llvm-exegesis build on x86 doesn't set LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET

[tycho]

Bugzilla Link	39021
Resolution	FIXED
Resolved on	Nov 28, 2018 13:46
Version	7.0
OS	Linux
Blocks	#38454
CC	@legrosbuffle,@gchatelet,@zmodem,@RKSimon,@tstellar
Fixed by commit(s)	r342865 r347811

Extended Description

Something's up with the llvm-exegesis build process on 7.0.0 release. On my x86 machines they always complain "no exegesis target for x86_64-pc-linux-gnu, using default", and this seems to be because LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET never gets set by CMake.

The CMake scripts try to set LLVM_EXEGESIS_TARGETS in the lib subdirectory, but this doesn't seem to work properly. I made this change to figure out what's happening:

---

diff --git a/tools/llvm-exegesis/CMakeLists.txt b/tools/llvm-exegesis/CMakeLists.txt
index 65b1ada8529..94842519ca7 100644
--- a/tools/llvm-exegesis/CMakeLists.txt
+++ b/tools/llvm-exegesis/CMakeLists.txt
@@ -8,7 +8,9 @@ add_llvm_tool(llvm-exegesis
llvm-exegesis.cpp
)

+message(WARNING "LLVM_EXEGESIS_TARGETS at parent scope before: ${LLVM_EXEGESIS_TARGETS}")
add_subdirectory(lib)
+message(FATAL_ERROR "LLVM_EXEGESIS_TARGETS at parent scope after: ${LLVM_EXEGESIS_TARGETS}")

Link the native exegesis target if compiled and on the right host.

if ((LLVM_TARGETS_TO_BUILD MATCHES "${LLVM_NATIVE_ARCH}") AND (LLVM_EXEGESIS_TARGETS MATCHES "${LLVM_NATIVE_ARCH}"))
diff --git a/tools/llvm-exegesis/lib/CMakeLists.txt b/tools/llvm-exegesis/lib/CMakeLists.txt
index 175c2adf9de..4dc91ef125c 100644
--- a/tools/llvm-exegesis/lib/CMakeLists.txt
+++ b/tools/llvm-exegesis/lib/CMakeLists.txt
@@ -1,12 +1,18 @@
+message( WARNING "LLVM_EXEGESIS_TARGETS before: ${LLVM_EXEGESIS_TARGETS}" )
+
if (LLVM_TARGETS_TO_BUILD MATCHES "X86")
add_subdirectory(X86)

• message( WARNING "Appending X86" )
  set(LLVM_EXEGESIS_TARGETS "${LLVM_EXEGESIS_TARGETS} X86" PARENT_SCOPE)
  endif()
  if (LLVM_TARGETS_TO_BUILD MATCHES "AArch64")
  add_subdirectory(AArch64)
• message( WARNING "Appending AArch64" )
  set(LLVM_EXEGESIS_TARGETS "${LLVM_EXEGESIS_TARGETS} AArch64" PARENT_SCOPE)
  endif()

+message( WARNING "LLVM_EXEGESIS_TARGETS after: ${LLVM_EXEGESIS_TARGETS}" )
+
add_library(LLVMExegesis
STATIC
Analysis.cpp

---

This results in this behavior (extraneous newlines removed for readability):

CMake Warning at tools/llvm-exegesis/CMakeLists.txt:11 (message):
LLVM_EXEGESIS_TARGETS at parent scope before:
CMake Warning at tools/llvm-exegesis/lib/CMakeLists.txt:1 (message):
LLVM_EXEGESIS_TARGETS before:
CMake Warning at tools/llvm-exegesis/lib/CMakeLists.txt:5 (message):
Appending X86
CMake Warning at tools/llvm-exegesis/lib/CMakeLists.txt:10 (message):
Appending AArch64
CMake Warning at tools/llvm-exegesis/lib/CMakeLists.txt:14 (message):
LLVM_EXEGESIS_TARGETS after:
CMake Error at tools/llvm-exegesis/CMakeLists.txt:13 (message):
LLVM_EXEGESIS_TARGETS at parent scope after: AArch64

So reading the LLVM_EXEGESIS_TARGETS variable in lib/CMakeLists.txt doesn't work properly, and the second set(... PARENT_SCOPE) just sees the empty LLVM_EXEGESIS_TARGETS value, overwriting the previously appended X86 value.

Any ideas on how to fix this? I'm doing this locally but it seems sloppy:

diff --git a/tools/llvm-exegesis/lib/CMakeLists.txt b/tools/llvm-exegesis/lib/CMakeLists.txt
index 175c2adf9de..194304adf98 100644
--- a/tools/llvm-exegesis/lib/CMakeLists.txt
+++ b/tools/llvm-exegesis/lib/CMakeLists.txt
@@ -1,12 +1,16 @@
+set(TARGETS_TO_APPEND "")
+
if (LLVM_TARGETS_TO_BUILD MATCHES "X86")
add_subdirectory(X86)

• set(LLVM_EXEGESIS_TARGETS "${LLVM_EXEGESIS_TARGETS} X86" PARENT_SCOPE)

• set(TARGETS_TO_APPEND "${TARGETS_TO_APPEND} X86")
  endif()
  if (LLVM_TARGETS_TO_BUILD MATCHES "AArch64")
  add_subdirectory(AArch64)

• set(LLVM_EXEGESIS_TARGETS "${LLVM_EXEGESIS_TARGETS} AArch64" PARENT_SCOPE)

• set(TARGETS_TO_APPEND "${TARGETS_TO_APPEND} AArch64")
  endif()

+set(LLVM_EXEGESIS_TARGETS "${LLVM_EXEGESIS_TARGETS} ${TARGETS_TO_APPEND}" PARENT_SCOPE)
+
add_library(LLVMExegesis
STATIC
Analysis.cpp

[tycho]

assigned to @legrosbuffle

[legrosbuffle]

Thanks for the analysis

When https://reviews.llvm.org/D48778 introduced the PARENT_SCOPE there was only one target, so this was invisible. This started happening when a second target was added and only when building for both X86 and AArch64 targets.

I think your solution is reasonable, I've created //reviews.llvm.org/D52343. Thanks !

[RKSimon]

Hans - this probably needs to be fixed in the 7.0 dot release

[legrosbuffle]

Fixed by D52343/r342865.

[zmodem]

Hans - this probably needs to be fixed in the 7.0 dot release

Noted, thanks!

[RKSimon]

Reopened until merged for 7.0.1

[tstellar]

Clement, is this OK to merge to the release_70 branch?

[legrosbuffle]

Sorry, I've already replied by email: Yes, this can be merged.

[tstellar]

Merged: r347811

[tstellar]

mentioned in issue #38454