[llvm] [AMDGPU] Fix nondeterminism in SIFixSGPRCopies (PR #70644)

[Jay Foad via llvm-commits]

https://github.com/jayfoad created https://github.com/llvm/llvm-project/pull/70644

There are a couple of loops that iterate over V2SCopies. The iteration
order needs to be deterministic, otherwise we can call moveToVALU in
different orders, which causes temporary vregs to be allocated in
different orders, which can affect register allocation heuristics.


>From dcab0649eb6b9650e705643b90b6d9d347445fbc Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad at amd.com>
Date: Mon, 30 Oct 2023 10:40:22 +0000
Subject: [PATCH] [AMDGPU] Fix nondeterminism in SIFixSGPRCopies

There are a couple of loops that iterate over V2SCopies. The iteration
order needs to be deterministic, otherwise we can call moveToVALU in
different orders, which causes temporary vregs to be allocated in
different orders, which can affect register allocation heuristics.
---
 llvm/lib/Target/AMDGPU/SIFixSGPRCopies.cpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/SIFixSGPRCopies.cpp b/llvm/lib/Target/AMDGPU/SIFixSGPRCopies.cpp
index b32ed9fef5dd34e..3e6ed2d793ae563 100644
--- a/llvm/lib/Target/AMDGPU/SIFixSGPRCopies.cpp
+++ b/llvm/lib/Target/AMDGPU/SIFixSGPRCopies.cpp
@@ -125,7 +125,7 @@ class SIFixSGPRCopies : public MachineFunctionPass {
   SmallVector<MachineInstr*, 4> PHINodes;
   SmallVector<MachineInstr*, 4> S2VCopies;
   unsigned NextVGPRToSGPRCopyID;
-  DenseMap<unsigned, V2SCopyInfo> V2SCopies;
+  MapVector<unsigned, V2SCopyInfo> V2SCopies;
   DenseMap<MachineInstr *, SetVector<unsigned>> SiblingPenalty;
 
 public:
@@ -988,7 +988,7 @@ bool SIFixSGPRCopies::needToBeConvertedToVALU(V2SCopyInfo *Info) {
   for (auto J : Info->Siblings) {
     auto InfoIt = V2SCopies.find(J);
     if (InfoIt != V2SCopies.end()) {
-      MachineInstr *SiblingCopy = InfoIt->getSecond().Copy;
+      MachineInstr *SiblingCopy = InfoIt->second.Copy;
       if (SiblingCopy->isImplicitDef())
         // the COPY has already been MoveToVALUed
         continue;
@@ -1023,12 +1023,12 @@ void SIFixSGPRCopies::lowerVGPR2SGPRCopies(MachineFunction &MF) {
     unsigned CurID = LoweringWorklist.pop_back_val();
     auto CurInfoIt = V2SCopies.find(CurID);
     if (CurInfoIt != V2SCopies.end()) {
-      V2SCopyInfo C = CurInfoIt->getSecond();
+      V2SCopyInfo C = CurInfoIt->second;
       LLVM_DEBUG(dbgs() << "Processing ...\n"; C.dump());
       for (auto S : C.Siblings) {
         auto SibInfoIt = V2SCopies.find(S);
         if (SibInfoIt != V2SCopies.end()) {
-          V2SCopyInfo &SI = SibInfoIt->getSecond();
+          V2SCopyInfo &SI = SibInfoIt->second;
           LLVM_DEBUG(dbgs() << "Sibling:\n"; SI.dump());
           if (!SI.NeedToBeConvertedToVALU) {
             SI.SChain.set_subtract(C.SChain);