[ARM] Allow distributing postinc with PHI uses

Although this doesn't usually come up, we can have uses of the
BaseAccess of a distributed postinc being a PHI. This doesn't need the
usual dominance check as we will dominate along the phi edge, allowing
us to still create a postinc load/store.

Differential Revision: https://reviews.llvm.org/D127676

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp b/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
index fb9d686..0a38f56 100644
--- a/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
+++ b/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
@@ -2896,10 +2896,12 @@ bool ARMPreAllocLoadStoreOpt::DistributeIncrements(Register Base) {
     LLVM_DEBUG(dbgs() << "\nAttempting to distribute increments on VirtualReg "
                       << Base.virtRegIndex() << "\n");
 
-    // Make sure that Increment has no uses before BaseAccess.
+    // Make sure that Increment has no uses before BaseAccess that are not PHI
+    // uses.
     for (MachineInstr &Use :
         MRI->use_nodbg_instructions(Increment->getOperand(0).getReg())) {
-      if (!DT->dominates(BaseAccess, &Use) || &Use == BaseAccess) {
+      if (&Use == BaseAccess || (Use.getOpcode() != TargetOpcode::PHI &&
+                                 !DT->dominates(BaseAccess, &Use))) {
         LLVM_DEBUG(dbgs() << "  BaseAccess doesn't dominate use of increment\n");
         return false;
       }