[llvm] dbca8aa - [WebAssembly] Use SetVector instead of SmallPtrSet in FixBrTableDefaults (#84418)

[via llvm-commits]

Author: Derek Schuff
Date: 2024-03-08T09:20:44-08:00
New Revision: dbca8aa1472b9140a68918b2615519dc7dad593f

URL: https://github.com/llvm/llvm-project/commit/dbca8aa1472b9140a68918b2615519dc7dad593f
DIFF: https://github.com/llvm/llvm-project/commit/dbca8aa1472b9140a68918b2615519dc7dad593f.diff

LOG: [WebAssembly] Use SetVector instead of SmallPtrSet in FixBrTableDefaults (#84418)

This pass inserts all the MBBs into a set and then iterates over them.
But when
the number of elements gets large enough, SmallPtrSet expands into a
hash table
which wouldn't have a deterministic iteration order since the elements
are
pointers. This results in nondeterministic jump table layouts.
Use SetVector instead for a deterministic iteration order.

Added: 
    

Modified: 
    llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp
index 495f19a7ccde55..4252fc1f55fc9f 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp
@@ -159,19 +159,21 @@ bool WebAssemblyFixBrTableDefaults::runOnMachineFunction(MachineFunction &MF) {
                     << MF.getName() << '\n');
 
   bool Changed = false;
-  SmallPtrSet<MachineBasicBlock *, 16> MBBSet;
+  SetVector<MachineBasicBlock *, SmallVector<MachineBasicBlock *, 16>,
+            DenseSet<MachineBasicBlock *>, 16>
+      MBBSet;
   for (auto &MBB : MF)
     MBBSet.insert(&MBB);
 
   while (!MBBSet.empty()) {
     MachineBasicBlock *MBB = *MBBSet.begin();
-    MBBSet.erase(MBB);
+    MBBSet.remove(MBB);
     for (auto &MI : *MBB) {
       if (WebAssembly::isBrTable(MI.getOpcode())) {
         fixBrTableIndex(MI, MBB, MF);
         auto *Fixed = fixBrTableDefault(MI, MBB, MF);
         if (Fixed != nullptr) {
-          MBBSet.erase(Fixed);
+          MBBSet.remove(Fixed);
           Changed = true;
         }
         break;