[Attributor] Fixup block addresses after rewriting function signature

[jdoerfert]

LGTM. thx

llvm/lib/Transforms/IPO/Attributor.cpp

NewFn->setAttributes(AttributeList::get(
         OldFnAttributeList.getRetAttributes(), NewArgumentAttributes));
 
     // Since we have now created the new function, splice the body of the old
     // function right into the new function, leaving the old rotting hulk of the
     // function empty.
     NewFn->getBasicBlockList().splice(NewFn->begin(),
                                       OldFn->getBasicBlockList());
 
+    // Fixup block addresses to reference new function.
+    SmallVector<BlockAddress *, 8u> BlockAddresses;
+    for (User *U : OldFn->users())
+      if (auto *BA = dyn_cast<BlockAddress>(U))
+        BlockAddresses.push_back(BA);
+    for (auto *BA : BlockAddresses)
+      BA->replaceAllUsesWith(BlockAddress::get(NewFn, BA->getBasicBlock()));
+
     // Set of all "call-like" instructions that invoke the old function mapped
     // to their new replacements.
     SmallVector<std::pair<CallBase *, CallBase *>, 8> CallSitePairs;
 
     // Callback to create a new "call-like" instruction for a given one.
     auto CallSiteReplacementCreator = [&](AbstractCallSite ACS) {
       CallBase *OldCB = cast<CallBase>(ACS.getInstruction());
       const AttributeList &OldCallAttributeList = OldCB->getAttributes();

llvm/test/Transforms/Attributor/misc_crash.ll

;
   %1 = tail call i32 (i32*, ...) bitcast (void (i32*)* @func2a to i32 (i32*, ...)*)(i32* @var2)
   br i1 %false, label %use_bb, label %ret_bb
 use_bb:
   ret i32 %1
 ret_bb:
   %2 = load i32, i32* @var2
   ret i32 %2
 }
+
+define void @func4() {
+; CHECK-LABEL: define {{[^@]+}}@func4
+; CHECK-NEXT:    call void @func5()
+; CHECK-NEXT:    ret void
+;
+  call void @func5(i32 0)
+  ret void
+}
+
+define internal void @func5(i32 %0) {
+; CHECK-LABEL: define {{[^@]+}}@func5
+; CHECK-NEXT:    [[TMP1:%.*]] = alloca i8*
+; CHECK-NEXT:    br label %block
+; CHECK:       block:
+; CHECK-NEXT:    store i8* blockaddress(@func5, %block), i8** [[TMP1]]
+; CHECK-NEXT:    [[TMP2:%.*]] = load i8*, i8** [[TMP1]]
+; CHECK-NEXT:    call void @func6(i8* [[TMP2]])
+; CHECK-NEXT:    ret void
+;
+  %tmp = alloca i8*
+  br label %block
+
+block:
+  store i8* blockaddress(@func5, %block), i8** %tmp
+  %addr = load i8*, i8** %tmp
+  call void @func6(i8* %addr)
+  ret void
+}
+
+; CHECK-LABEL: declare {{[^@]+}}@func6
+; CHECK-SAME: (i8*)
+declare void @func6(i8*)