Reapply "[MCA] Adding the CustomBehaviour class to llvm-mca".

The original change was pushed in main as commit f7a23ecece52.
It was then reverted by commit a04f01bab2 because it caused linker failures
on buildbots that don't build the AMDGPU target.

--

Some instructions are not defined well enough within the target’s scheduling
model for llvm-mca to be able to properly simulate its behaviour. The ideal
solution to this situation is to modify the scheduling model, but that’s not
always a viable strategy. Maybe other parts of the backend depend on that
instruction being modelled the way that it is. Or maybe the instruction is quite
complex and it’s difficult to fully capture its behaviour with tablegen. The
CustomBehaviour class (which I will refer to as CB frequently) is designed to
provide intuitive scaffolding for developers to implement the correct modelling
for these instructions.

More details are available in the original commit log message (f7a23ecece52).

Differential Revision: https://reviews.llvm.org/D104149

1 files changed, 57 insertions, 1 deletions

diff --git a/llvm/tools/llvm-mca/llvm-mca.cpp b/llvm/tools/llvm-mca/llvm-mca.cpp
index 3bb2f10..4e47762 100644
--- a/llvm/tools/llvm-mca/llvm-mca.cpp
+++ b/llvm/tools/llvm-mca/llvm-mca.cpp
@@ -32,6 +32,9 @@
 #include "Views/SchedulerStatistics.h"
 #include "Views/SummaryView.h"
 #include "Views/TimelineView.h"
+#ifdef HAS_AMDGPU
+#include "lib/AMDGPU/AMDGPUCustomBehaviour.h"
+#endif
 #include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCCodeEmitter.h"
@@ -42,6 +45,7 @@
 #include "llvm/MC/MCTargetOptionsCommandFlags.h"
 #include "llvm/MCA/CodeEmitter.h"
 #include "llvm/MCA/Context.h"
+#include "llvm/MCA/CustomBehaviour.h"
 #include "llvm/MCA/InstrBuilder.h"
 #include "llvm/MCA/Pipeline.h"
 #include "llvm/MCA/Stages/EntryStage.h"
@@ -220,6 +224,12 @@ static cl::opt<bool> ShowEncoding(
     cl::desc("Print encoding information in the instruction info view"),
     cl::cat(ViewOptions), cl::init(false));
 
+static cl::opt<bool> DisableCustomBehaviour(
+    "disable-cb",
+    cl::desc(
+        "Disable custom behaviour (use the default class which does nothing)."),
+    cl::cat(ViewOptions), cl::init(false));
+
 namespace {
 
 const Target *getTarget(const char *ProgName) {
@@ -285,6 +295,39 @@ static void processViewOptions(bool IsOutOfOrder) {
     processOptionImpl(PrintRetireStats, Default);
 }
 
+std::unique_ptr<mca::InstrPostProcess>
+createInstrPostProcess(const Triple &TheTriple, const MCSubtargetInfo &STI,
+                       const MCInstrInfo &MCII) {
+  // Might be a good idea to have a separate flag so that InstrPostProcess
+  // can be used with or without CustomBehaviour
+  if (DisableCustomBehaviour)
+    return std::make_unique<mca::InstrPostProcess>(STI, MCII);
+#ifdef HAS_AMDGPU
+  if (TheTriple.isAMDGPU())
+    return std::make_unique<mca::AMDGPUInstrPostProcess>(STI, MCII);
+#endif
+  return std::make_unique<mca::InstrPostProcess>(STI, MCII);
+}
+
+std::unique_ptr<mca::CustomBehaviour>
+createCustomBehaviour(const Triple &TheTriple, const MCSubtargetInfo &STI,
+                      const mca::SourceMgr &SrcMgr, const MCInstrInfo &MCII) {
+  // Build the appropriate CustomBehaviour object for the current target.
+  // The CustomBehaviour class should never depend on the source code,
+  // but it can depend on the list of mca::Instruction and any classes
+  // that can be built using just the target info. If you need extra
+  // information from the source code or the list of MCInst, consider
+  // adding that information to the mca::Instruction class and setting
+  // it during InstrBuilder::createInstruction().
+  if (DisableCustomBehaviour)
+    return std::make_unique<mca::CustomBehaviour>(STI, SrcMgr, MCII);
+#ifdef HAS_AMDGPU
+  if (TheTriple.isAMDGPU())
+    return std::make_unique<mca::AMDGPUCustomBehaviour>(STI, SrcMgr, MCII);
+#endif
+  return std::make_unique<mca::CustomBehaviour>(STI, SrcMgr, MCII);
+}
+
 // Returns true on success.
 static bool runPipeline(mca::Pipeline &P) {
   // Handle pipeline errors here.
@@ -498,6 +541,8 @@ int main(int argc, char **argv) {
     // Lower the MCInst sequence into an mca::Instruction sequence.
     ArrayRef<MCInst> Insts = Region->getInstructions();
     mca::CodeEmitter CE(*STI, *MAB, *MCE, Insts);
+    std::unique_ptr<mca::InstrPostProcess> IPP =
+        createInstrPostProcess(TheTriple, *STI, *MCII);
     std::vector<std::unique_ptr<mca::Instruction>> LoweredSequence;
     for (const MCInst &MCI : Insts) {
       Expected<std::unique_ptr<mca::Instruction>> Inst =
@@ -520,6 +565,8 @@ int main(int argc, char **argv) {
         return 1;
       }
 
+      IPP->postProcessInstruction(Inst.get(), MCI);
+
       LoweredSequence.emplace_back(std::move(Inst.get()));
     }
 
@@ -547,8 +594,17 @@ int main(int argc, char **argv) {
       continue;
     }
 
+    // Create the CustomBehaviour object for enforcing Target Specific
+    // behaviours and dependencies that aren't expressed well enough
+    // in the tablegen. CB cannot depend on the list of MCInst or
+    // the source code (but it can depend on the list of
+    // mca::Instruction or any objects that can be reconstructed
+    // from the target information).
+    std::unique_ptr<mca::CustomBehaviour> CB =
+        createCustomBehaviour(TheTriple, *STI, S, *MCII);
+
     // Create a basic pipeline simulating an out-of-order backend.
-    auto P = MCA.createDefaultPipeline(PO, S);
+    auto P = MCA.createDefaultPipeline(PO, S, *CB);
     mca::PipelinePrinter Printer(*P, PrintJson ? mca::View::OK_JSON
                                                : mca::View::OK_READABLE);