Replace open-coded indirect load elimination loop (#4952)

Not only does this have issues with iterator invalidation, it also runs
out of bounds if the last element is erased. We should just use the
functions for doing this rather than worrying about how to implement it
correctly ourselves.

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Author: saagarjha

lib/Dialect/TritonGPU/Transforms/Pipeliner/MatmulLoopPipeline.cpp

@@ -538,17 +538,14 @@ scheduleLoads(scf::ForOp forOp, tt::CoarseSchedule &schedule,
   if (loadOpToIndLevelAndUse.empty())
     return {};
 
-  for (auto iter = loadOpToIndLevelAndUse.begin();
-       iter != loadOpToIndLevelAndUse.end();) {
-    auto iterNext = iter + 1;
-    if (std::get<1>(*iter) >= numStages - 1)
-      // We assume loads with different dist are assigned to different stages.
-      // If numStages is 2, we will have no stage available for indirect loads
-      // with dist >= 1. In general, when dist is equal to numStages - 1, we
-      // should not pipeline it.
-      loadOpToIndLevelAndUse.erase(iter);
-    iter = iterNext;
-  }
+  // We assume loads with different dist are assigned to different stages.
+  // If numStages is 2, we will have no stage available for indirect loads
+  // with dist >= 1. In general, when dist is equal to numStages - 1, we
+  // should not pipeline it.
+  auto it = llvm::remove_if(loadOpToIndLevelAndUse, [=](auto op) {
+    return std::get<1>(op) >= numStages - 1;
+  });
+  loadOpToIndLevelAndUse.erase(it, loadOpToIndLevelAndUse.end());
 
   // Check which loads are good for pipelining, and assign them
   // memory layouts.