[llvm] [Attributor] Avoid AS-cast for function pointers (PR #65825)

[Johannes Doerfert via llvm-commits]

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@@ -12304,11 +12304,31 @@ struct AAIndirectCallInfoCallSite : public AAIndirectCallInfo {
                         UsedAssumedInformation))
       return ChangeStatus::UNCHANGED;
 
+    const auto *TTI =
+        A.getInfoCache().getAnalysisResultForFunction<TargetIRAnalysis>(
+            *CB->getFunction());
+    const DataLayout &DL = A.getDataLayout();
+    LLVMContext &Ctx = CB->getContext();
+
     ChangeStatus Changed = ChangeStatus::UNCHANGED;
     Value *FP = CB->getCalledOperand();
-    if (FP->getType()->getPointerAddressSpace())
-      FP = new AddrSpaceCastInst(FP, PointerType::get(FP->getType(), 0),
-                                 FP->getName() + ".as0", CB);
+    unsigned ProgramAS = A.getDataLayout().getProgramAddressSpace();
+    unsigned PtrAS = FP->getType()->getPointerAddressSpace();
+    // TODO: All we really want is a bitcast, see:
+    // https://github.com/llvm/llvm-project/commit/37642714edfc382be90ab8ec091e0261465c1b47#r126273142
+    if (PtrAS != ProgramAS) {
+      if (TTI->isNoopAddrSpaceCast(PtrAS, ProgramAS)) {
+        FP = new AddrSpaceCastInst(FP, PointerType::get(FP->getType(), 0),
+                                   FP->getName() + ".as0", CB);
+      } else {
+        FP = new IntToPtrInst(
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jdoerfert wrote:

If the AS cast is not a no-op, and this is not legal, we likely want to do nothing. How can I check for non-integral pointers to skip the generation of the if-cascade?

https://github.com/llvm/llvm-project/pull/65825