[llvm] LoopIdiomRecognize: detect and convert powi idiom (PR #72650)

[Joe Faulls via llvm-commits]

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@@ -549,33 +544,43 @@ bool LoopIdiomRecognize::runOnLoopBlock(
     BasicBlock *BB, const SCEV *BECount,
     SmallVectorImpl<BasicBlock *> &ExitBlocks) {
   // We can only promote stores in this block if they are unconditionally
-  // executed in the loop.  For a block to be unconditionally executed, it has
-  // to dominate all the exit blocks of the loop.  Verify this now.
+  // executed in the loop. The powi idiom also requires the block to be
+  // unconditionally executed. For a block to be unconditionally executed, it
+  // has to dominate all the exit blocks of the loop.
   for (BasicBlock *ExitBlock : ExitBlocks)
     if (!DT->dominates(BB, ExitBlock))
       return false;
 
   bool MadeChange = false;
-  // Look for store instructions, which may be optimized to memset/memcpy.
-  collectStores(BB);
 
-  // Look for a single store or sets of stores with a common base, which can be
-  // optimized into a memset (memset_pattern).  The latter most commonly happens
-  // with structs and handunrolled loops.
-  for (auto &SL : StoreRefsForMemset)
-    MadeChange |= processLoopStores(SL.second, BECount, ForMemset::Yes);
+  HasMemset = TLI->has(LibFunc_memset);
+  HasMemsetPattern = TLI->has(LibFunc_memset_pattern16);
+  HasMemcpy = TLI->has(LibFunc_memcpy);
+
+  if (HasMemset || HasMemsetPattern || HasMemcpy) {
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joe-img wrote:

This check doesn't really make sense to me. The functions called within this check can produce any of the above, yet we're only checking if we have at least one of them available?

Also, why wasn't there a check of this nature before?

https://github.com/llvm/llvm-project/pull/72650