[PATCH] D19338: New code hoisting pass based on GVN (optimistic approach)

[David Majnemer via llvm-commits]

majnemer added a subscriber: majnemer.

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Comment at: llvm/lib/Transforms/Scalar/GVNHoist.cpp:137-152
@@ +136,18 @@
+public:
+  void insert(CallInst *Call, GVN::ValueTable &VN) {
+    if (Call->doesNotReturn() || !Call->doesNotThrow())
+      return;
+
+    // A call that doesNotAccessMemory is handled as a Scalar,
+    // onlyReadsMemory will be handled as a Load instruction,
+    // all other calls will be handled as stores.
+    unsigned V = VN.lookupOrAdd(Call);
+
+    if (Call->doesNotAccessMemory())
+      VNtoCallsScalars.insert(std::make_pair(V, Call));
+    else if (Call->onlyReadsMemory())
+      VNtoCallsLoads.insert(std::make_pair(V, Call));
+    else
+      VNtoCallsStores.insert(std::make_pair(V, Call));
+  }
+
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What if the call is to a function which divides by zero?  What would stop you from hoisting the call to it?

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Comment at: llvm/lib/Transforms/Scalar/GVNHoist.cpp:635-637
@@ +634,5 @@
+            continue;
+          if (!OptForMinSize && !Call->onlyReadsMemory())
+            CallWithSideEffect = true;
+          CI.insert(Call, VN);
+        } else if (!CallWithSideEffect && !isa<GetElementPtrInst>(&I1))
----------------
Likewise, you need to make sure that the call has no side effects which is different from it not mutating memory.


http://reviews.llvm.org/D19338