From ed4328c607306a2aa6df4833a0dce4482edbc94c Mon Sep 17 00:00:00 2001
From: Simon Tatham <simon.tatham@arm.com>
Date: Tue, 30 Jun 2020 08:51:51 +0100
Subject: [PATCH] Fix missing build dependency on omp_gen.

Summary:
`include/llvm/Frontend/OpenMP/CMakeLists.txt` creates a new target
called `omp_gen`, which is automatically added to
`LLVM_COMMON_DEPENDS` by the `add_public_tablegen_target` macro. But
it only gets added to the version of `LLVM_COMMON_DEPENDS` in the
scope of that subsidiary CMakeLists file, and it doesn't propagate all
the way back up to the permanent version of that variable which is
actually used to set dependencies.

The visible effect is that the output build scripts contain a missing
dependency. For example, if I run cmake in Ninja output mode, and then
run

  ninja -t commands tools/clang/examples/PrintFunctionNames/CMakeFiles/PrintFunctionNames.dir/PrintFunctionNames.cpp.o

to list all the commands that are prerequisites of building that
object file, then the list does not include the llvm-tblgen command
that builds `include/llvm/Frontend/OpenMP/OMP.h.inc`, even though that
generated include file is needed (by a chain of includes starting from
`clang/AST/AST.h`), and that object file can't be compiled without it.
This missing dependency can cause intermittent build failures,
depending on the order that Ninja (or whatever) happens to schedule
its commands.

I've fixed it by adding a `set` command in two levels of
`CMakeLists.txt` to propagate the modified version of
`LLVM_COMMON_DEPENDS` back up through the parent scopes so that
`omp_gen` does end up on the version seen by the main
`llvm/CMakeLists.txt`.

Reviewers: clementval, thakis, chandlerc, jdoerfert

Reviewed By: clementval

Subscribers: jdenny, mgorny, sstefan1, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D82659
---
 llvm/include/llvm/CMakeLists.txt                 | 2 ++
 llvm/include/llvm/Frontend/OpenMP/CMakeLists.txt | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/llvm/include/llvm/CMakeLists.txt b/llvm/include/llvm/CMakeLists.txt
index 7cf8699a..29c1c74 100644
--- a/llvm/include/llvm/CMakeLists.txt
+++ b/llvm/include/llvm/CMakeLists.txt
@@ -7,3 +7,5 @@ add_subdirectory(Frontend/OpenMP)
 if (NOT "${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_BINARY_DIR}")
   configure_file(module.modulemap.build module.modulemap COPYONLY)
 endif (NOT "${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_BINARY_DIR}")
+
+set(LLVM_COMMON_DEPENDS ${LLVM_COMMON_DEPENDS} PARENT_SCOPE)
diff --git a/llvm/include/llvm/Frontend/OpenMP/CMakeLists.txt b/llvm/include/llvm/Frontend/OpenMP/CMakeLists.txt
index 9bdc4b8..5215070 100644
--- a/llvm/include/llvm/Frontend/OpenMP/CMakeLists.txt
+++ b/llvm/include/llvm/Frontend/OpenMP/CMakeLists.txt
@@ -1,3 +1,5 @@
 set(LLVM_TARGET_DEFINITIONS OMP.td)
 tablegen(LLVM OMP.h.inc --gen-directive-decls)
 add_public_tablegen_target(omp_gen)
+
+set(LLVM_COMMON_DEPENDS ${LLVM_COMMON_DEPENDS} PARENT_SCOPE)
-- 
2.7.4