[llvm] [TableGen] Simplify computeUberWeights. NFC. (PR #143716)

[Jay Foad via llvm-commits]

https://github.com/jayfoad created https://github.com/llvm/llvm-project/pull/143716

Using RegUnitIterator made the code more complicated than having two
nested loops over each register and each register's regunits.


>From d17026d490bfb419c6f998e2cbc68187997ab897 Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad at amd.com>
Date: Wed, 11 Jun 2025 15:39:05 +0100
Subject: [PATCH] [TableGen] Simplify computeUberWeights. NFC.

Using RegUnitIterator made the code more complicated than having two
nested loops over each register and each register's regunits.
---
 .../TableGen/Common/CodeGenRegisters.cpp      | 29 ++++++++-----------
 1 file changed, 12 insertions(+), 17 deletions(-)

diff --git a/llvm/utils/TableGen/Common/CodeGenRegisters.cpp b/llvm/utils/TableGen/Common/CodeGenRegisters.cpp
index 5ec9b35379fa4..4d24eb3de1ed9 100644
--- a/llvm/utils/TableGen/Common/CodeGenRegisters.cpp
+++ b/llvm/utils/TableGen/Common/CodeGenRegisters.cpp
@@ -1849,26 +1849,21 @@ static void computeUberWeights(MutableArrayRef<UberRegSet> UberSets,
   // Skip the first unallocatable set.
   for (UberRegSet &S : UberSets.drop_front()) {
     // Initialize all unit weights in this set, and remember the max units/reg.
-    const CodeGenRegister *Reg = nullptr;
-    unsigned MaxWeight = 0, Weight = 0;
-    for (RegUnitIterator UnitI(S.Regs); UnitI.isValid(); ++UnitI) {
-      if (Reg != UnitI.getReg()) {
-        if (Weight > MaxWeight)
-          MaxWeight = Weight;
-        Reg = UnitI.getReg();
-        Weight = 0;
-      }
-      if (!RegBank.getRegUnit(*UnitI).Artificial) {
-        unsigned UWeight = RegBank.getRegUnit(*UnitI).Weight;
-        if (!UWeight) {
-          UWeight = 1;
-          RegBank.increaseRegUnitWeight(*UnitI, UWeight);
+    unsigned MaxWeight = 0;
+    for (const CodeGenRegister *R : S.Regs) {
+      unsigned Weight = 0;
+      for (unsigned U : R->getRegUnits()) {
+        if (!RegBank.getRegUnit(U).Artificial) {
+          unsigned UWeight = RegBank.getRegUnit(U).Weight;
+          if (!UWeight) {
+            UWeight = 1;
+            RegBank.increaseRegUnitWeight(U, UWeight);
+          }
+          Weight += UWeight;
         }
-        Weight += UWeight;
       }
+      MaxWeight = std::max(MaxWeight, Weight);
     }
-    if (Weight > MaxWeight)
-      MaxWeight = Weight;
     if (S.Weight != MaxWeight) {
       LLVM_DEBUG({
         dbgs() << "UberSet " << &S - UberSets.begin() << " Weight "