[llvm] [llvm-(min-)tblgen] Avoid redundant source compilation (PR #114494)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-tablegen

Author: Michael Kruse (Meinersbur)

<details>
<summary>Changes</summary>

All the sources of `llvm-min-tblgen` are also used for `llvm-tblgen`, with identical compilation flags. Reuse the object files of `llvm-min-tblgen` for `llvm-tblgen`.

While this slightly reduces build time, the main motivation is ccache. Using the [hard_link](https://ccache.dev/manual/latest.html#config_hard_link) option, building the object files for `llvm-tblgen` will result in a hard link to the same object file already used for `llvm-min-tblgen`. To signal the build system that the file is new, ccache  will update the file's time stamp. Unfortunately, time stamps a shared between all hard-linked file s.t. this will also update the time stamps for the object files used for `llvm-min-tblgen`. At the next run, Ninja will recognize this time stamp discrepancy to the expected stamp recorded in `.ninja_log` and rebuild those object files for `llvm-min-tblgen`, which again will also update the stamp for the `llvm-min-tblgen`... . This is especially annoying for `llvm-(min)-tablegen` because it means Ninja will rerun all tablegenning in every build.

I am using the hard_link option because it reduces the cost of having multiple build-trees of the same LLVM source tree and reduces the wear to the SSD they are stored on.

---
Full diff: https://github.com/llvm/llvm-project/pull/114494.diff


1 Files Affected:

- (modified) llvm/utils/TableGen/CMakeLists.txt (+2-7) 


``````````diff
diff --git a/llvm/utils/TableGen/CMakeLists.txt b/llvm/utils/TableGen/CMakeLists.txt
index ba1e4aa01b48d6..ded2e228dcd6de 100644
--- a/llvm/utils/TableGen/CMakeLists.txt
+++ b/llvm/utils/TableGen/CMakeLists.txt
@@ -32,10 +32,8 @@ set(LLVM_LINK_COMPONENTS
 add_tablegen(llvm-tblgen LLVM
   DESTINATION "${LLVM_TOOLS_INSTALL_DIR}"
   EXPORT LLVM
-  ARMTargetDefEmitter.cpp
   AsmMatcherEmitter.cpp
   AsmWriterEmitter.cpp
-  Attributes.cpp
   CallingConvEmitter.cpp
   CodeEmitterGen.cpp
   CodeGenMapTable.cpp
@@ -48,7 +46,6 @@ add_tablegen(llvm-tblgen LLVM
   DecoderEmitter.cpp
   DFAEmitter.cpp
   DFAPacketizerEmitter.cpp
-  DirectiveEmitter.cpp
   DisassemblerEmitter.cpp
   DXILEmitter.cpp
   ExegesisEmitter.cpp
@@ -57,18 +54,14 @@ add_tablegen(llvm-tblgen LLVM
   GlobalISelEmitter.cpp
   InstrDocsEmitter.cpp
   InstrInfoEmitter.cpp
-  IntrinsicEmitter.cpp
   MacroFusionPredicatorEmitter.cpp
   OptionParserEmitter.cpp
   OptionRSTEmitter.cpp
   PseudoLoweringEmitter.cpp
   RegisterBankEmitter.cpp
   RegisterInfoEmitter.cpp
-  RISCVTargetDefEmitter.cpp
   SearchableTableEmitter.cpp
   SubtargetEmitter.cpp
-  TableGen.cpp
-  VTEmitter.cpp
   WebAssemblyDisassemblerEmitter.cpp
   X86InstrMappingEmitter.cpp
   X86DisassemblerTables.cpp
@@ -76,6 +69,8 @@ add_tablegen(llvm-tblgen LLVM
   X86MnemonicTables.cpp
   X86ModRMFilters.cpp
   X86RecognizableInstr.cpp
+
+  $<TARGET_OBJECTS:llvm-min-tblgen>
   $<TARGET_OBJECTS:obj.LLVMTableGenBasic>
   $<TARGET_OBJECTS:obj.LLVMTableGenCommon>
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/114494