Interprocedural Register Allocation (IPRA): add a Transformation Pass

Adds a MachineFunctionPass that scans the body to find calls, and
update the register mask with the one saved by the
RegUsageInfoCollector analysis in PhysicalRegisterUsageInfo.

Patch by Vivek Pandya <vivekvpandya@gmail.com>

Differential Revision: http://reviews.llvm.org/D21180

llvm-svn: 272414

5 files changed, 172 insertions, 0 deletions

diff --git a/llvm/include/llvm/CodeGen/Passes.h b/llvm/include/llvm/CodeGen/Passes.h
index e2e8ed964df..cffbca311fb 100644
--- a/llvm/include/llvm/CodeGen/Passes.h
+++ b/llvm/include/llvm/CodeGen/Passes.h
@@ -365,6 +365,11 @@ namespace llvm {
   /// This pass is executed POST-RA to collect which physical registers are
   /// preserved by given machine function.
   FunctionPass *createRegUsageInfoCollector();
+
+  /// Return a MachineFunction pass that identifies call sites
+  /// and propagates register usage information of callee to caller
+  /// if available with PysicalRegisterUsageInfo pass.
+  FunctionPass *createRegUsageInfoPropPass();
 } // End llvm namespace
 
 /// Target machine pass initializer for passes with dependencies. Use with
diff --git a/llvm/lib/CodeGen/CMakeLists.txt b/llvm/lib/CodeGen/CMakeLists.txt
index 58f620d511d..03314889c8e 100644
--- a/llvm/lib/CodeGen/CMakeLists.txt
+++ b/llvm/lib/CodeGen/CMakeLists.txt
@@ -103,6 +103,7 @@ add_llvm_library(LLVMCodeGen
   RenameIndependentSubregs.cpp
   RegisterUsageInfo.cpp
   RegUsageInfoCollector.cpp
+  RegUsageInfoPropagate.cpp
   SafeStack.cpp
   ScheduleDAG.cpp
   ScheduleDAGInstrs.cpp
diff --git a/llvm/lib/CodeGen/RegUsageInfoPropagate.cpp b/llvm/lib/CodeGen/RegUsageInfoPropagate.cpp
new file mode 100644
index 00000000000..759566147cc
--- /dev/null
+++ b/llvm/lib/CodeGen/RegUsageInfoPropagate.cpp
@@ -0,0 +1,131 @@
+//=--- RegUsageInfoPropagate.cpp - Register Usage Informartion Propagation --=//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// This pass is required to take advantage of the interprocedural register
+/// allocation infrastructure.
+///
+/// This pass iterates through MachineInstrs in a given MachineFunction and at
+/// each callsite queries RegisterUsageInfo for RegMask (calculated based on
+/// actual register allocation) of the callee function, if the RegMask detail
+/// is available then this pass will update the RegMask of the call instruction.
+/// This updated RegMask will be used by the register allocator while allocating
+/// the current MachineFunction.
+///
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/RegisterUsageInfo.h"
+#include "llvm/IR/Module.h"
+#include "llvm/PassAnalysisSupport.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetMachine.h"
+#include <map>
+#include <string>
+
+namespace llvm {
+void initializeRegUsageInfoPropagationPassPass(PassRegistry &);
+}
+
+using namespace llvm;
+
+#define DEBUG_TYPE "ip-regalloc"
+
+#define RUIP_NAME "Register Usage Information Propagation"
+
+namespace {
+class RegUsageInfoPropagationPass : public MachineFunctionPass {
+
+public:
+  RegUsageInfoPropagationPass() : MachineFunctionPass(ID) {
+    PassRegistry &Registry = *PassRegistry::getPassRegistry();
+    initializeRegUsageInfoPropagationPassPass(Registry);
+  }
+
+  const char *getPassName() const override { return RUIP_NAME; }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+
+  static char ID;
+
+private:
+  static void setRegMask(MachineInstr &MI, const uint32_t *RegMask) {
+    for (MachineOperand &MO : MI.operands()) {
+      if (MO.isRegMask())
+        MO.setRegMask(RegMask);
+    }
+  }
+};
+} // end of anonymous namespace
+char RegUsageInfoPropagationPass::ID = 0;
+
+INITIALIZE_PASS_BEGIN(RegUsageInfoPropagationPass, "reg-usage-propagation",
+                      RUIP_NAME, false, false)
+INITIALIZE_PASS_DEPENDENCY(PhysicalRegisterUsageInfo)
+INITIALIZE_PASS_END(RegUsageInfoPropagationPass, "reg-usage-propagation",
+                    RUIP_NAME, false, false)
+
+FunctionPass *llvm::createRegUsageInfoPropPass() {
+  return new RegUsageInfoPropagationPass();
+}
+
+void RegUsageInfoPropagationPass::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addRequired<PhysicalRegisterUsageInfo>();
+  AU.setPreservesAll();
+  MachineFunctionPass::getAnalysisUsage(AU);
+}
+
+bool RegUsageInfoPropagationPass::runOnMachineFunction(MachineFunction &MF) {
+  const Module *M = MF.getFunction()->getParent();
+  PhysicalRegisterUsageInfo *PRUI = &getAnalysis<PhysicalRegisterUsageInfo>();
+
+  DEBUG(dbgs() << " ++++++++++++++++++++ " << getPassName()
+               << " ++++++++++++++++++++  \n");
+  DEBUG(dbgs() << "MachineFunction : " << MF.getName() << "\n");
+
+  bool Changed = false;
+
+  for (MachineBasicBlock &MBB : MF) {
+    for (MachineInstr &MI : MBB) {
+      if (!MI.isCall())
+        continue;
+      DEBUG(dbgs()
+            << "Call Instruction Before Register Usage Info Propagation : \n");
+      DEBUG(dbgs() << MI << "\n");
+
+      auto UpdateRegMask = [&](const Function *F) {
+        const auto *RegMask = PRUI->getRegUsageInfo(F);
+        if (!RegMask)
+          return;
+        setRegMask(MI, &(*RegMask)[0]);
+        Changed = true;
+      };
+
+      MachineOperand &Operand = MI.getOperand(0);
+      if (Operand.isGlobal())
+        UpdateRegMask(cast<Function>(Operand.getGlobal()));
+      else if (Operand.isSymbol())
+        UpdateRegMask(M->getFunction(Operand.getSymbolName()));
+
+      DEBUG(dbgs()
+            << "Call Instruction After Register Usage Info Propagation : \n");
+      DEBUG(dbgs() << MI << "\n");
+    }
+  }
+
+  DEBUG(dbgs() << " +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++"
+                  "++++++ \n");
+  return Changed;
+}
diff --git a/llvm/lib/CodeGen/TargetPassConfig.cpp b/llvm/lib/CodeGen/TargetPassConfig.cpp
index 3e7261a895f..1b30cc8ee54 100644
--- a/llvm/lib/CodeGen/TargetPassConfig.cpp
+++ b/llvm/lib/CodeGen/TargetPassConfig.cpp
@@ -538,6 +538,9 @@ void TargetPassConfig::addISelPrepare() {
 void TargetPassConfig::addMachinePasses() {
   AddingMachinePasses = true;
 
+  if (UseIPRA)
+    addPass(createRegUsageInfoPropPass());
+
   // Insert a machine instr printer pass after the specified pass.
   if (!StringRef(PrintMachineInstrs.getValue()).equals("") &&
       !StringRef(PrintMachineInstrs.getValue()).equals("option-unspecified")) {
diff --git a/llvm/test/CodeGen/Generic/ipra-transform.ll b/llvm/test/CodeGen/Generic/ipra-transform.ll
new file mode 100644
index 00000000000..362af881234
--- /dev/null
+++ b/llvm/test/CodeGen/Generic/ipra-transform.ll
@@ -0,0 +1,32 @@
+
+; RUN: llc < %s | FileCheck %s -check-prefix=NOIPRA
+; RUN: llc -enable-ipra < %s | FileCheck %s
+
+
+target triple = "x86_64-unknown-unknown"
+define void @bar1() {
+	ret void
+}
+define preserve_allcc void @foo()#0 {
+; Due to preserve_allcc foo() will save some registers at start of foo()
+; prefix NOIPRA will verify that.
+; NOIPRA-LABEL: foo:
+; NOIPRA: pushq	%r10
+; NOIPRA-NEXT: pushq %r9
+; NOIPRA-NEXT: pushq %r8
+; NOIPRA: callq bar1
+; When IPRA is present above registers will not be saved and that is verified
+; by prefix CHECK.
+; CHECK: foo:
+; CHECK-NOT: pushq %r10
+; CHECK-NOT: pushq %r9
+; CHECK-NOT: pushq %r8
+; CHECK: callq bar1
+	call void @bar1()
+	call void @bar2()
+	ret void
+}
+define void @bar2() {
+	ret void
+}
+attributes #0 = {nounwind}