[llvm] [SROA] Optimize reloaded values in allocas that escape into readonly nocapture calls. (PR #116645)

[Nikita Popov via llvm-commits]

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@@ -1390,14 +1394,31 @@ class AllocaSlices::SliceBuilder : public PtrUseVisitor<SliceBuilder> {
 
   /// Disable SROA entirely if there are unhandled users of the alloca.
   void visitInstruction(Instruction &I) { PI.setAborted(&I); }
+
+  void visitCallBase(CallBase &CB) {
+    // If the operands that are U are NoCapture ReadOnly, then we mark it as
+    // EscapedReadOnly.
+    Function *Callee = CB.getCalledFunction();
+    if (Callee && CB.arg_size() == Callee->arg_size() &&
+        !CB.hasOperandBundles() && all_of(enumerate(CB.args()), [&](auto V) {
+          return V.value() != *U ||
+                 (Callee->getArg(V.index())->hasNoCaptureAttr() &&
+                  Callee->getArg(V.index())->onlyReadsMemory());
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nikic wrote:

Please use the methods on CallBase instead, like `CB.doesNotCapture(Idx)`.

https://github.com/llvm/llvm-project/pull/116645