[flang] Fix build on different of cores from #164630

[JDPailleux]

Normally fix incorrect linking introduced in #161179 with build in parallel.

[llvmbot]

@llvm/pr-subscribers-flang-fir-hlfir

Author: Jean-Didier PAILLEUX (JDPailleux)

Changes

Normally fix incorrect linking introduced in #161179 with build in parallel.

---

Full diff: https://github.com/llvm/llvm-project/pull/164841.diff

1 Files Affected:

• (modified) flang/lib/Optimizer/Dialect/MIF/CMakeLists.txt (-1)

diff --git a/flang/lib/Optimizer/Dialect/MIF/CMakeLists.txt b/flang/lib/Optimizer/Dialect/MIF/CMakeLists.txt
index ed8463e9b0330..d53937ebb49d4 100644
--- a/flang/lib/Optimizer/Dialect/MIF/CMakeLists.txt
+++ b/flang/lib/Optimizer/Dialect/MIF/CMakeLists.txt
@@ -8,7 +8,6 @@ add_flang_library(MIFDialect
   LINK_LIBS
   FIRDialect
   FIRDialectSupport
-  FIRSupport
 
   LINK_COMPONENTS
   AsmParser

[pawosm-arm]

This PR looks weird (removing things rather than adding to the CMakefile), but somehow it made our CI green. Note that I had to test for the other issue alongside, so it wasn't the recommended 'change one thing at a time' approach.

[tblah]

Thank you for taking time for looking into this but I don't think this is the whole right fix yet. The error message in #164630 would indicate a missing dependency between whatever is including MIFDialect.h and the CMake task which is generating the table gen parts of that header (MIFDialect).

I had a quick look and I see that the header file is included from flang/include/flang/Optimizer/Support/InitFIR.h. FIRSupport has no dependency upon MIFDialect and so there is no guarantee that it will be built after MIFDialect.

I think removing the dependency from MIFDialect to FIRSupport makes the issue much less likely (because CMake won't be trying to build FIRSupport before it has built MIFDialect) but it doesn't guarantee that the build order will be correct in the future for all machines.

Beware that the dependency is created by the presence of the include in a header (InitFIR.h) and so every library that includes InitFIR.h will also depend upon MIFDialect. However, they should already have a dependency on FIRSupport so it should come through transitively once FIRSupport has the right dependency.

I hope that made sense. Please feel free to ask me questions here or on the flang slack if I can help at all :)

[JDPailleux]

That was my conclusion. I was unable to reproduce the dependency issue on my side.
My only indication was the FIRSupport dependency in MIFDialect, and the MIFDialect header in "InitFIR.h" could produce the dependency error.
So, as @tblah mentions, removing the dependency from MIFDialect to FIRSupport makes the issue much less likely.

[pawosm-arm]

So, as @tblah mentions, removing the dependency from MIFDialect to FIRSupport makes the issue much less likely.

Seems like flang suffers from a major design issue when it comes to specifying dependencies.