[WebAssembly] Reintroduce ARGUMENT moving logic

Reinteroduce the code for moving ARGUMENTS back to the top of the basic block.
While the ARGUMENTS physical register prevents sinking and scheduling from
moving them, it does not appear to be sufficient to prevent SelectionDAG from
moving them down in the initial schedule. This patch introduces a patch that
moves them back to the top immediately after SelectionDAG runs.

This is still hopefully a temporary solution. http://reviews.llvm.org/D14750 is
one alternative, though the review has not been favorable, and proposed
alternatives are longer-term and have other downsides.

This fixes the main outstanding -verify-machineinstrs failures, so it adds
-verify-machineinstrs to several tests.

Differential Revision: http://reviews.llvm.org/D15377


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255125 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/WebAssembly/CMakeLists.txt

@@ -11,6 +11,7 @@ add_public_tablegen_target(WebAssemblyCommonTableGen)
 
 add_llvm_target(WebAssemblyCodeGen
   Relooper.cpp
+  WebAssemblyArgumentMove.cpp
   WebAssemblyAsmPrinter.cpp
   WebAssemblyCFGStackify.cpp
   WebAssemblyFastISel.cpp

lib/Target/WebAssembly/WebAssembly.h

@@ -27,6 +27,7 @@ FunctionPass *createWebAssemblyOptimizeReturned();
 
 FunctionPass *createWebAssemblyISelDag(WebAssemblyTargetMachine &TM,
                                        CodeGenOpt::Level OptLevel);
+FunctionPass *createWebAssemblyArgumentMove();
 
 FunctionPass *createWebAssemblyStoreResults();
 FunctionPass *createWebAssemblyRegStackify();

lib/Target/WebAssembly/WebAssemblyArgumentMove.cpp

@@ -0,0 +1,110 @@
+//===-- WebAssemblyArgumentMove.cpp - Argument instruction moving ---------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief This file moves ARGUMENT instructions after ScheduleDAG scheduling.
+///
+/// Arguments are really live-in registers, however, since we use virtual
+/// registers and LLVM doesn't support live-in virtual registers, we're
+/// currently making do with ARGUMENT instructions which are placed at the top
+/// of the entry block. The trick is to get them to *stay* at the top of the
+/// entry block.
+///
+/// The ARGUMENTS physical register keeps these instructions pinned in place
+/// during liveness-aware CodeGen passes, however one thing which does not
+/// respect this is the ScheduleDAG scheduler. This pass is therefore run
+/// immediately after that.
+///
+/// This is all hopefully a temporary solution until we find a better solution
+/// for describing the live-in nature of arguments.
+///
+//===----------------------------------------------------------------------===//
+
+#include "WebAssembly.h"
+#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
+#include "WebAssemblyMachineFunctionInfo.h"
+#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "wasm-argument-move"
+
+namespace {
+class WebAssemblyArgumentMove final : public MachineFunctionPass {
+public:
+  static char ID; // Pass identification, replacement for typeid
+  WebAssemblyArgumentMove() : MachineFunctionPass(ID) {}
+
+  const char *getPassName() const override {
+    return "WebAssembly Argument Move";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    AU.addPreserved<MachineBlockFrequencyInfo>();
+    AU.addPreservedID(MachineDominatorsID);
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+};
+} // end anonymous namespace
+
+char WebAssemblyArgumentMove::ID = 0;
+FunctionPass *llvm::createWebAssemblyArgumentMove() {
+  return new WebAssemblyArgumentMove();
+}
+
+/// Test whether the given instruction is an ARGUMENT.
+static bool IsArgument(const MachineInstr *MI) {
+  switch (MI->getOpcode()) {
+  case WebAssembly::ARGUMENT_I32:
+  case WebAssembly::ARGUMENT_I64:
+  case WebAssembly::ARGUMENT_F32:
+  case WebAssembly::ARGUMENT_F64:
+    return true;
+  default:
+    return false;
+  }
+}
+
+bool WebAssemblyArgumentMove::runOnMachineFunction(MachineFunction &MF) {
+  DEBUG({
+    dbgs() << "********** Argument Move **********\n"
+           << "********** Function: " << MF.getName() << '\n';
+  });
+
+  bool Changed = false;
+  MachineBasicBlock &EntryMBB = MF.front();
+  MachineBasicBlock::iterator InsertPt = EntryMBB.end();
+
+  // Look for the first NonArg instruction.
+  for (auto MII = EntryMBB.begin(), MIE = EntryMBB.end(); MII != MIE; ++MII) {
+    MachineInstr *MI = MII;
+    if (!IsArgument(MI)) {
+      InsertPt = MII;
+      break;
+    }
+  }
+
+  // Now move any argument instructions later in the block
+  // to before our first NonArg instruction.
+  for (auto I = InsertPt, E = EntryMBB.end(); I != E; ++I) {
+    MachineInstr *MI = I;
+    if (IsArgument(MI)) {
+      EntryMBB.insert(InsertPt, MI->removeFromParent());
+      Changed = true;
+    }
+  }
+
+  return Changed;
+}

lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp

@@ -149,6 +149,10 @@ bool WebAssemblyPassConfig::addInstSelector() {
   (void)TargetPassConfig::addInstSelector();
   addPass(
       createWebAssemblyISelDag(getWebAssemblyTargetMachine(), getOptLevel()));
+  // Run the argument-move pass immediately after the ScheduleDAG scheduler
+  // so that we can fix up the ARGUMENT instructions before anything else
+  // sees them in the wrong place.
+  addPass(createWebAssemblyArgumentMove());
   return false;
 }
 

test/CodeGen/WebAssembly/dead-vreg.ll

@@ -1,4 +1,4 @@
-; RUN: llc < %s -asm-verbose=false | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -verify-machineinstrs | FileCheck %s
 
 ; Check that unused vregs aren't assigned registers.
 

test/CodeGen/WebAssembly/phi.ll

@@ -1,4 +1,4 @@
-; RUN: llc < %s -asm-verbose=false | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -verify-machineinstrs | FileCheck %s
 
 ; Test that phis are lowered.
 

test/CodeGen/WebAssembly/reg-stackify.ll

@@ -1,4 +1,4 @@
-; RUN: llc < %s -asm-verbose=false | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -verify-machineinstrs | FileCheck %s
 
 ; Test the register stackifier pass.
 

test/CodeGen/WebAssembly/switch.ll

@@ -1,4 +1,4 @@
-; RUN: llc < %s -asm-verbose=false -disable-block-placement | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -disable-block-placement -verify-machineinstrs | FileCheck %s
 
 ; Test switch instructions. Block placement is disabled because it reorders
 ; the blocks in a way that isn't interesting here.

test/CodeGen/WebAssembly/unreachable.ll

@@ -1,5 +1,5 @@
-; RUN: llc < %s -asm-verbose=false | FileCheck %s
-; RUN: llc < %s -asm-verbose=false -fast-isel | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -verify-machineinstrs | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -fast-isel -verify-machineinstrs | FileCheck %s
 
 ; Test that LLVM unreachable instruction and trap intrinsic are lowered to
 ; wasm unreachable

test/CodeGen/WebAssembly/varargs.ll

@@ -1,4 +1,4 @@
-; RUN: llc < %s -asm-verbose=false | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -verify-machineinstrs | FileCheck %s
 
 ; Test varargs constructs.