[llvm] [RISCV] Prefer alt opcode vectorirazion if unaligned vector mem accesses (PR #154153)

[Mikhail Gudim via llvm-commits]

https://github.com/mgudim created https://github.com/llvm/llvm-project/pull/154153

are supported.

>From b370e1d18df413530da95e358f9e48cd31335694 Mon Sep 17 00:00:00 2001
From: Mikhail Gudim <mgudim at ventanamicro.com>
Date: Mon, 18 Aug 2025 09:28:29 -0700
Subject: [PATCH] [RISCV] Prefer alt opcode vectorirazion if unaligned vector
 mem accesses are supported.

---
 llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp | 4 ++++
 llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h   | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
index 85b3059d87da7..f49c3ae9bdea3 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
@@ -2713,6 +2713,10 @@ unsigned RISCVTTIImpl::getMinTripCountTailFoldingThreshold() const {
   return RVVMinTripCount;
 }
 
+bool RISCVTTIImpl::preferAlternateOpcodeVectorization() const override {
+  return ST->enableUnalignedVectorMem();
+}
+
 TTI::AddressingModeKind
 RISCVTTIImpl::getPreferredAddressingMode(const Loop *L,
                                          ScalarEvolution *SE) const {
diff --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
index 6a1f4b3e3bedf..254908f97186c 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h
@@ -132,7 +132,7 @@ class RISCVTTIImpl final : public BasicTTIImplBase<RISCVTTIImpl> {
 
   unsigned getMaximumVF(unsigned ElemWidth, unsigned Opcode) const override;
 
-  bool preferAlternateOpcodeVectorization() const override { return false; }
+  bool preferAlternateOpcodeVectorization() const override;
 
   bool preferEpilogueVectorization() const override {
     // Epilogue vectorization is usually unprofitable - tail folding or