https://github.com/llvm/llvm-project/pull/178333 updates the memprof
pass to annotate string literal section prefix.
The StaticDataProfileInfo.cpp provides an analysis pass to reconcile
global variable hotness. It's used by StaticDataAnnotator and AsmPrinter
to look up global variable hotness.
This PR updates the analysis pass to compute the hotness of string
literals.
* When both data access profiles and pgo counters provide a hotness
attribute, use the hotter one.
* Otherwise, use the hotness attribute that's available.
Implementation-wise, the option `AnnotateStringLiteralSectionPrefix` is
moved from MemProf (a transform pass) to StaticDataProfileInfo (an
Analysis pass). Otherwise, there might be errors like caught by CI. Note
https://github.com/llvm/llvm-project/pull/178336#issuecomment-3808537817
is an edited message, and its history shows the intermediate failures
like below. ~My understanding is~ Preliminary LLM study (:)) shows that
the error manifests in PowerPC but not X86 due to cmake variable
differences.
```
FAILED: unittests/Target/PowerPC/PowerPCTests
...
>>> referenced by CommandLine.h:1437 (/home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/include/llvm/Support/CommandLine.h:1437)
>>> StaticDataProfileInfo.cpp.o:(llvm::StaticDataProfileInfo::getConstantSectionPrefix(llvm::Constant const*, llvm::ProfileSummaryInfo const*) const) in archive lib/libLLVMAnalysis.a
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
```
This PR enhances the `StaticDataProfileInfo::getConstantSectionPrefix`
pass to reconcile data hotness information from both PGO counters and
data access profiles. When both profiles are available for a global
variable, the pass will now use the "hotter" of the two to determine the
variable's section placement.
This is a follow-up patch of
https://github.com/llvm/llvm-project/pull/162388
This change introduces new helper functions to check if a global
variable is eligible for section prefix annotation.
This shared logic is used by both MemProfUse and StaticDataSplitter to
avoid annotating ineligible variables.
This is the 2nd patch as a split of
https://github.com/llvm/llvm-project/pull/155337
These are identified by misc-include-cleaner. I've filtered out those
that break builds. Also, I'm staying away from llvm-config.h,
config.h, and Compiler.h, which likely cause platform- or
compiler-specific build failures.
In this PR, static-data-splitter pass finds out the local-linkage global
variables in {`.rodata`, `.data.rel.ro`, `bss`, `.data`} sections by
analyzing machine instruction operands, and aggregates their accesses
from code across functions.
A follow-up item is to analyze global variable initializers and count
for access from data.
* This limitation is demonstrated by `bss2` and `data3` in
`llvm/test/CodeGen/X86/global-variable-partition.ll`.
Some stats of static-data-splitter with this patch:
**section**|**bss**|**rodata**|**data**
:-----:|:-----:|:-----:|:-----:
hot-prefixed section coverage|99.75%|97.71%|91.30%
unlikely-prefixed section size percentage|67.94%|39.37%|63.10%
1. The coverage is defined as `#perf-sample-in-hot-prefixed <data>
section / #perf-sample in <data.*> section` for each <data> section.
* The perf command samples
`MEM_INST_RETIRED.ALL_LOADS:u:pinned:precise=2` events at a high
frequency (`perf -c 2251`) for 30 seconds. The profiled binary is built
as non-PIE so `data.rel.ro` coverage data is not available.
2. The unlikely-prefixed `<data>` section size percentage is defined as
`unlikely <data> section size / the sum size of <data>.* sections` for
each `<data>` section
