From 59da2ddc9a1b150466e164f7811510b9a1751a96 Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper@sifive.com>
Date: Sun, 18 Apr 2021 14:10:06 -0700
Subject: [PATCH] [TableGen] Pass SmallVector to union_modes instead of
 returning a std::vector.

The number of modes is small so this should avoid a heap allocation.

Also replace std::set with SmallSet.
---
 utils/TableGen/CodeGenDAGPatterns.cpp | 19 ++++++++++++++-----
 utils/TableGen/InfoByHwMode.h         | 15 +++++++--------
 2 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/utils/TableGen/CodeGenDAGPatterns.cpp b/utils/TableGen/CodeGenDAGPatterns.cpp
index 47e1085b914..aee232e559e 100644
--- a/utils/TableGen/CodeGenDAGPatterns.cpp
+++ b/utils/TableGen/CodeGenDAGPatterns.cpp
@@ -466,7 +466,8 @@ bool TypeInfer::EnforceSmallerThan(TypeSetByHwMode &Small,
 
   assert(Small.hasDefault() && Big.hasDefault());
 
-  std::vector<unsigned> Modes = union_modes(Small, Big);
+  SmallVector<unsigned, 4> Modes;
+  union_modes(Small, Big, Modes);
 
   // 1. Only allow integer or floating point types and make sure that
   //    both sides are both integer or both floating point.
@@ -573,7 +574,9 @@ bool TypeInfer::EnforceVectorEltTypeIs(TypeSetByHwMode &Vec,
   if (Elem.empty())
     Changed |= EnforceScalar(Elem);
 
-  for (unsigned M : union_modes(Vec, Elem)) {
+  SmallVector<unsigned, 4> Modes;
+  union_modes(Vec, Elem, Modes);
+  for (unsigned M : Modes) {
     TypeSetByHwMode::SetType &V = Vec.get(M);
     TypeSetByHwMode::SetType &E = Elem.get(M);
 
@@ -656,7 +659,9 @@ bool TypeInfer::EnforceVectorSubVectorTypeIs(TypeSetByHwMode &Vec,
   if (Sub.empty())
     Changed |= EnforceVector(Sub);
 
-  for (unsigned M : union_modes(Vec, Sub)) {
+  SmallVector<unsigned, 4> Modes;
+  union_modes(Vec, Sub, Modes);
+  for (unsigned M : Modes) {
     TypeSetByHwMode::SetType &S = Sub.get(M);
     TypeSetByHwMode::SetType &V = Vec.get(M);
 
@@ -696,7 +701,9 @@ bool TypeInfer::EnforceSameNumElts(TypeSetByHwMode &V, TypeSetByHwMode &W) {
     return !Lengths.count(T.isVector() ? T.getVectorNumElements() : 0);
   };
 
-  for (unsigned M : union_modes(V, W)) {
+  SmallVector<unsigned, 4> Modes;
+  union_modes(V, W, Modes);
+  for (unsigned M : Modes) {
     TypeSetByHwMode::SetType &VS = V.get(M);
     TypeSetByHwMode::SetType &WS = W.get(M);
 
@@ -741,7 +748,9 @@ bool TypeInfer::EnforceSameSize(TypeSetByHwMode &A, TypeSetByHwMode &B) {
     return !Sizes.count(T.getSizeInBits());
   };
 
-  for (unsigned M : union_modes(A, B)) {
+  SmallVector<unsigned, 4> Modes;
+  union_modes(A, B, Modes);
+  for (unsigned M : Modes) {
     TypeSetByHwMode::SetType &AS = A.get(M);
     TypeSetByHwMode::SetType &BS = B.get(M);
     TypeSizeSet AN, BN;
diff --git a/utils/TableGen/InfoByHwMode.h b/utils/TableGen/InfoByHwMode.h
index 4233a581a63..c97add687ca 100644
--- a/utils/TableGen/InfoByHwMode.h
+++ b/utils/TableGen/InfoByHwMode.h
@@ -15,10 +15,10 @@
 #define LLVM_UTILS_TABLEGEN_INFOBYHWMODE_H
 
 #include "CodeGenHwModes.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/Support/MachineValueType.h"
 
 #include <map>
-#include <set>
 #include <string>
 #include <vector>
 
@@ -37,10 +37,10 @@ enum : unsigned {
 };
 
 template <typename InfoT>
-std::vector<unsigned> union_modes(const InfoByHwMode<InfoT> &A,
-                                  const InfoByHwMode<InfoT> &B) {
-  std::vector<unsigned> V;
-  std::set<unsigned> U;
+void union_modes(const InfoByHwMode<InfoT> &A,
+                 const InfoByHwMode<InfoT> &B,
+                 SmallVectorImpl<unsigned> &Modes) {
+  SmallSet<unsigned, 4> U;
   for (const auto &P : A)
     U.insert(P.first);
   for (const auto &P : B)
@@ -49,12 +49,11 @@ std::vector<unsigned> union_modes(const InfoByHwMode<InfoT> &A,
   bool HasDefault = false;
   for (unsigned M : U)
     if (M != DefaultMode)
-      V.push_back(M);
+      Modes.push_back(M);
     else
       HasDefault = true;
   if (HasDefault)
-    V.push_back(DefaultMode);
-  return V;
+    Modes.push_back(DefaultMode);
 }
 
 template <typename InfoT>