Improve Chapel LLVM support

[mppf]

Update Chapel to work with master LLVM and improve script for working with LLVM master

• fixes minor API changes from LLVM 7
• enables update-llvm script to take an argument specifying branch to use
• update-llvm also checks out Polly to support current development efforts
• prototype RV integration included but off by default. It is not ready for prime-time but I didn't want to lose track of the small number of changes.

For example, here is the way to use update-llvm.sh to checkout master version of llvm/clang/...:

# to enable LLVM debug information (not required but might be helpful)
export CHPL_LLVM_DEVELOPER=1
# to enable building LLVM with Chapel compiler
export CHPL_LLVM=llvm

# Clear out previous llvm directory / build
make clobber

# check out the branch of LLVM you want to use
# e.g. release_601
# (if no branch is specified, the script will use a branch name
#  computed from LLVM_VERSION
#  which is the version bundled with Chapel)
# Note, running update-llvm again without clobbering
# will 'git pull --rebase'
cd third-party/llvm
./update-llvm.sh master
cd ../..

# build LLVM and Chapel compiler using it
make

# add built LLVM tools to your path
export PATH=`pwd`/third-party/llvm/install/linux64-gnu/bin/:$PATH

• full local --llvm testing

Reviewed by @dmk42 - thanks!

[mppf]

@ysahil97 - this works for me like this (starting from the instructions above to build Chapel with LLVM master, and starting from this branch for Chapel):

in s.chpl (this is just your affine_initialization.chpl example):

config const n = 10;
proc test(){
 var A:[1..n] real;
 for i in 1..n{
  A(i) = i;
 }
}
test();

chpl s.chpl --llvm --llvm-print-ir=test --llvm-print-ir-stage=full > s.ll
opt -O3 -polly -analyze -pass-remarks-missed=polly-detect -pass-remarks=polly-detect -pass-remarks-analysis=polly-detect s.ll

Polly outputs:

remark: <unknown>:0:0: The following errors keep this region from being a Scop.
remark: <unknown>:0:0: No profitable polyhedral optimization found
remark: <unknown>:0:0: Invalid Scop candidate ends here.
remark: <unknown>:0:0: The following errors keep this region from being a Scop.
remark: <unknown>:0:0: Failed to derive an affine function from the loop bounds.
remark: <unknown>:0:0: Invalid Scop candidate ends here.
remark: <unknown>:0:0: The following errors keep this region from being a Scop.
remark: <unknown>:0:0: This function call cannot be handled. Try to inline it.
remark: <unknown>:0:0: Invalid Scop candidate ends here.

[ysahil97]

Thanks @mppf for this.
The polly output seems to be fine. We can improve on this by appending -g flag after chpl. This helps us in getting the debug info for each and every remark obtained.

[mppf]

Sure, and that seems to give line numbers for me. But it doesn't say what function was called etc.

[mppf]

I tried it with --fast too:

$ chpl s.chpl --fast -g --llvm --llvm-print-ir=test --llvm-print-ir-stage=full > s.ll
$ opt -O3 -polly -analyze -pass-remarks-missed=polly-detect -pass-remarks=polly-detect -pass-remarks-analysis=polly-detect s.ll
...
remark: s.chpl:4:0: The following errors keep this region from being a Scop.
remark: s.chpl:4:0: No profitable polyhedral optimization found
remark: s.chpl:5:0: Invalid Scop candidate ends here.
...

[dmk42]

Very cool. Looks good.