to scavenge a register even when a previously scavenged register is still live.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59697 91177308-0d34-0410-b5e6-96231b3b80d8
%r3<def> = OR %x3<kill>, %x3
We don't want to mark the %r3 as unused even though it's a sub-register of %x3.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48003 91177308-0d34-0410-b5e6-96231b3b80d8
PPC-64 doesn't work.) This also lowers the spilling of the CR registers so that
it uses a register other than the default R0 register (the scavenger scrounges
for one). A significant part of this patch fixes how kill information is
handled.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47863 91177308-0d34-0410-b5e6-96231b3b80d8