This reduces the size of a statically linked Phobos-based
Hello World by 11 kB on Linux x86_64.
Also creates a header file for gen/module.cpp, which has been
renamed to "modules" such as not to conflict with the frontend
header file.
Modern Linux distributions have their toolchain generate PIC code for
additional security features (like ASLR).
Since there is no (sane) way to detect whether the toolchain defaults to
PIC code, we simply default to PIC code on all Linux
distributions to avoid linking issues on these OSes.
The relocation model can be switched back to non-PIC code manually at
any time.
LLVM's ParseCommandLineOptions() expands response files automatically, but
always uses the TokenizeGNUCommandLine tokenizer, which apparently eats
backslashes.
The solution is to pre-expand the response files into the arguments vector
on the LDC side, and using TokenizeWindowsCommandLine if LDC is built for
Windows.
We had switched to a somewhat simplified implementation Martin
came up with for DMD based on our old one. Unfortunately, that
turned out not to work for certain ld.bfd versions on Linux
(e.g. 2.26.0.20160501), where the .bss section from other shared
objects would be picked up instead.
This reverts commit 08ad4fddb5.
GitHub: Fixes#1534.
Add the commandline options -fprofile-instr-generate[=filename] and -profile-instr-use=filename
-fprofile-instr-generate
-- Add instrumentation on branches, switches, and function entry; uses LLVM's InstrProf pass.
-- Link to profile runtime that writes instrumentation counters to a file.
-fprofile-instr-use
-- Read profile data from a file and apply branch weights to branches and switches, and annotate functions with entrycount in LLVM IR.
-- Functions with low or high entrycount are marked with 'cold' or 'inlinehint'.
The only statement type without PGO yet is "try-finally".
A new pragma, `pragma(LDC_profile_instr, [ true | false ])`, is added to selectively disable/enable instrumentation of functions (granularity = whole functions).
The runtime library ldc-profile-rt is a copy of LLVM compiler-rt lib/profile. It has to be exactly in-sync with the LLVM version, and thus we need a copy for each PGO-supported LLVM (>=3.7).
import ldc.profile for a D interface to ldc-profile-rt (for example to reset execution counts after a program startup phase).
The instrumentation data is mainly passed on to LLVM: function-entry counts and branch counts/probabilities. LDC marks functions as hot when "execution count is 30% of the maximum function execution count", and marks functions as cold if their count is 1% of maximum function execution count.
The source of LLVM's llvm-profdata tool is hereby included in LDCs repository (different source for each LLVM version), and the binary is included in the install bin folder.
The executable is named "ldc-profdata" to avoid clashing with llvm-profdata on the same machine. This is needed because profdata executable has to be in-sync with the LLVM version used to build LDC.
Maintenance burden: for trunk LLVM, we have to keep ldc-profile-rt and llvm-profdata in sync. There is no diff with upstream; but because of active development there are the occasional API changes.
The temporary files created should be unique for parallel processes (e.g. in a test suite where LDC is called in parallel with perhaps same input).
These files will be deleted after execution so their name is not relevant. For better linking errors, the new filenames are created by appending random characters to their name.
