[llvm-branch-commits] [llvm] release/23.x: [RISCV] Fix crash in convertToVLMAX when AVL is an ADDI of a frame index (#212923) (PR #212960)

[via llvm-branch-commits]

https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/212960

Backport ef7f2f611993a4bc59e181d2bf8fc6269d7e1c7d

Requested by: @wangpc-pp

>From f3e51999c6629e38a3e6c1c3a44107a71a4fecf7 Mon Sep 17 00:00:00 2001
From: Pengcheng Wang <wangpengcheng.pp at bytedance.com>
Date: Thu, 30 Jul 2026 16:44:07 +0800
Subject: [PATCH] [RISCV] Fix crash in convertToVLMAX when AVL is an ADDI of a
 frame index (#212923)

`getConstant()` recognizes an AVL that is an immediate by checking
the opcode is `ADDI`, then reading the second operand and checking
if it is `X0`. However the second operand may be a frame index and
`getReg()` asserts with "This is not a register operand!".

We should guard the register access with `isReg()` before comparing
against `X0`.

Fixes #212797.

(cherry picked from commit ef7f2f611993a4bc59e181d2bf8fc6269d7e1c7d)
---
 llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp |  2 +-
 .../test/CodeGen/RISCV/rvv/vlmax-peephole.mir | 25 +++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/CodeGen/RISCV/rvv/vlmax-peephole.mir

diff --git a/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp b/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp
index aabfd5506789f..6071006882b31 100644
--- a/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp
+++ b/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp
@@ -105,7 +105,7 @@ RISCVVectorPeephole::getConstant(const MachineOperand &VL) const {
     return VL.getImm();
 
   MachineInstr *Def = MRI->getVRegDef(VL.getReg());
-  if (!Def || Def->getOpcode() != RISCV::ADDI ||
+  if (!Def || Def->getOpcode() != RISCV::ADDI || !Def->getOperand(1).isReg() ||
       Def->getOperand(1).getReg() != RISCV::X0)
     return std::nullopt;
   return Def->getOperand(2).getImm();
diff --git a/llvm/test/CodeGen/RISCV/rvv/vlmax-peephole.mir b/llvm/test/CodeGen/RISCV/rvv/vlmax-peephole.mir
new file mode 100644
index 0000000000000..d2c34b502941d
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/rvv/vlmax-peephole.mir
@@ -0,0 +1,25 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc %s -o - -mtriple=riscv64 -mattr=+v -run-pass=riscv-vector-peephole -verify-machineinstrs | FileCheck %s
+
+# The AVL is defined by an ADDI whose second operand is a frame index rather than
+# a register.
+
+---
+name: avl_addi_frameindex
+tracksRegLiveness: true
+stack:
+  - { id: 0, type: default, size: 1, alignment: 1 }
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: avl_addi_frameindex
+    ; CHECK: [[DEF:%[0-9]+]]:vr = IMPLICIT_DEF
+    ; CHECK-NEXT: [[DEF1:%[0-9]+]]:vr = IMPLICIT_DEF
+    ; CHECK-NEXT: [[ADDI:%[0-9]+]]:gprnox0 = ADDI %stack.0, 1
+    ; CHECK-NEXT: [[PseudoVADD_VV_M1_:%[0-9]+]]:vr = PseudoVADD_VV_M1 $noreg, [[DEF]], [[DEF1]], killed [[ADDI]] /* vl */, 5 /* e32 */, 0 /* tu, mu */
+    ; CHECK-NEXT: PseudoRET implicit [[PseudoVADD_VV_M1_]]
+    %0:vr = IMPLICIT_DEF
+    %1:vr = IMPLICIT_DEF
+    %2:gprnox0 = ADDI %stack.0, 1
+    %3:vr = PseudoVADD_VV_M1 $noreg, %0, %1, killed %2, 5 /* e32 */, 0 /* tu, mu */
+    PseudoRET implicit %3
+...