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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

Author: Jay Foad (jayfoad)

<details>
<summary>Changes</summary>

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.


---
Full diff: https://github.com/llvm/llvm-project/pull/70644.diff


1 Files Affected:

- (modified) llvm/lib/Target/AMDGPU/SIFixSGPRCopies.cpp (+4-4) 


``````````diff
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);

``````````

</details>


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