This patch is a large number of small changes that should hopefully not
affect the generated machine code but are still important to get right
so that the machine verifier won't complain about them.
The llvm/test/CodeGen/AVR/pseudo/*.mir changes are also necessary
because without the liveins the used registers are considered undefined
by the machine verifier and it will complain about them.
Differential Revision: https://reviews.llvm.org/D97172
The previous expansion used SBCI, which is incorrect because the NEGW
pseudo instruction accepts a DREGS operand (2xGPR8) and SBCI only allows
LD8 registers. One solution could be to correct the NEGW pseudo
instruction, but another solution is to use a different instruction
(sbc) that does accept a GPR8 register and therefore allows more freedom
to the register allocator.
The output now matches avr-gcc for the following code:
int foo(int n) {
return -n;
}
I've found this issue using the machine instruction verifier: it was
complaining about the wrong register class in NEGWRd.mir.
Differential Revision: https://reviews.llvm.org/D97131
Summary:
LDRdPtr expanded from LDWRdPtr shouldn't define its second operand(SrcReg).
The second operand is its source register.
Add -verify-machineinstrs into command line of testcases can trigger this error.
Reviewers: dylanmckay
Reviewed By: dylanmckay
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D75437
Summary:
LDWRdPtr would be expanded to ld+ldd. ldd only accepts the pointer register is Y or Z.
So the register class of pointer of LDWRdPtr should be PTRDISPREGS instead of PTRREGS.
Reviewers: dylanmckay
Reviewed By: dylanmckay
Subscribers: dylanmckay, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D62300
llvm-svn: 362351
Prior to this patch, the AVR::LDWRdPtr instruction was always lowered to
instructions of this pattern:
ld $GPR8, [PTR:XYZ]+
ld $GPR8, [PTR]+1
This has a problem; the [PTR] is incremented in-place once, but never
decremented.
Future uses of the same pointer will use the now clobbered value,
leading to the pointer being incorrect by an offset of one.
This patch modifies the expansion code of the LDWRdPtr pseudo
instruction so that the pointer variable is not silently clobbered in
future uses in the same live range.
Bug first reported by Keshav Kini.
Patch by Kaushik Phatak.
llvm-svn: 351673
This reverts commit r351544.
In that commit, I had mistakenly misattributed the issue submitter as
the patch author, Kaushik Phatak.
The patch will be recommitted immediately with the correct attribution.
llvm-svn: 351672
Prior to this patch, the AVR::LDWRdPtr instruction was always lowered to
instructions of this pattern:
ld $GPR8, [PTR:XYZ]+
ld $GPR8, [PTR]+1
This has a problem; the [PTR] is incremented in-place once, but never
decremented.
Future uses of the same pointer will use the now clobbered value,
leading to the pointer being incorrect by an offset of one.
This patch modifies the expansion code of the LDWRdPtr pseudo
instruction so that the pointer variable is not silently clobbered in
future uses in the same live range.
Patch by Keshav Kini.
llvm-svn: 351544
This is an AVR-specific workaround for a limitation of the register
allocator that only exposes itself on targets with high register
contention like AVR, which only has three pointer registers.
The three pointer registers are X, Y, and Z.
In most nontrivial functions, Y is reserved for the frame pointer,
as per the calling convention. This leaves X and Z. Some instructions,
such as LPM ("load program memory"), are only defined for the Z
register. Sometimes this just leaves X.
When the backend generates a LDDWRdPtrQ instruction with Z as the
destination pointer, it usually trips up the register allocator
with this error message:
LLVM ERROR: ran out of registers during register allocation
This patch is a hacky workaround. We ban the LDDWRdPtrQ instruction
from ever using the Z register as an operand. This gives the
register allocator a bit more space to allocate, fixing the
regalloc exhaustion error.
Here is a description from the patch author Peter Nimmervoll
As far as I understand the problem occurs when LDDWRdPtrQ uses
the ptrdispregs register class as target register. This should work, but
the allocator can't deal with this for some reason. So from my testing,
it seams like (and I might be totally wrong on this) the allocator reserves
the Z register for the ICALL instruction and then the register class
ptrdispregs only has 1 register left and we can't use Y for source and
destination. Removing the Z register from DREGS fixes the problem but
removing Y register does not.
More information about the bug can be found on the avr-rust issue
tracker at https://github.com/avr-rust/rust/issues/37.
A bug has raised to track the removal of this workaround and a proper
fix; PR39553 at https://bugs.llvm.org/show_bug.cgi?id=39553.
Patch by Peter Nimmervoll
llvm-svn: 346114
The 'rol Rd' instruction is equivalent to 'adc Rd'.
This caused compile warnings from tablegen because of conflicting bits
shared between each instruction.
llvm-svn: 341275
Summary: This gets rid of the hardcoded 'r0' that was used previously.
Reviewers: asl
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D27567
llvm-svn: 289322
Ayke van Laethem