Most of the PowerPC64 code generation for the ELF ABI is already PIC.
There are four main exceptions:
(1) Constant pointer arrays etc. should in writeable sections.
(2) The TOC restoration NOP after a call is needed for all global
symbols. While GNU ld has a workaround for questionable GCC self-calls,
we trigger the checks for calls from COMDAT sections as they cross input
sections and are therefore not considered self-calls. The current
decision is questionable and suboptimal, but outside the scope of the
change.
(3) TLS access can not use the initial-exec model.
(4) Jump tables should use relative addresses. Note that the current
encoding doesn't work for the large code model, but it is more compact
than the default for any non-trivial jump table. Improving this is again
beyond the scope of this change.
At least (1) and (3) are assumptions made in target-independent code and
introducing additional hooks is a bit messy. Testing with clang shows
that a -fPIC binary is 600KB smaller than the corresponding -fno-pic
build. Separate testing from improved jump table encodings would explain
only about 100KB or so. The rest is expected to be a result of more
aggressive immediate forming for -fno-pic, where the -fPIC binary just
uses TOC entries.
This change brings the LLVM output in line with the GCC output, other
PPC64 compilers like XLC on AIX are known to produce PIC by default
as well. The relocation model can still be provided explicitly, i.e.
when using MCJIT.
One test case for case (1) is included, other test cases with relocation
mode sensitive behavior are wired to static for now. They will be
reviewed and adjusted separately.
Differential Revision: https://reviews.llvm.org/D26566
llvm-svn: 289743
When we have an offset into a global, etc. that is accessed relative to the TOC
base pointer, and the offset is larger than the minimum alignment of the global
itself and the TOC base pointer (which is 8-byte aligned), we can still fold
the @toc@ha into the memory access, but we must update the addis instruction's
symbol reference with the offset as the symbol addend. When there is only one
use of the addi to be folded and only one use of the addis that would need its
symbol's offset adjusted, then we can make the adjustment and fold the @toc@l
into the memory access.
llvm-svn: 280545
When applying our address-formation PPC64 peephole, we are reusing the @ha TOC
addis value with the low parts associated with different offsets (i.e.
different effective symbol addends). We were assuming this was okay so long as
the offsets were less than the alignment of the global variable being accessed.
This ignored the fact, however, that the TOC base pointer itself need only be
8-byte aligned. As a result, what we were doing is legal only for offsets less
than 8 regardless of the alignment of the object being accessed.
Fixes PR28727.
llvm-svn: 280441
The logic in this function assumes that the P8 supports fusion of addis/addi,
but it does not. As a result, there is no advantage to restricting our peephole
application, merging addi instructions into dependent memory accesses, even
when the addi has multiple users, regardless of whether or not we're optimizing
for size.
We might need something like this again for the P9; I suspect we'll revisit
this code when we work on P9 tuning.
llvm-svn: 280440
Currently we have a number of tests that fail with -verify-machineinstrs.
To detect this cases earlier we add the option to the testcases with the
exception of tests that will currently fail with this option. PR 27456 keeps
track of this failures.
No code review, as discussed with Hal Finkel.
llvm-svn: 277624
Access to aligned globals gives us a chance to peephole optimize nonzero
offsets. If a struct is 4 byte aligned, then accesses to bytes 0-3 won't
overflow the available displacement. For example:
addis 3, 2, b4v@toc@ha
addi 4, 3, b4v@toc@l
lbz 5, b4v@toc@l(3) ; This is the result of the current peephole
lbz 6, 1(4) ; optimizer
lbz 7, 2(4)
lbz 8, 3(4)
If b4v is 4-byte aligned, we can skip using register 4 because we know
that b4v@toc@l+{1,2,3} won't overflow 32K, and instead generate:
addis 3, 2, b4v@toc@ha
lbz 4, b4v@toc@l(3)
lbz 5, b4v@toc@l+1(3)
lbz 6, b4v@toc@l+2(3)
lbz 7, b4v@toc@l+3(3)
Saving a register and an addition.
Larger alignments allow larger structures/arrays to be optimized.
llvm-svn: 255319
Joerg Sonnenberger