[SCCP] Fix crash when function arg is a unused basic block's address

[bcl5980]

Summary

For now if Solver never touch a basic block, DTU will erase the basic block even if the basic block address is referenced by function args.
So check the kernel arg is block address or not, if it is we need to mark the basic block executable.

Fix #54238, #54251

[nikic]

Per the discussion on https://github.com/llvm/llvm-project/issues/54238, my understanding is that considering the block dead is okay semantically, so I'm not sure preventing that is the right fix here. Why does the "usual" replacement of the blockaddress with 1 not work here and crash instead?

[bcl5980]

OK, thanks for the review. I will close this revision

[nickdesaulniers]

The issue is in [runIPSCCP](https://github.com/llvm/llvm-project/blob/687d20de7ffc69dd4ecdb9808aeb6d3cffcf3871/llvm/lib/Transforms/Scalar/SCCP.cpp#L500-L533). We don't clean up uses of any BlockAddresses before deleting the BasicBlock that's dead. So we basically need to do the same transform that was observed here. I'm working on a fix.

[nickdesaulniers]

https://reviews.llvm.org/D121744

llvm/lib/Transforms/Utils/SCCPSolver.cpp

       if (AI->hasByValAttr() && !F->onlyReadsMemory()) {
         markOverdefined(&*AI);
         continue;
+      } else if (const BlockAddress *BA = dyn_cast<BlockAddress>(CAI)) {
+        markBlockExecutable(BA->getBasicBlock());
+      } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(CAI)) {
+        for (Value *Op : CE->operands()) {
+          const BlockAddress *BA = dyn_cast<BlockAddress>(Op);
+          if (BA != nullptr)
+            markBlockExecutable(BA->getBasicBlock());
+        }
       }
 
       if (auto *STy = dyn_cast<StructType>(AI->getType())) {

llvm/test/Transforms/SCCP/issue54238.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-attributes
+; RUN: opt -passes=ipsccp -S %s | FileCheck %s
+; https://github.com/llvm/llvm-project/issues/54238
+
+define i32 @main() {
+  call void @set_return_addr(i64* bitcast (i8* blockaddress(@main, %redirected) to i64*))
+  ret i32 0
+
+redirected:
+  ret i32 0
+}
+
+define internal void @set_return_addr(i64* %addr) {
+  %addr.addr = alloca i64*, i32 0, align 8
+; CHECK: redirected
+  store i64* %addr, i64** %addr.addr, align 8
+  ret void
+}