[llvm-branch-commits] [llvm] release/21.x: [LoongArch] Add `isSafeToMove` hook to prevent unsafe instruction motion (#163725) (PR #166936)
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Fri Nov 7 05:21:30 PST 2025
https://github.com/llvmbot updated https://github.com/llvm/llvm-project/pull/166936
>From d04b00b38bc6073c3fd233b30ee02685c8ed2e58 Mon Sep 17 00:00:00 2001
From: hev <wangrui at loongson.cn>
Date: Fri, 7 Nov 2025 21:01:53 +0800
Subject: [PATCH] [LoongArch] Add `isSafeToMove` hook to prevent unsafe
instruction motion (#163725)
This patch introduces a new virtual method
`TargetInstrInfo::isSafeToMove()` to allow backends to control whether a
machine instruction can be safely moved by optimization passes.
The `BranchFolder` pass now respects this hook when hoisting common
code. By default, all instructions are considered safe to to move.
For LoongArch, `isSafeToMove()` is overridden to prevent
relocation-related instruction sequences (e.g. PC-relative addressing
and calls) from being broken by instruction motion. Correspondingly,
`isSchedulingBoundary()` is updated to reuse this logic for consistency.
Fixes #163681
(cherry picked from commit cdc3cb20543bcb574f08ab23bffe0699f7a9cdc8)
---
llvm/include/llvm/CodeGen/TargetInstrInfo.h | 11 +++++
llvm/lib/CodeGen/BranchFolding.cpp | 5 +++
.../Target/LoongArch/LoongArchInstrInfo.cpp | 45 +++++++++++--------
.../lib/Target/LoongArch/LoongArchInstrInfo.h | 3 ++
4 files changed, 46 insertions(+), 18 deletions(-)
diff --git a/llvm/include/llvm/CodeGen/TargetInstrInfo.h b/llvm/include/llvm/CodeGen/TargetInstrInfo.h
index b5b83c7ff1164..4d6e34bf4e3a1 100644
--- a/llvm/include/llvm/CodeGen/TargetInstrInfo.h
+++ b/llvm/include/llvm/CodeGen/TargetInstrInfo.h
@@ -1730,6 +1730,17 @@ class LLVM_ABI TargetInstrInfo : public MCInstrInfo {
return true;
}
+ /// Return true if it's safe to move a machine instruction.
+ /// This allows the backend to prevent certain special instruction
+ /// sequences from being broken by instruction motion in optimization
+ /// passes.
+ /// By default, this returns true for every instruction.
+ virtual bool isSafeToMove(const MachineInstr &MI,
+ const MachineBasicBlock *MBB,
+ const MachineFunction &MF) const {
+ return true;
+ }
+
/// Test if the given instruction should be considered a scheduling boundary.
/// This primarily includes labels and terminators.
virtual bool isSchedulingBoundary(const MachineInstr &MI,
diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp
index 3b3e7a418feb5..2886a1b7c9e02 100644
--- a/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/llvm/lib/CodeGen/BranchFolding.cpp
@@ -1971,6 +1971,7 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
MachineBasicBlock::iterator FIB = FBB->begin();
MachineBasicBlock::iterator TIE = TBB->end();
MachineBasicBlock::iterator FIE = FBB->end();
+ MachineFunction &MF = *MBB->getParent();
while (TIB != TIE && FIB != FIE) {
// Skip dbg_value instructions. These do not count.
TIB = skipDebugInstructionsForward(TIB, TIE, false);
@@ -1985,6 +1986,10 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
// Hard to reason about register liveness with predicated instruction.
break;
+ if (!TII->isSafeToMove(*TIB, MBB, MF))
+ // Don't hoist the instruction if it isn't safe to move.
+ break;
+
bool IsSafe = true;
for (MachineOperand &MO : TIB->operands()) {
// Don't attempt to hoist instructions with register masks.
diff --git a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp
index 26d36f1c5058f..75a230268bf58 100644
--- a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp
+++ b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp
@@ -378,12 +378,9 @@ bool LoongArchInstrInfo::isBranchOffsetInRange(unsigned BranchOp,
}
}
-bool LoongArchInstrInfo::isSchedulingBoundary(const MachineInstr &MI,
- const MachineBasicBlock *MBB,
- const MachineFunction &MF) const {
- if (TargetInstrInfo::isSchedulingBoundary(MI, MBB, MF))
- return true;
-
+bool LoongArchInstrInfo::isSafeToMove(const MachineInstr &MI,
+ const MachineBasicBlock *MBB,
+ const MachineFunction &MF) const {
auto MII = MI.getIterator();
auto MIE = MBB->end();
@@ -429,25 +426,25 @@ bool LoongArchInstrInfo::isSchedulingBoundary(const MachineInstr &MI,
auto MO2 = Lu32I->getOperand(2).getTargetFlags();
if (MO0 == LoongArchII::MO_PCREL_HI && MO1 == LoongArchII::MO_PCREL_LO &&
MO2 == LoongArchII::MO_PCREL64_LO)
- return true;
+ return false;
if ((MO0 == LoongArchII::MO_GOT_PC_HI || MO0 == LoongArchII::MO_LD_PC_HI ||
MO0 == LoongArchII::MO_GD_PC_HI) &&
MO1 == LoongArchII::MO_GOT_PC_LO && MO2 == LoongArchII::MO_GOT_PC64_LO)
- return true;
+ return false;
if (MO0 == LoongArchII::MO_IE_PC_HI && MO1 == LoongArchII::MO_IE_PC_LO &&
MO2 == LoongArchII::MO_IE_PC64_LO)
- return true;
+ return false;
if (MO0 == LoongArchII::MO_DESC_PC_HI &&
MO1 == LoongArchII::MO_DESC_PC_LO &&
MO2 == LoongArchII::MO_DESC64_PC_LO)
- return true;
+ return false;
break;
}
case LoongArch::LU52I_D: {
auto MO = MI.getOperand(2).getTargetFlags();
if (MO == LoongArchII::MO_PCREL64_HI || MO == LoongArchII::MO_GOT_PC64_HI ||
MO == LoongArchII::MO_IE_PC64_HI || MO == LoongArchII::MO_DESC64_PC_HI)
- return true;
+ return false;
break;
}
default:
@@ -487,7 +484,7 @@ bool LoongArchInstrInfo::isSchedulingBoundary(const MachineInstr &MI,
auto MO1 = LoongArchII::getDirectFlags(SecondOp->getOperand(2));
auto MO2 = LoongArchII::getDirectFlags(Ld->getOperand(2));
if (MO1 == LoongArchII::MO_DESC_PC_LO && MO2 == LoongArchII::MO_DESC_LD)
- return true;
+ return false;
break;
}
if (SecondOp == MIE ||
@@ -496,34 +493,34 @@ bool LoongArchInstrInfo::isSchedulingBoundary(const MachineInstr &MI,
auto MO1 = LoongArchII::getDirectFlags(SecondOp->getOperand(2));
if (MO0 == LoongArchII::MO_PCREL_HI && SecondOp->getOpcode() == AddiOp &&
MO1 == LoongArchII::MO_PCREL_LO)
- return true;
+ return false;
if (MO0 == LoongArchII::MO_GOT_PC_HI && SecondOp->getOpcode() == LdOp &&
MO1 == LoongArchII::MO_GOT_PC_LO)
- return true;
+ return false;
if ((MO0 == LoongArchII::MO_LD_PC_HI ||
MO0 == LoongArchII::MO_GD_PC_HI) &&
SecondOp->getOpcode() == AddiOp && MO1 == LoongArchII::MO_GOT_PC_LO)
- return true;
+ return false;
break;
}
case LoongArch::ADDI_W:
case LoongArch::ADDI_D: {
auto MO = LoongArchII::getDirectFlags(MI.getOperand(2));
if (MO == LoongArchII::MO_PCREL_LO || MO == LoongArchII::MO_GOT_PC_LO)
- return true;
+ return false;
break;
}
case LoongArch::LD_W:
case LoongArch::LD_D: {
auto MO = LoongArchII::getDirectFlags(MI.getOperand(2));
if (MO == LoongArchII::MO_GOT_PC_LO)
- return true;
+ return false;
break;
}
case LoongArch::PseudoDESC_CALL: {
auto MO = LoongArchII::getDirectFlags(MI.getOperand(2));
if (MO == LoongArchII::MO_DESC_CALL)
- return true;
+ return false;
break;
}
default:
@@ -531,6 +528,18 @@ bool LoongArchInstrInfo::isSchedulingBoundary(const MachineInstr &MI,
}
}
+ return true;
+}
+
+bool LoongArchInstrInfo::isSchedulingBoundary(const MachineInstr &MI,
+ const MachineBasicBlock *MBB,
+ const MachineFunction &MF) const {
+ if (TargetInstrInfo::isSchedulingBoundary(MI, MBB, MF))
+ return true;
+
+ if (!isSafeToMove(MI, MBB, MF))
+ return true;
+
return false;
}
diff --git a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.h b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.h
index 63b7112b8b40a..282ea30b03299 100644
--- a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.h
+++ b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.h
@@ -64,6 +64,9 @@ class LoongArchInstrInfo : public LoongArchGenInstrInfo {
bool isBranchOffsetInRange(unsigned BranchOpc,
int64_t BrOffset) const override;
+ bool isSafeToMove(const MachineInstr &MI, const MachineBasicBlock *MBB,
+ const MachineFunction &MF) const override;
+
bool isSchedulingBoundary(const MachineInstr &MI,
const MachineBasicBlock *MBB,
const MachineFunction &MF) const override;
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