[PATCH] D146192: [RISCV] Add an empty block after outlined MBB

[Wang Pengcheng via Phabricator via llvm-commits]

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So that MCP won't delete any copy instructions where a register is
set that is intended to be live-out, since MCP assumes that all the
defs are live-out conservatively.

This is a fix for D146037 <https://reviews.llvm.org/D146037>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D146192

Files:
  llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
  llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
  llvm/test/CodeGen/RISCV/O3-pipeline.ll
  llvm/test/CodeGen/RISCV/machine-outliner-and-machine-copy-propagation.ll


Index: llvm/test/CodeGen/RISCV/machine-outliner-and-machine-copy-propagation.ll
===================================================================
--- llvm/test/CodeGen/RISCV/machine-outliner-and-machine-copy-propagation.ll
+++ llvm/test/CodeGen/RISCV/machine-outliner-and-machine-copy-propagation.ll
@@ -196,3 +196,4 @@
 ; RV64I-NEXT:    lui a0, 524288
 ; RV64I-NEXT:    mv a1, s0
 ; RV64I-NEXT:    jr t0
+; RV64I-NEXT:  # %bb.1:
Index: llvm/test/CodeGen/RISCV/O3-pipeline.ll
===================================================================
--- llvm/test/CodeGen/RISCV/O3-pipeline.ll
+++ llvm/test/CodeGen/RISCV/O3-pipeline.ll
@@ -166,7 +166,6 @@
 ; CHECK-NEXT:       Implement the 'patchable-function' attribute
 ; CHECK-NEXT:       Branch relaxation pass
 ; CHECK-NEXT:       RISCV Make Compressible
-; CHECK-NEXT:       Machine Copy Propagation Pass
 ; CHECK-NEXT:       Contiguously Lay Out Funclets
 ; CHECK-NEXT:       StackMap Liveness Analysis
 ; CHECK-NEXT:       Live DEBUG_VALUE analysis
@@ -177,6 +176,7 @@
 ; CHECK-NEXT:       Machine Optimization Remark Emitter
 ; CHECK-NEXT:       Stack Frame Layout Analysis
 ; CHECK-NEXT:       RISCV pseudo instruction expansion pass
+; CHECK-NEXT:       Machine Copy Propagation Pass
 ; CHECK-NEXT:       RISCV atomic pseudo instruction expansion pass
 ; CHECK-NEXT:       Lazy Machine Block Frequency Analysis
 ; CHECK-NEXT:       Machine Optimization Remark Emitter
Index: llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
+++ llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
@@ -337,19 +337,16 @@
 void RISCVPassConfig::addPreEmitPass() {
   addPass(&BranchRelaxationPassID);
   addPass(createRISCVMakeCompressibleOptPass());
-
-  // TODO: It would potentially be better to schedule copy propagation after
-  // expanding pseudos (in addPreEmitPass2). However, performing copy
-  // propagation after the machine outliner (which runs after addPreEmitPass)
-  // currently leads to incorrect code-gen, where copies to registers within
-  // outlined functions are removed erroneously.
-  if (TM->getOptLevel() >= CodeGenOpt::Default && EnableRISCVCopyPropagation)
-    addPass(createMachineCopyPropagationPass(true));
 }
 
 void RISCVPassConfig::addPreEmitPass2() {
   addPass(createRISCVExpandPseudoPass());
 
+  // Do the copy propagation after expanding pseudos because we may produce some
+  // MVs when expanding.
+  if (TM->getOptLevel() >= CodeGenOpt::Default && EnableRISCVCopyPropagation)
+    addPass(createMachineCopyPropagationPass(true));
+
   // Schedule the expansion of AMOs at the last possible moment, avoiding the
   // possibility for other passes to break the requirements for forward
   // progress in the LR/SC block.
Index: llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
+++ llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
@@ -2011,6 +2011,13 @@
     MachineBasicBlock &MBB, MachineFunction &MF,
     const outliner::OutlinedFunction &OF) const {
 
+  // FIXME: Add an empty successor so that MCP won't delete any copy
+  // instructions where a register is set that is intended to be live-out, since
+  // MCP assumes that all the defs are live-out conservatively.
+  MachineBasicBlock &EmptyMBB = *MF.CreateMachineBasicBlock();
+  MF.insert(MF.end(), &EmptyMBB);
+  MBB.addSuccessorWithoutProb(&EmptyMBB);
+
   // Strip out any CFI instructions
   bool Changed = true;
   while (Changed) {


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