[llvm] [InstCombine] Pull vector reverse through intrinsics (PR #146384)

[Philip Reames via llvm-commits]

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@@ -1456,6 +1456,45 @@ InstCombinerImpl::foldShuffledIntrinsicOperands(IntrinsicInst *II) {
   return new ShuffleVectorInst(NewIntrinsic, Mask);
 }
 
+/// If all arguments of the intrinsic are reverses, try to pull the reverse
+/// after the intrinsic.
+Value *InstCombinerImpl::foldReversedIntrinsicOperands(IntrinsicInst *II) {
+  if (!isTriviallyVectorizable(II->getIntrinsicID()) ||
+      !II->getCalledFunction()->isSpeculatable())
+    return nullptr;
+
+  // At least 1 operand must be a reverse with 1 use because we are creating 2
+  // instructions.
+  if (none_of(II->args(), [](Value *V) {
+        return match(V, m_OneUse(m_VecReverse(m_Value())));
+      }))
+    return nullptr;
+
+  Value *X;
+  Constant *C;
+  SmallVector<Value *> NewArgs;
+  for (Use &Arg : II->args()) {
+    if (isVectorIntrinsicWithScalarOpAtArg(II->getIntrinsicID(),
+                                           Arg.getOperandNo(), nullptr))
+      NewArgs.push_back(Arg);
+    else if (match(&Arg, m_VecReverse(m_Value(X))))
+      NewArgs.push_back(X);
+    else if (Value *Splat = getSplatValue(Arg))
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preames wrote:

Hm, since we're inserting a new splat, do we need the existing one to be one-use?  You do need to insert a new one instead of reusing because of possible undef/poison lanes.  

https://github.com/llvm/llvm-project/pull/146384