For IR generated by a compiler, this is really simple: you just take the
datalayout from the beginning of the file, and apply it to all the IR
later in the file. For optimization testcases that don't care about the
datalayout, this is also really simple: we just use the default
datalayout.
The complexity here comes from the fact that some LLVM tools allow
overriding the datalayout: some tools have an explicit flag for this,
some tools will infer a datalayout based on the code generation target.
Supporting this properly required plumbing through a bunch of new
machinery: we want to allow overriding the datalayout after the
datalayout is parsed from the file, but before we use any information
from it. Therefore, IR/bitcode parsing now has a callback to allow tools
to compute the datalayout at the appropriate time.
Not sure if I covered all the LLVM tools that want to use the callback.
(clang? lli? Misc IR manipulation tools like llvm-link?). But this is at
least enough for all the LLVM regression tests, and IR without a
datalayout is not something frontends should generate.
This change had some sort of weird effects for certain CodeGen
regression tests: if the datalayout is overridden with a datalayout with
a different program or stack address space, we now parse IR based on the
overridden datalayout, instead of the one written in the file (or the
default one, if none is specified). This broke a few AVR tests, and one
AMDGPU test.
Outside the CodeGen tests I mentioned, the test changes are all just
fixing CHECK lines and moving around datalayout lines in weird places.
Differential Revision: https://reviews.llvm.org/D78403
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
Eli Friedman