[Exegesis][RISCV] Remove the usage of RISCVSubtarget

[mshockwave]

Replace the usage of RISCVSubtarget in RISCVExegesisPreprocessingPass with an equivalent. Because including RISCVSubtarget.h might slow down the build speed by hindering the degree of parallelism for components outside LLVMRISCVCodeGen.

[llvmbot]

@llvm/pr-subscribers-tools-llvm-exegesis

@llvm/pr-subscribers-backend-risc-v

Author: Min-Yih Hsu (mshockwave)

Changes

Replace the usage of RISCVSubtarget in RISCVExegesisPreprocessingPass with an equivalent. Because including RISCVSubtarget.h might slow down the build speed by hindering the degree of parallelism for components outside LLVMRISCVCodeGen.

---

Full diff: https://github.com/llvm/llvm-project/pull/129568.diff

1 Files Affected:

• (modified) llvm/tools/llvm-exegesis/lib/RISCV/RISCVExegesisPreprocessing.cpp (+8-4)

diff --git a/llvm/tools/llvm-exegesis/lib/RISCV/RISCVExegesisPreprocessing.cpp b/llvm/tools/llvm-exegesis/lib/RISCV/RISCVExegesisPreprocessing.cpp
index 7f1cfd9ea52df..69a02e94ecb39 100644
--- a/llvm/tools/llvm-exegesis/lib/RISCV/RISCVExegesisPreprocessing.cpp
+++ b/llvm/tools/llvm-exegesis/lib/RISCV/RISCVExegesisPreprocessing.cpp
@@ -12,9 +12,10 @@
 #include "RISCV.h"
 #include "RISCVExegesisPasses.h"
 #include "RISCVRegisterInfo.h"
-#include "RISCVSubtarget.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/TargetInstrInfo.h"
+#include "llvm/MC/MCContext.h"
 
 using namespace llvm;
 
@@ -63,10 +64,13 @@ static bool processAVLOperand(MachineInstr &MI, MachineRegisterInfo &MRI,
 
 bool RISCVExegesisPreprocessing::runOnMachineFunction(MachineFunction &MF) {
   MachineRegisterInfo &MRI = MF.getRegInfo();
-  const auto &STI = MF.getSubtarget<RISCVSubtarget>();
-  if (!STI.hasVInstructions())
+  // We could have use RISCVSubtarget::hasVInstructions here but including
+  // RISCVSubtarget.h would serialize the build of components outside
+  // LLVMRISCVCodeGen.
+  const MCSubtargetInfo &STI = *MF.getContext().getSubtargetInfo();
+  if (!STI.hasFeature(RISCV::FeatureStdExtZve32x))
     return false;
-  const TargetInstrInfo &TII = *STI.getInstrInfo();
+  const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
 
   LLVM_DEBUG(MF.print(dbgs() << "===Before RISCVExegesisPoreprocessing===\n");
              dbgs() << "\n");

[topperc]

Isn't the dependency on RISCVMCTargetDesc.h through the RISCV.h the same issue?

[boomanaiden154]

Wouldn't the build ordering be defined by the CMake target dependencies and not what headers get included?

[topperc]

Yeah the RISCV part of llvm-exegesis already depends on RISCVCommonTableGen

[mshockwave]

@nico I assumed you raised the original concern when you're dealing with GN, how are dependencies in this case got resolved in GN?

[mshockwave]

@nico do you mind sharing how GN resolves dependencies? #129568 (comment)