[AMDGPU] Add VGPR copies post regalloc fix pass

Regalloc creates COPY instructions which do not formally use VALU.
That results in v_mov instructions displaced after exec mask modification.
One pass which do it is SIOptimizeExecMasking, but potentially it can be
done by other passes too.

This patch adds a pass immediately after regalloc to add implicit exec
use operand to all VGPR copy instructions.

Differential Revision: https://reviews.llvm.org/D28874

llvm-svn: 292956

4 files changed, 78 insertions, 0 deletions

diff --git a/llvm/lib/Target/AMDGPU/AMDGPU.h b/llvm/lib/Target/AMDGPU/AMDGPU.h
index 7b0a7f4b605..78876ab4f9e 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPU.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPU.h
@@ -60,6 +60,9 @@ extern char &SIShrinkInstructionsID;
 void initializeSIFixSGPRCopiesPass(PassRegistry &);
 extern char &SIFixSGPRCopiesID;
 
+void initializeSIFixVGPRCopiesPass(PassRegistry &);
+extern char &SIFixVGPRCopiesID;
+
 void initializeSILowerI1CopiesPass(PassRegistry &);
 extern char &SILowerI1CopiesID;
 
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
index d8a0c716279..06adb372305 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
@@ -86,6 +86,7 @@ extern "C" void LLVMInitializeAMDGPUTarget() {
   PassRegistry *PR = PassRegistry::getPassRegistry();
   initializeSILowerI1CopiesPass(*PR);
   initializeSIFixSGPRCopiesPass(*PR);
+  initializeSIFixVGPRCopiesPass(*PR);
   initializeSIFoldOperandsPass(*PR);
   initializeSIShrinkInstructionsPass(*PR);
   initializeSIFixControlFlowLiveIntervalsPass(*PR);
@@ -615,6 +616,7 @@ void GCNPassConfig::addOptimizedRegAlloc(FunctionPass *RegAllocPass) {
 }
 
 void GCNPassConfig::addPostRegAlloc() {
+  addPass(&SIFixVGPRCopiesID);
   addPass(&SIOptimizeExecMaskingID);
   TargetPassConfig::addPostRegAlloc();
 }
diff --git a/llvm/lib/Target/AMDGPU/CMakeLists.txt b/llvm/lib/Target/AMDGPU/CMakeLists.txt
index 02d441756c8..bbd06b19d63 100644
--- a/llvm/lib/Target/AMDGPU/CMakeLists.txt
+++ b/llvm/lib/Target/AMDGPU/CMakeLists.txt
@@ -68,6 +68,7 @@ add_llvm_target(AMDGPUCodeGen
   SIDebuggerInsertNops.cpp
   SIFixControlFlowLiveIntervals.cpp
   SIFixSGPRCopies.cpp
+  SIFixVGPRCopies.cpp
   SIFoldOperands.cpp
   SIFrameLowering.cpp
   SIInsertSkips.cpp
diff --git a/llvm/lib/Target/AMDGPU/SIFixVGPRCopies.cpp b/llvm/lib/Target/AMDGPU/SIFixVGPRCopies.cpp
new file mode 100644
index 00000000000..3d3121788b5
--- /dev/null
+++ b/llvm/lib/Target/AMDGPU/SIFixVGPRCopies.cpp
@@ -0,0 +1,72 @@
+//===-- SIFixVGPRCopies.cpp - Fix VGPR Copies after regalloc --------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file
+/// \brief Add implicit use of exec to vector register copies.
+///
+//===----------------------------------------------------------------------===//
+
+#include "AMDGPU.h"
+#include "AMDGPUSubtarget.h"
+#include "SIInstrInfo.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "si-fix-vgpr-copies"
+
+namespace {
+
+class SIFixVGPRCopies : public MachineFunctionPass {
+public:
+  static char ID;
+
+public:
+  SIFixVGPRCopies() : MachineFunctionPass(ID) {
+    initializeSIFixVGPRCopiesPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+  StringRef getPassName() const override { return "SI Fix VGPR copies"; }
+};
+
+} // End anonymous namespace.
+
+INITIALIZE_PASS(SIFixVGPRCopies, DEBUG_TYPE, "SI Fix VGPR copies", false, false)
+
+char SIFixVGPRCopies::ID = 0;
+
+char &llvm::SIFixVGPRCopiesID = SIFixVGPRCopies::ID;
+
+bool SIFixVGPRCopies::runOnMachineFunction(MachineFunction &MF) {
+  const SISubtarget &ST = MF.getSubtarget<SISubtarget>();
+  const SIRegisterInfo *TRI = ST.getRegisterInfo();
+  const SIInstrInfo *TII = ST.getInstrInfo();
+  bool Changed = false;
+
+  for (MachineBasicBlock &MBB : MF) {
+    for (MachineInstr &MI : MBB) {
+      switch (MI.getOpcode()) {
+      case AMDGPU::COPY:
+        if (TII->isVGPRCopy(MI) && !MI.readsRegister(AMDGPU::EXEC, TRI)) {
+          MI.addOperand(MF,
+                        MachineOperand::CreateReg(AMDGPU::EXEC, false, true));
+          DEBUG(dbgs() << "Add exec use to " << MI);
+          Changed = true;
+        }
+        break;
+      default:
+        break;
+      }
+    }
+  }
+
+  return Changed;
+}