[llvm] [TableGen] Use StringMap in getValueType instead of StringSwitch (PR #213229)

[Manasij Mukherjee via llvm-commits]

https://github.com/manasij7479 updated https://github.com/llvm/llvm-project/pull/213229

>From 5f7fdb25bc75ba7b6461e9e04243219bec6e7028 Mon Sep 17 00:00:00 2001
From: Manasij Mukherjee <manasijm at nvidia.com>
Date: Fri, 31 Jul 2026 08:57:47 +0000
Subject: [PATCH 1/2] [TableGen] Use StringMap in getValueType instead of
 StringSwitch

StringSwitch is linear.
getValueType gets called often, identified by callgrind to be
responsible for 11% of the executed instructions for NVPTX -gen-dag-isel.
NVPTX and RISCV -gen-dag-isel become 20% and 15% faster respectively.
Modest 2-6% improvement for others.
---
 llvm/utils/TableGen/Common/CodeGenTarget.cpp | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/llvm/utils/TableGen/Common/CodeGenTarget.cpp b/llvm/utils/TableGen/Common/CodeGenTarget.cpp
index 908c4392f1352..f1be77f7e85c2 100644
--- a/llvm/utils/TableGen/Common/CodeGenTarget.cpp
+++ b/llvm/utils/TableGen/Common/CodeGenTarget.cpp
@@ -18,7 +18,7 @@
 #include "CodeGenRegisters.h"
 #include "CodeGenSchedule.h"
 #include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/StringSwitch.h"
+#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -43,12 +43,13 @@ static cl::opt<unsigned>
 /// Returns the MVT that the specified TableGen
 /// record corresponds to.
 MVT llvm::getValueType(const Record *Rec) {
-  return StringSwitch<MVT>(Rec->getValueAsString("LLVMName"))
+  static const StringMap<MVT> ValueTypes = {
 #define GET_VT_ATTR(Ty, Sz, Any, Int, FP, Vec, Sc, Tup, NF, NElem, EltTy)      \
-  .Case(#Ty, MVT::Ty)
+  {#Ty, MVT::Ty},
 #include "llvm/CodeGen/GenVT.inc"
 #undef GET_VT_ATTR
-      .Case("INVALID_SIMPLE_VALUE_TYPE", MVT::INVALID_SIMPLE_VALUE_TYPE);
+      {"INVALID_SIMPLE_VALUE_TYPE", MVT::INVALID_SIMPLE_VALUE_TYPE}};
+  return ValueTypes.lookup(Rec->getValueAsString("LLVMName"));
 }
 
 StringRef llvm::getEnumName(MVT T) {

>From 72858218d01e236e32253632db6228afc3eabc05 Mon Sep 17 00:00:00 2001
From: Manasij Mukherjee <manasijm at nvidia.com>
Date: Fri, 31 Jul 2026 17:09:03 +0000
Subject: [PATCH 2/2] Change to DenseMap

---
 llvm/utils/TableGen/Common/CodeGenTarget.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/utils/TableGen/Common/CodeGenTarget.cpp b/llvm/utils/TableGen/Common/CodeGenTarget.cpp
index f1be77f7e85c2..6965ee8c75b15 100644
--- a/llvm/utils/TableGen/Common/CodeGenTarget.cpp
+++ b/llvm/utils/TableGen/Common/CodeGenTarget.cpp
@@ -17,8 +17,8 @@
 #include "CodeGenInstruction.h"
 #include "CodeGenRegisters.h"
 #include "CodeGenSchedule.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -43,7 +43,7 @@ static cl::opt<unsigned>
 /// Returns the MVT that the specified TableGen
 /// record corresponds to.
 MVT llvm::getValueType(const Record *Rec) {
-  static const StringMap<MVT> ValueTypes = {
+  static const DenseMap<StringRef, MVT> ValueTypes = {
 #define GET_VT_ATTR(Ty, Sz, Any, Int, FP, Vec, Sc, Tup, NF, NElem, EltTy)      \
   {#Ty, MVT::Ty},
 #include "llvm/CodeGen/GenVT.inc"