[PATCH] D25188: Fix nondeterministic output in local stack slot alloc pass

[Matt Arsenault via llvm-commits]

arsenm created this revision.
arsenm added a subscriber: llvm-commits.
Herald added a subscriber: wdng.

This finds all of the references to a frame index in a function, and
sorts by the offset. If multiple instructions use the same offset,
nothing was breaking the tie for sorting.

      

This avoids the test failures the reverted r282999 introduced.


https://reviews.llvm.org/D25188

Files:
  lib/CodeGen/LocalStackSlotAllocation.cpp


Index: lib/CodeGen/LocalStackSlotAllocation.cpp
===================================================================
--- lib/CodeGen/LocalStackSlotAllocation.cpp
+++ lib/CodeGen/LocalStackSlotAllocation.cpp
@@ -51,11 +51,19 @@
     MachineBasicBlock::iterator MI; // Instr referencing the frame
     int64_t LocalOffset;            // Local offset of the frame idx referenced
     int FrameIdx;                   // The frame index
+
+    // Order reference instruction appears in program. Used to ensure
+    // deterministic order when multiple instructions may reference the same
+    // location.
+    unsigned Order;
+
   public:
-    FrameRef(MachineBasicBlock::iterator I, int64_t Offset, int Idx) :
-      MI(I), LocalOffset(Offset), FrameIdx(Idx) {}
+    FrameRef(MachineInstr *I, int64_t Offset, int Idx, unsigned Ord) :
+      MI(I), LocalOffset(Offset), FrameIdx(Idx), Order(Ord) {}
     bool operator<(const FrameRef &RHS) const {
-      return LocalOffset < RHS.LocalOffset;
+      if (LocalOffset < RHS.LocalOffset)
+        return true;
+      return Order < RHS.Order;
     }
     MachineBasicBlock::iterator getMachineInstr() const { return MI; }
     int64_t getLocalOffset() const { return LocalOffset; }
@@ -285,6 +293,8 @@
   // choose the first one).
   SmallVector<FrameRef, 64> FrameReferenceInsns;
 
+  unsigned Order = 0;
+
   for (MachineBasicBlock &BB : Fn) {
     for (MachineInstr &MI : BB) {
       // Debug value, stackmap and patchpoint instructions can't be out of
@@ -311,7 +321,7 @@
           int64_t LocalOffset = LocalOffsets[Idx];
           if (!TRI->needsFrameBaseReg(&MI, LocalOffset))
             break;
-          FrameReferenceInsns.push_back(FrameRef(&MI, LocalOffset, Idx));
+          FrameReferenceInsns.push_back(FrameRef(&MI, LocalOffset, Idx, Order++));
           break;
         }
       }


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