[llvm] [CodeGen] Avoid repeated hash lookups (NFC) (PR #128126)

[Kazu Hirata via llvm-commits]

https://github.com/kazutakahirata created https://github.com/llvm/llvm-project/pull/128126

This patch eliminates repeated hash lookups at three levels:

- RegToSlotIdx  of DenseMap
- Reloads       of DenseMap
- Reloads[MBB]  of SmallSet


>From e2c66e961d9792a58d7a86f8f882df98bf2c30d0 Mon Sep 17 00:00:00 2001
From: Kazu Hirata <kazu at google.com>
Date: Thu, 20 Feb 2025 09:03:26 -0800
Subject: [PATCH] [CodeGen] Avoid repeated hash lookups (NFC)

This patch eliminates repeated hash lookups at three levels:

- RegToSlotIdx  of DenseMap
- Reloads       of DenseMap
- Reloads[MBB]  of SmallSet
---
 .../CodeGen/FixupStatepointCallerSaved.cpp    | 19 +++++--------------
 1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/llvm/lib/CodeGen/FixupStatepointCallerSaved.cpp b/llvm/lib/CodeGen/FixupStatepointCallerSaved.cpp
index edb85d212a4d4..0d6ec8975689b 100644
--- a/llvm/lib/CodeGen/FixupStatepointCallerSaved.cpp
+++ b/llvm/lib/CodeGen/FixupStatepointCallerSaved.cpp
@@ -179,19 +179,11 @@ class RegReloadCache {
 public:
   RegReloadCache() = default;
 
-  // Record reload of Reg from FI in block MBB
-  void recordReload(Register Reg, int FI, const MachineBasicBlock *MBB) {
+  // Record reload of Reg from FI in block MBB if not present yet.
+  // Return true if the reload is successfully recorded.
+  bool tryRecordReload(Register Reg, int FI, const MachineBasicBlock *MBB) {
     RegSlotPair RSP(Reg, FI);
-    auto Res = Reloads[MBB].insert(RSP);
-    (void)Res;
-    assert(Res.second && "reload already exists");
-  }
-
-  // Does basic block MBB contains reload of Reg from FI?
-  bool hasReload(Register Reg, int FI, const MachineBasicBlock *MBB) {
-    RegSlotPair RSP(Reg, FI);
-    auto It = Reloads.find(MBB);
-    return It != Reloads.end() && It->second.count(RSP);
+    return Reloads[MBB].insert(RSP).second;
   }
 };
 
@@ -459,8 +451,7 @@ class StatepointState {
       LLVM_DEBUG(dbgs() << "Reloading " << printReg(Reg, &TRI) << " from FI "
                         << RegToSlotIdx[Reg] << " after statepoint\n");
 
-      if (EHPad && !RC.hasReload(Reg, RegToSlotIdx[Reg], EHPad)) {
-        RC.recordReload(Reg, RegToSlotIdx[Reg], EHPad);
+      if (EHPad && RC.tryRecordReload(Reg, RegToSlotIdx[Reg], EHPad)) {
         auto EHPadInsertPoint =
             EHPad->SkipPHIsLabelsAndDebug(EHPad->begin(), Reg);
         insertReloadBefore(Reg, EHPadInsertPoint, EHPad);