[llvm] [AArch64] Add a fast-path for AArch64InstrInfo::getInstSizeInBytes (NFC) (PR #221894)

[Cullen Rhodes via llvm-commits]

https://github.com/c-rhodes updated https://github.com/llvm/llvm-project/pull/221894

>From be1403a1f2db85c9443fa8300fa8522561bea90a Mon Sep 17 00:00:00 2001
From: Cullen Rhodes <cullen.rhodes at arm.com>
Date: Tue, 28 Apr 2026 19:21:46 +0000
Subject: [PATCH 1/2] [AArch64] Add a fast-path for
 AArch64InstrInfo::getInstSizeInBytes (NFC)

Assisted-by: codex
---
 llvm/lib/Target/AArch64/AArch64InstrInfo.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
index e69336ea04857..35fc9a67e1304 100644
--- a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
@@ -204,6 +204,10 @@ static std::optional<unsigned> getLFIInstSizeInBytes(const MachineInstr &MI) {
 /// GetInstSize - Return the number of bytes of code the specified
 /// instruction may be.  This returns the maximum number of bytes.
 unsigned AArch64InstrInfo::getInstSizeInBytes(const MachineInstr &MI) const {
+  const MCInstrDesc &Desc = MI.getDesc();
+  if (!Desc.isPseudo() && !Subtarget.isLFI())
+    return 4;
+
   const MachineBasicBlock &MBB = *MI.getParent();
   const MachineFunction *MF = MBB.getParent();
   const Function &F = MF->getFunction();
@@ -222,7 +226,6 @@ unsigned AArch64InstrInfo::getInstSizeInBytes(const MachineInstr &MI) const {
   // FIXME: We currently only handle pseudoinstructions that don't get expanded
   //        before the assembly printer.
   unsigned NumBytes = 0;
-  const MCInstrDesc &Desc = MI.getDesc();
 
   // LFI rewriter expansions that supersede normal sizing.
   const auto &STI = MF->getSubtarget<AArch64Subtarget>();

>From ad2dae7afb1fc969eb93530f38398d7a3a3b926c Mon Sep 17 00:00:00 2001
From: Cullen Rhodes <cullen.rhodes at arm.com>
Date: Tue, 8 Sep 2026 08:04:59 +0000
Subject: [PATCH 2/2] address comments

---
 llvm/lib/Target/AArch64/AArch64InstrInfo.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
index 35fc9a67e1304..27c1be3f19096 100644
--- a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
@@ -205,8 +205,10 @@ static std::optional<unsigned> getLFIInstSizeInBytes(const MachineInstr &MI) {
 /// instruction may be.  This returns the maximum number of bytes.
 unsigned AArch64InstrInfo::getInstSizeInBytes(const MachineInstr &MI) const {
   const MCInstrDesc &Desc = MI.getDesc();
-  if (!Desc.isPseudo() && !Subtarget.isLFI())
+  if (!Desc.isPseudo() && !Subtarget.isLFI()) {
+    assert(Desc.getSize() == 4 && "Unexpected instruction size");
     return 4;
+  }
 
   const MachineBasicBlock &MBB = *MI.getParent();
   const MachineFunction *MF = MBB.getParent();