[Reduce] Argument reduction: shoe-horn new function into remaining uses of old function

Much like with function reduction, there may be remaining unhandled uses
of function, in particular in blockaddress. And in constants we can't
RAUW it with undef, because undef is not a function.
Instead, let's try to pretent that in the remaining cases, the new
signature didn't change, by bitcasting it.

A new (previously crashing) test case added.

Author: LebedevRI

llvm/test/Reduce/remove-function-arguments-of-funcs-used-in-blockaddress.ll

@@ -0,0 +1,30 @@
+; RUN: llvm-reduce --test FileCheck --test-arg --check-prefixes=CHECK-ALL,CHECK-INTERESTINGNESS --test-arg %s --test-arg --input-file %s -o %t
+; RUN: cat %t | FileCheck --check-prefixes=CHECK-ALL,CHECK-FINAL %s
+
+; CHECK-INTERESTINGNESS: define void @func(
+; CHECK-FINAL: define void @func()
+define void @func(i1 %arg) {
+; CHECK-ALL: bb:
+; CHECK-ALL: br label %bb4
+bb:
+  br label %bb4
+
+; CHECK-ALL: bb4
+bb4:
+; CHECK-INTERESTINGNESS; callbr void asm
+; CHECK-INTERESTINGNESS-SAME; blockaddress
+; CHECK-FINAL: callbr void asm sideeffect "", "X"(i8* blockaddress(@func, %bb11))
+; CHECK-ALL: to label %bb5 [label %bb11]
+  callbr void asm sideeffect "", "X"(i8* blockaddress(@func, %bb11))
+          to label %bb5 [label %bb11]
+
+; CHECK-ALL: bb5:
+; CHECK-ALL: br label %bb11
+bb5:
+  br label %bb11
+
+; CHECK-ALL: bb11:
+; CHECK-ALL: ret void
+bb11:
+  ret void
+}

llvm/test/Reduce/remove-invoked-functions.ll

@@ -23,7 +23,7 @@ define void @caller(i32 %arg) personality i8* bitcast (i32 (...)* @__gxx_persona
 ; CHECK-ALL: bb:
 bb:
 ; CHECK-INTERESTINGNESS: %i0 = invoke i32
-; CHECK-FINAL: %i0 = invoke i32 undef(i32 %arg)
+; CHECK-FINAL: %i0 = invoke i32 bitcast (i32 ()* @maybe_throwing_callee to i32 (i32)*)(i32 %arg)
 ; CHECK-ALL: to label %bb3 unwind label %bb1
   %i0 = invoke i32 @maybe_throwing_callee(i32 %arg)
           to label %bb3 unwind label %bb1

llvm/tools/llvm-reduce/deltas/ReduceArguments.cpp

@@ -94,7 +94,7 @@ static void extractArgumentsFromModule(std::vector<Chunk> ChunksToKeep,
     replaceFunctionCalls(*F, *ClonedFunc, ArgIndexesToKeep);
     // Rename Cloned Function to Old's name
     std::string FName = std::string(F->getName());
-    F->replaceAllUsesWith(UndefValue::get(F->getType()));
+    F->replaceAllUsesWith(ConstantExpr::getBitCast(ClonedFunc, F->getType()));
     F->eraseFromParent();
     ClonedFunc->setName(FName);
   }