[llvm] [TableGen] Fix inconsistent indexing of the RegistersByName table. (PR #161835)

[Owen Anderson via llvm-commits]

https://github.com/resistor created https://github.com/llvm/llvm-project/pull/161835

Previously, the initialization of this table in CodeGenRegBank() indexed the table with the name of the tblgen def, while the only user of the table in CompressInstEmitter::validateRegister() indexed it using the name of the tblgen Def. Apparently these were the same essentially all of the time, so the issue never manifested. This patch standardizes on indexing using the tblgen def name, as that is guaranteed to be unique.

This issue impacted the forthcoming implementation of the RISC Y extension (CHERI), in which the capability registers have the same AsmName as the GPRs, causing llvm-tblgen assertion failures.


>From f68731c0ead4e244cd09ef1b729f27b2e9927c1c Mon Sep 17 00:00:00 2001
From: Owen Anderson <resistor at mac.com>
Date: Fri, 3 Oct 2025 21:23:10 +0900
Subject: [PATCH] [TableGen] Fix inconsistent indexing of the RegistersByName
 table.

Previously, the initialization of this table in CodeGenRegBank() indexed the table with the name of the tblgen def, while the only user of the table in CompressInstEmitter::validateRegister() indexed it using the name of the tblgen Def. Apparently these were the same essentially all of the time, so the issue never manifested. This patch standardizes on indexing using the tblgen def name, as that is guaranteed to be unique.

This issue impacted the forthcoming implementation of the RISC Y extension (CHERI), in which the capability registers have the same AsmName as the GPRs, causing llvm-tblgen assertion failures.
---
 llvm/utils/TableGen/Common/CodeGenRegisters.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/utils/TableGen/Common/CodeGenRegisters.cpp b/llvm/utils/TableGen/Common/CodeGenRegisters.cpp
index e873b3eaa4b7e..dd868cfa3eeae 100644
--- a/llvm/utils/TableGen/Common/CodeGenRegisters.cpp
+++ b/llvm/utils/TableGen/Common/CodeGenRegisters.cpp
@@ -1189,7 +1189,7 @@ CodeGenRegBank::CodeGenRegBank(const RecordKeeper &Records,
     // causes some failures in MIPS - perhaps they have duplicate register name
     // entries? (or maybe there's a reason for it - I don't know much about this
     // code, just drive-by refactoring)
-    RegistersByName.try_emplace(Reg.TheDef->getValueAsString("AsmName"), &Reg);
+    RegistersByName.try_emplace(Reg.getName().lower(), &Reg);
 
   // Precompute all sub-register maps.
   // This will create Composite entries for all inferred sub-register indices.