With cb57b7a7, the kill flags are now tracked during the forward search over
the instructions and the call to findRegisterUseOperandIdx() should therefore
only check for killing uses.
As shown with the failing test CodeGen/Hexagon/vector-sint-to-fp.ll, it could
otherwise be the case that an undef use after the instruction that killed the
register will be inserted into MBBKills, and the kill flag will not be
cleared.
It was discovered that this pass could be slow on huge functions, meaning 20%
compile time instead of the usual ~0.5% (with a test case spending ~19 mins
just in the backend).
The problem related to the necessary clearing of earlier kill flags when a
redundant instruction is removed. With this patch, the handling of kill flags
is now done by maintaining a map instead of scanning backwards in the
function. This remedies the compile time on the huge file fully.
Reviewed By: vpykhtin, arsenm
Differential Revision: https://reviews.llvm.org/D147532
Resolves https://github.com/llvm/llvm-project/issues/61397
If the removable definition resides in an INLINEASM_BR target, the
reuseable candidate might not dominate the INLINEASM_BR.
bb0:
INLINEASM_BR &"" %bb.1
renamable $x8 = MOVi64imm 29273397577910035
B %bb.2
...
bb1:
renamable $x8 = MOVi64imm 29273397577910035
renamable $x8 = ADDXri killed renamable $x8, 2048, 0
bb2:
Removing the second mov is a hazard when the inline asm branches to bb1.
Skip such replacements when the to be removed instruction is in the
target of such an INLINEASM_BR instruction.
We could get more aggressive about this in the future, but for now
simply abort.
This is causing a boot failure on linux-4.19.y branches of the LTS Linux
kernel for ARCH=arm64 with CONFIG_RANDOMIZE_BASE=y (KASLR) and
CONFIG_UNMAP_KERNEL_AT_EL0=y (KPTI).
Link: https://reviews.llvm.org/D123394
Link: https://github.com/ClangBuiltLinux/linux/issues/1837
Thanks to @nathanchance for the report, and @ardb for debugging.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D149191
This reverts commit 122efef8ee9be57055d204d52c38700fe933c033.
- Patch fixed to not reuse definitions from predecessors in EH landing pads.
- Late review suggestions (by MaskRay) have been addressed.
- M68k/pipeline.ll test updated.
- Init captures added in processBlock() to avoid capturing structured bindings.
- RISCV has this disabled for now.
Original commit message:
A new pass MachineLateInstrsCleanup is added to be run after PEI.
This is a simple pass that removes redundant and identical instructions
whenever found by scanning the MF once while keeping track of register
definitions in a map. These instructions are typically immediate loads
resulting from rematerialization, and address loads emitted by target in
eliminateFrameInde().
This is enabled by default, but a target could easily disable it by means of
'disablePass(&MachineLateInstrsCleanupID);'.
This late cleanup is naturally not "optimal" in removing instructions as it
is done by looking at phys-regs, but still quite effective. It would be
desirable to improve other parts of CodeGen and avoid these redundant
instructions in the first place, but there are no ideas for this yet.
Differential Revision: https://reviews.llvm.org/D123394
Reviewed By: RKSimon, foad, craig.topper, arsenm, asb
Init captures added in processBlock() to avoid capturing structured bindings,
which caused the build problems (with clang).
RISCV has this disabled for now until problems relating to post RA pseudo
expansions are resolved.
A new pass MachineLateInstrsCleanup is added to be run after PEI.
This is a simple pass that removes redundant and identical instructions
whenever found by scanning the MF once while keeping track of register
definitions in a map. These instructions are typically immediate loads
resulting from rematerialization, and address loads emitted by target in
eliminateFrameInde().
This is enabled by default, but a target could easily disable it by means of
'disablePass(&MachineLateInstrsCleanupID);'.
This late cleanup is naturally not "optimal" in removing instructions as it
is done by looking at phys-regs, but still quite effective. It would be
desirable to improve other parts of CodeGen and avoid these redundant
instructions in the first place, but there are no ideas for this yet.
Differential Revision: https://reviews.llvm.org/D123394
Reviewed By: RKSimon, foad, craig.topper, arsenm, asb
