[llvm] [GlobalISel] Look between instructions to be matched (PR #101675)

[Matt Arsenault via llvm-commits]

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@@ -61,15 +61,44 @@ bool GIMatchTableExecutor::isBaseWithConstantOffset(
 
 bool GIMatchTableExecutor::isObviouslySafeToFold(MachineInstr &MI,
                                                  MachineInstr &IntoMI) const {
+  auto IntoMIIter = IntoMI.getIterator();
+
   // Immediate neighbours are already folded.
   if (MI.getParent() == IntoMI.getParent() &&
-      std::next(MI.getIterator()) == IntoMI.getIterator())
+      std::next(MI.getIterator()) == IntoMIIter)
     return true;
 
   // Convergent instructions cannot be moved in the CFG.
   if (MI.isConvergent() && MI.getParent() != IntoMI.getParent())
     return false;
 
-  return !MI.mayLoadOrStore() && !MI.mayRaiseFPException() &&
-         !MI.hasUnmodeledSideEffects() && MI.implicit_operands().empty();
+  if (!MI.mayLoadOrStore() && !MI.mayRaiseFPException() &&
+      !MI.hasUnmodeledSideEffects() && MI.implicit_operands().empty()) {
+    return true;
+  }
+
+  // If the load is simple, check instructions between MI and IntoMI
+  if (MI.mayLoad() && MI.getParent() == IntoMI.getParent()) {
+    if (MI.memoperands_empty())
+      return false;
+    auto &MMO = **(MI.memoperands_begin());
+    if (MMO.isAtomic() || MMO.isVolatile())
+      return false;
+
+    // Ensure instructions between MI and IntoMI are not affected when combined
+    unsigned Iter = 0;
+    const unsigned MaxIter = 20;
+    for (auto CurrMI = MI.getIterator(); CurrMI != IntoMIIter; ++CurrMI) {
+      if (CurrMI->isLoadFoldBarrier() || CurrMI->mayRaiseFPException() ||
+          !CurrMI->implicit_operands().empty())
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arsenm wrote:

All of these instruction predicates should be in a single function. I also don't understand why the cases down here are different than above? 

https://github.com/llvm/llvm-project/pull/101675