[llvm] [RISCV] fix RISCVPushPopOptimizer pass (PR #110236)

[via llvm-commits]

https://github.com/dlav-sc updated https://github.com/llvm/llvm-project/pull/110236

>From 7299365e9f30fdd41613352c1d7c48bc5f7c4aa6 Mon Sep 17 00:00:00 2001
From: Daniil Avdeev <daniil.avdeev at syntacore.com>
Date: Thu, 19 Sep 2024 17:41:57 +0000
Subject: [PATCH] [RISCV] fix RISCVPushPopOptimizer pass

RISCVPushPopOptimizer pass didn't suggest that CFI instructions can be
inserted between cm.pop and ret and couldn't apply optimization in these
cases. The patch fix it and allows the pass to remove CFI instructions and
combine cm.pop and ret into the one instruction: cm.popret or cm.popretz.
---
 .../Target/RISCV/RISCVPushPopOptimizer.cpp    | 29 ++++++++++++++++---
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVPushPopOptimizer.cpp b/llvm/lib/Target/RISCV/RISCVPushPopOptimizer.cpp
index 098e5bb5328bb3..c97bb3135f0d4f 100644
--- a/llvm/lib/Target/RISCV/RISCVPushPopOptimizer.cpp
+++ b/llvm/lib/Target/RISCV/RISCVPushPopOptimizer.cpp
@@ -45,10 +45,28 @@ char RISCVPushPopOpt::ID = 0;
 INITIALIZE_PASS(RISCVPushPopOpt, "riscv-push-pop-opt", RISCV_PUSH_POP_OPT_NAME,
                 false, false)
 
+template <typename IterT>
+static IterT nextNoDebugNoCFIInst(const IterT It, const IterT End) {
+  return std::find_if_not(std::next(It), End, [](const auto &Inst) {
+    return Inst.isDebugInstr() || Inst.isCFIInstruction() ||
+           Inst.isPseudoProbe();
+  });
+}
+
+static void eraseCFIInst(const MachineBasicBlock::iterator Begin,
+                         const MachineBasicBlock::iterator End) {
+  std::vector<std::reference_wrapper<llvm::MachineInstr>> CFIInstrs;
+  std::copy_if(std::next(Begin), End, std::back_inserter(CFIInstrs),
+               [](const auto &Inst) { return Inst.isCFIInstruction(); });
+
+  for (auto Inst : CFIInstrs)
+    Inst.get().eraseFromParent();
+}
+
 // Check if POP instruction was inserted into the MBB and return iterator to it.
 static MachineBasicBlock::iterator containsPop(MachineBasicBlock &MBB) {
   for (MachineBasicBlock::iterator MBBI = MBB.begin(); MBBI != MBB.end();
-       MBBI = next_nodbg(MBBI, MBB.end()))
+       MBBI = nextNoDebugNoCFIInst(MBBI, MBB.end()))
     if (MBBI->getOpcode() == RISCV::CM_POP)
       return MBBI;
 
@@ -76,6 +94,9 @@ bool RISCVPushPopOpt::usePopRet(MachineBasicBlock::iterator &MBBI,
   for (unsigned i = FirstNonDeclaredOp; i < MBBI->getNumOperands(); ++i)
     PopRetBuilder.add(MBBI->getOperand(i));
 
+  // Remove CFI instructions, they are not needed for cm.popret and cm.popretz
+  eraseCFIInst(MBBI, NextI);
+
   MBBI->eraseFromParent();
   NextI->eraseFromParent();
   return true;
@@ -92,8 +113,8 @@ bool RISCVPushPopOpt::adjustRetVal(MachineBasicBlock::iterator &MBBI) {
   // Since POP instruction is in Epilogue no normal instructions will follow
   // after it. Therefore search only previous ones to find the return value.
   for (MachineBasicBlock::reverse_iterator I =
-           next_nodbg(MBBI.getReverse(), RE);
-       I != RE; I = next_nodbg(I, RE)) {
+           nextNoDebugNoCFIInst(MBBI.getReverse(), RE);
+       I != RE; I = nextNoDebugNoCFIInst(I, RE)) {
     MachineInstr &MI = *I;
     if (auto OperandPair = TII->isCopyInstrImpl(MI)) {
       Register DestReg = OperandPair->Destination->getReg();
@@ -138,7 +159,7 @@ bool RISCVPushPopOpt::runOnMachineFunction(MachineFunction &Fn) {
   bool Modified = false;
   for (auto &MBB : Fn) {
     MachineBasicBlock::iterator MBBI = containsPop(MBB);
-    MachineBasicBlock::iterator NextI = next_nodbg(MBBI, MBB.end());
+    MachineBasicBlock::iterator NextI = nextNoDebugNoCFIInst(MBBI, MBB.end());
     if (MBBI != MBB.end() && NextI != MBB.end() &&
         NextI->getOpcode() == RISCV::PseudoRET)
       Modified |= usePopRet(MBBI, NextI, adjustRetVal(MBBI));