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Unfortunately the DistanceMap contents can become outdated.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.
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and short. Well, it's kinda short. Definitely nasty and brutish.
The front-end generates the register/unregister calls into the SjLj runtime,
call-site indices and landing pad dispatch. The back end fills in the LSDA
with the call-site information provided by the front end. Catch blocks are
not yet implemented.
Built on Darwin and verified no llvm-core "make check" regressions.
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MERGE_VALUES nodes. Replacing the result values with the
operands in one MERGE_VALUES node may cause another
MERGE_VALUES node be CSE'd with the first one, and bring
its uses along, so that the first one isn't dead, as this
code expects. Fix this by iterating until the node is
really dead. This fixes PR4699.
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This definitely slows down asm output so put it under an -asm-exuberant
flag.
This information is useful when doing static analysis of performance
issues.
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2. Move section switch printing to MCSection virtual method which takes a
TAI. This eliminates textual formatting stuff from TLOF.
3. Eliminate SwitchToSectionDirective, getSectionFlagsAsString, and
TLOFELF::AtIsCommentChar.
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A TAI hook is appropriate in this case because this is just an
asm syntax issue, not a semantic difference. TLOF should model
the semantics of the section.
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Blackfin supports and/or/xor on i32 but not on i16. Teach
DAGCombiner::SimplifyBinOpWithSameOpcodeHands to not produce illegal nodes
after legalize ops.
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Handle large integers, x86_fp80, ConstantAggregateZero, and two more ConstantExpr:
GetElementPtr and IntToPtr
Set SHF_MERGE bit for mergeable strings
Avoid zero initialized strings to be classified as a bss symbol
Don't allow common symbols to be classified as STB_WEAK
Add a constant to be used as a global value offset in data relocations
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Also don't dereference old pointers after they have been deleted causing
random crashes when enabling the machine code verifier.
Ahem...
I have not included a test case for the crash. It hapened when enabling the
verifier on CodeGen/X86/2009-08-06-branchfolder-crash.ll.
The crash depends on an MBB being allocated at the same address as a
previously deleted MBB. I don't think that can be reproduced reliably.
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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>
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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.
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- start support for new PEI w/reg alloc, allow running RS from emit{Pro,Epi}logue() target hooks.
- fix minor issue with recursion detection.
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and high-bits values in ways that weren't correct for integer
types wider than 64 bits. This fixes a miscompile in
PPMacroExpansion.cpp in clang on x86-64.
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a dirty hack and isn't need anymore since the last x86 code emitter patch)
- Add a target-dependent modifier to addend calculation
- Use R_X86_64_32S relocation for X86::reloc_absolute_word_sext
- Use getELFSectionFlags whenever possible
- fix getTextSection to use TLOF and emit the right text section
- Handle global emission for static ctors, dtors and Type::PointerTyID
- Some minor fixes
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Instead of awkwardly encoding calling-convention information with ISD::CALL,
ISD::FORMAL_ARGUMENTS, ISD::RET, and ISD::ARG_FLAGS nodes, TargetLowering
provides three virtual functions for targets to override:
LowerFormalArguments, LowerCall, and LowerRet, which replace the custom
lowering done on the special nodes. They provide the same information, but
in a more immediately usable format.
This also reworks much of the target-independent tail call logic. The
decision of whether or not to perform a tail call is now cleanly split
between target-independent portions, and the target dependent portion
in IsEligibleForTailCallOptimization.
This also synchronizes all in-tree targets, to help enable future
refactoring and feature work.
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Imp-def is *not* allowed to redefine a live register.
Imp-use is *not* allowed to use a dead register.
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the masm backend. If anyone cares about masm in the future,
we'll have semantic sections it can hang off of.
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For an undef operand, MO.getReg() is meaningless and we should not use it.
Undef operands should be skipped entirely.
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When LowerExtract eliminates an EXTRACT_SUBREG with a kill flag, it moves the
kill flag to the place where the sub-register is killed. This can accidentally
overlap with the use of a sibling sub-register, and we have trouble.
In the test case we have this code:
Live Ins: %R0 %R1 %R2
%R2L<def> = EXTRACT_SUBREG %R2<kill>, 1
%R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0]
%R1L<def> = EXTRACT_SUBREG %R1<kill>, 1
%R0L<def> = EXTRACT_SUBREG %R0<kill>, 1
%R0H<def> = ADD16 %R2H<kill>, %R2L<kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def>
subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1
subreg: eliminated!
subreg: killed here: %R0H<def> = ADD16 %R2H, %R2L, %R2<imp-use,kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def>
The kill flag on %R2 is moved to the last instruction, and the live range overlaps with the definition of %R2H:
*** Bad machine code: Redefining a live physical register ***
- function: f
- basic block: 0x18358c0 (#0)
- instruction: %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0]
Register R2H was defined but already live.
The fix is to replace EXTRACT_SUBREG with IMPLICIT_DEF instead of eliminating
it completely:
subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1
subreg: replace by: %R2L<def> = IMPLICIT_DEF %R2<kill>
Note that these IMPLICIT_DEF instructions survive to the asm output. It is
necessary to fix the stack-color-with-reg test case because of that.
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Implicit operands no longer get a free pass: Imp-use requires a live register
and imp-def requires a dead register.
There is also no special rule allowing redefinition of a sub-register when the
super-register is live. The super register must have imp-kill+imp-def operands
instead.
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killed by another operand.
There is probably a better fix. Either 1) scavenger can look at other operands, or
2) livevariables can be smarter about kill markers. Patches welcome.
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TLI.computeMaskedBitsForTargetNode from ComputeMaskedBits, since
the former may call back into the latter. This fixes a major
compile time problem on a testcase that happnened to hit this
in a particularly bad way, PR4643.
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When LowerSubregsInstructionPass::LowerInsert eliminates an INSERT_SUBREG
instriction because it is an identity copy, make sure that the same registers
are alive before and after the elimination.
When the super-register is marked <undef> this requires inserting an
IMPLICIT_DEF instruction to make sure the super register is live.
Fix a related bug where a kill flag on the inserted sub-register was not transferred properly.
Finally, clear the undef flag in MachineInstr::addRegisterKilled. Undef implies dead and kill implies live, so they cant both be valid.
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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.
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support. This isn't immediately interesting, because Legalize
ends up lowering SELECT_CC if the target doesn't support it,
but this simplifies the process.
Also, if the SELECT_CC would be expanded in Legalize, it
can potentially end up with two copies of the condition
expression. By leaving it as SELECT+SETCC, the SELECT can be
expanded into two SELECTs that use a single SETCC.
The two comparisons are usually CSE'd, but depending on
when various expressions get legalized, the comparison
expression could involve calls to library functions, such
that the comparison expression may not be able to be CSE'd.
This will be needed by a future patch.
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Use of an <undef> register is treated like an <imp-use>. It is not an error to use a dead <undef> register.
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behavior of the LSDA section instead of on some random target hook that
needs to be kept in synch with other points of truth.
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getLSDASection() to be more specific. This makes it pretty obvious
that the ELF LSDA section is being specified wrong in PIC mode. We're
probably getting a lot of startup-time relocations to a readonly page,
which is expensive and bad.
Someone who cares about ELF C++ should investigate this.
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compute it based on what it knows. As part of this, rename getSectionForMergeableConstant
to getSectionForConstant because it works for non-mergable constants also.
The only functionality change from this is that Xcore will start dropping
its jump tables into readonly section instead of data section in -static mode.
This should be fine as the linker resolves the relocations. If this is a
problem, let me know and we'll come up with another solution.
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to:
.quad X
even on a 32-bit system, where X is not 64-bits. There isn't much that
we can do here, so we just print:
.quad ((X) & 4294967295)
instead.
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should have no state that is specific to particular globals in the
section. In this case, it means the removal of the "isWeak" and
"ExplicitSection" bits. MCSection uses the new form of SectionKind.
To handle isWeak, I introduced a new SectionInfo class, which is
SectionKind + isWeak, and it is used by the part of the code generator
that does classification of a specific global.
The ExplicitSection disappears. It is moved onto MCSection as a new
"IsDirective" bit. Since the Name of a section is either a section
or directive, it makes sense to keep this bit in MCSection. Ultimately
the creator of MCSection should canonicalize (e.g.) .text to whatever
the actual section is.
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