[llvm] [TableGen] Fix computeRegUnitLaneMasks for ad hoc aliasing (PR #79462)

[Jay Foad via llvm-commits]

https://github.com/jayfoad created https://github.com/llvm/llvm-project/pull/79462

With ad hoc aliasing (using the Aliases field in register definitions)
we can have subregisters with disjoint lane masks that nevertheless
share a regunit. In this case we need to take the union of their
lane masks, not the intersection.

This was inadvertently broken by https://reviews.llvm.org/D157864


>From 5cdd4ba70d9fca571372c341d8f091e378c08781 Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad at amd.com>
Date: Thu, 25 Jan 2024 15:33:06 +0000
Subject: [PATCH] [TableGen] Fix computeRegUnitLaneMasks for ad hoc aliasing

With ad hoc aliasing (using the Aliases field in register definitions)
we can have subregisters with disjoint lane masks that nevertheless
share a regunit. In this case we need to take the union of their
lane masks, not the intersection.

This was inadvertently broken by https://reviews.llvm.org/D157864
---
 llvm/utils/TableGen/CodeGenRegisters.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/llvm/utils/TableGen/CodeGenRegisters.cpp b/llvm/utils/TableGen/CodeGenRegisters.cpp
index d1abdb74ea4a982..b9d404aaee5fd79 100644
--- a/llvm/utils/TableGen/CodeGenRegisters.cpp
+++ b/llvm/utils/TableGen/CodeGenRegisters.cpp
@@ -2144,7 +2144,7 @@ void CodeGenRegBank::computeRegUnitLaneMasks() {
     // Create an initial lane mask for all register units.
     const auto &RegUnits = Register.getRegUnits();
     CodeGenRegister::RegUnitLaneMaskList RegUnitLaneMasks(
-        RegUnits.count(), LaneBitmask::getAll());
+        RegUnits.count(), LaneBitmask::getNone());
     // Iterate through SubRegisters.
     typedef CodeGenRegister::SubRegMap SubRegMap;
     const SubRegMap &SubRegs = Register.getSubRegs();
@@ -2163,7 +2163,7 @@ void CodeGenRegBank::computeRegUnitLaneMasks() {
         unsigned u = 0;
         for (unsigned RU : RegUnits) {
           if (SUI == RU) {
-            RegUnitLaneMasks[u] &= LaneMask;
+            RegUnitLaneMasks[u] |= LaneMask;
             assert(!Found);
             Found = true;
           }
@@ -2173,6 +2173,10 @@ void CodeGenRegBank::computeRegUnitLaneMasks() {
         assert(Found);
       }
     }
+    for (auto &Mask : RegUnitLaneMasks) {
+      if (Mask.none())
+        Mask = LaneBitmask::getAll();
+    }
     Register.setRegUnitLaneMasks(RegUnitLaneMasks);
   }
 }