[llvm] [RISCV] Simplify EEW/EMUL check in VLOptimizer. NFC (PR #152100)

[Luke Lau via llvm-commits]

https://github.com/lukel97 created https://github.com/llvm/llvm-project/pull/152100

Currently when checking to see if two OperandInfos are compatible, we check to see if the user operand only uses the first scalar and then do two different checks depending on that.

However whether or not the user only uses the first scalar is already encoded in OperandInfo, when EMUL is nullopt.

This removes the redundant check and keeps the logic in the OperandInfo class to make the callsite easier to reason about.


>From 6a20105a699324056bb33019fa77af04c76b8692 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Tue, 5 Aug 2025 15:05:49 +0800
Subject: [PATCH] [RISCV] Simplify EEW/EMUL check. NFC

Currently when checking to see if two OperandInfos are compatible, we check to see if the user operand only uses the first scalar and then do two different checks depending on that.

However whether or not the user only uses the first scalar is already encoded in OperandInfo, when EMUL is nullopt.

This removes the redundant check and keeps the logic in the OperandInfo class to make the callsite easier to reason about.
---
 llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp | 25 ++++++++++------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp b/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
index c9464515d2e56..37a71e8ec7689 100644
--- a/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
+++ b/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
@@ -69,6 +69,7 @@ struct OperandInfo {
   // Represent as 1,2,4,8, ... and fractional indicator. This is because
   // EMUL can take on values that don't map to RISCVVType::VLMUL values exactly.
   // For example, a mask operand can have an EMUL less than MF8.
+  // If nullopt, then EMUL isn't used (i.e. only a single scalar is read).
   std::optional<std::pair<unsigned, bool>> EMUL;
 
   unsigned Log2EEW;
@@ -83,12 +84,14 @@ struct OperandInfo {
 
   OperandInfo() = delete;
 
-  static bool EMULAndEEWAreEqual(const OperandInfo &A, const OperandInfo &B) {
-    return A.Log2EEW == B.Log2EEW && A.EMUL == B.EMUL;
-  }
-
-  static bool EEWAreEqual(const OperandInfo &A, const OperandInfo &B) {
-    return A.Log2EEW == B.Log2EEW;
+  /// Return true if the EMUL and EEW produced by \p Def is compatible with the
+  /// EMUL and EEW used by \p User.
+  static bool areCompatible(const OperandInfo &Def, const OperandInfo &User) {
+    if (Def.Log2EEW != User.Log2EEW)
+      return false;
+    if (User.EMUL && Def.EMUL != User.EMUL)
+      return false;
+    return true;
   }
 
   void print(raw_ostream &OS) const {
@@ -98,7 +101,7 @@ struct OperandInfo {
         OS << "f";
       OS << EMUL->first;
     } else
-      OS << "EMUL: unknown\n";
+      OS << "EMUL: none\n";
     OS << ", EEW: " << (1 << Log2EEW);
   }
 };
@@ -1399,13 +1402,7 @@ RISCVVLOptimizer::checkUsers(const MachineInstr &MI) const {
       return std::nullopt;
     }
 
-    // If the operand is used as a scalar operand, then the EEW must be
-    // compatible. Otherwise, the EMUL *and* EEW must be compatible.
-    bool IsVectorOpUsedAsScalarOp = isVectorOpUsedAsScalarOp(UserOp);
-    if ((IsVectorOpUsedAsScalarOp &&
-         !OperandInfo::EEWAreEqual(*ConsumerInfo, *ProducerInfo)) ||
-        (!IsVectorOpUsedAsScalarOp &&
-         !OperandInfo::EMULAndEEWAreEqual(*ConsumerInfo, *ProducerInfo))) {
+    if (!OperandInfo::areCompatible(*ProducerInfo, *ConsumerInfo)) {
       LLVM_DEBUG(
           dbgs()
           << "    Abort due to incompatible information for EMUL or EEW.\n");