[Reduce] Argument reduction: do deal with function declarations

We can happily turn function definitions into declarations,
thus obscuring their argument from being elided by this pass.

I don't believe there is a good reason to just ignore declarations.
likely even proper llvm intrinsics ones,
at worst the input becomes uninteresting.

The other question here is that all these transforms are all-or-nothing.
In some cases, should we be treating each use separately?

The main blocker here seemed to be that llvm::CloneFunctionInto()
does `&OldFunc->front()`, which inserts a nullptr into a densemap,
which is not happy about it and asserts.

llvm/lib/Transforms/Utils/CloneFunction.cpp

@@ -147,6 +147,11 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
                      TypeMapper, Materializer));
   }
 
+  // Everything else beyond this point deals with function instructions,
+  // so if we are dealing with a function declaration, we're done.
+  if (OldFunc->isDeclaration())
+    return;
+
   // When we remap instructions, we want to avoid duplicating inlined
   // DISubprograms, so record all subprograms we find as we duplicate
   // instructions and then freeze them in the MD map.

llvm/test/Reduce/Inputs/remove-multiple-use-of-args-in-same-instruction.py

@@ -1,13 +0,0 @@
-import sys
-
-FunctionCallPresent = False
-
-input = open(sys.argv[1], "r")
-for line in input:
-  if "call void @use" in line:
-    FunctionCallPresent = True
-
-if FunctionCallPresent:
-  sys.exit(0) # Interesting!
-
-sys.exit(1)

llvm/test/Reduce/Inputs/remove-multiple-use-of-global-vars-in-same-instruction.py

@@ -1,13 +0,0 @@
-import sys
-
-FunctionCallPresent = False
-
-input = open(sys.argv[1], "r")
-for line in input:
-  if "call void @use" in line:
-    FunctionCallPresent = True
-
-if FunctionCallPresent:
-  sys.exit(0) # Interesting!
-
-sys.exit(1)

llvm/test/Reduce/remove-args-from-declaration.ll

@@ -0,0 +1,24 @@
+; 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-LABEL: @interesting(
+; CHECK-INTERESTINGNESS-SAME: i32
+; CHECK-FINAL: declare void @interesting(i32)
+declare void @interesting(i32 %uninteresting1, i32 %interesting, i32 %uninteresting2)
+
+; CHECK-INTERESTINGNESS-LABEL: @interesting2(
+; CHECK-INTERESTINGNESS-SAME: i32
+; CHECK-FINAL: declare void @interesting2(i32)
+declare void @interesting2(i32 %uninteresting1, i32 %interesting, i32 %uninteresting2)
+
+; CHECK-INTERESTINGNESS-LABEL: @callee(
+; CHECK-INTERESTINGNESS-SAME: i32 %interesting
+; CHECK-FINAL: define void @callee(i32 %interesting) {
+define void @callee(i32 %uninteresting1, i32 %interesting, i32 %uninteresting2) {
+; CHECK-INTERESTINGNESS: call void @interesting2(
+; CHECK-INTERESTINGNESS-SAME: i32 %interesting
+; CHECK-FINAL: call void @interesting2(i32 %interesting)
+  call void @interesting2(i32 %uninteresting1, i32 %interesting, i32 %uninteresting2)
+; CHECK-ALL: ret void
+  ret void
+}

llvm/test/Reduce/remove-multiple-use-of-args-in-same-instruction.ll

@@ -1,14 +1,15 @@
 ; Test that llvm-reduce can remove uninteresting function arguments from function definitions as well as their calls.
 ;
-; RUN: llvm-reduce --test %python --test-arg %p/Inputs/remove-multiple-use-of-args-in-same-instruction.py %s -o %t
-; RUN: cat %t | FileCheck -implicit-check-not=uninteresting %s
+; 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-ALL: declare void @use(i32, i32, i32)
 declare void @use(i32, i32, i32)
 
-; CHECK-LABEL: @interesting(i32 %uninteresting1, i32 %uninteresting2, i32 %uninteresting3
+; CHECK-ALL: @interesting(i32 %uninteresting1, i32 %uninteresting2, i32 %uninteresting3
 define void @interesting(i32 %uninteresting1, i32 %uninteresting2, i32 %uninteresting3) {
 entry:
-  ; CHECK: call void @use(i32 %uninteresting1, i32 %uninteresting2, i32 %uninteresting3)
+  ; CHECK-ALL: call void @use(i32 %uninteresting1, i32 %uninteresting2, i32 %uninteresting3)
   call void @use(i32 %uninteresting1, i32 %uninteresting2, i32 %uninteresting3)
   call void @use(i32 %uninteresting1, i32 %uninteresting2, i32 %uninteresting3)
   call void @use(i32 %uninteresting1, i32 %uninteresting2, i32 %uninteresting3)

llvm/test/Reduce/remove-multiple-use-of-global-vars-in-same-instruction.ll

@@ -1,11 +1,11 @@
 ; Test that llvm-reduce can remove uninteresting function arguments from function definitions as well as their calls.
 ;
-; RUN: llvm-reduce --test %python --test-arg %p/Inputs/remove-multiple-use-of-global-vars-in-same-instruction.py %s -o %t
-; RUN: cat %t | FileCheck -implicit-check-not=uninteresting %s
+; 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: @uninteresting1 = global
-; CHECK: @uninteresting2 = global
-; CHECK: @uninteresting3 = global
+; CHECK-ALL: @uninteresting1 = global
+; CHECK-ALL: @uninteresting2 = global
+; CHECK-ALL: @uninteresting3 = global
 @uninteresting1 = global i32 0, align 4
 @uninteresting2 = global i32 0, align 4
 @uninteresting3 = global i32 0, align 4
@@ -15,7 +15,7 @@ declare void @use(i32*, i32*, i32*)
 ; CHECK-LABEL: @interesting()
 define void @interesting() {
 entry:
-  ; CHECK: call void @use(i32* @uninteresting1, i32* @uninteresting2, i32* @uninteresting3)
+  ; CHECK-ALL: call void @use(i32* @uninteresting1, i32* @uninteresting2, i32* @uninteresting3)
   call void @use(i32* @uninteresting1, i32* @uninteresting2, i32* @uninteresting3)
   call void @use(i32* @uninteresting1, i32* @uninteresting2, i32* @uninteresting3)
   call void @use(i32* @uninteresting1, i32* @uninteresting2, i32* @uninteresting3)

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

@@ -48,7 +48,7 @@ static void extractArgumentsFromModule(std::vector<Chunk> ChunksToKeep,
   std::vector<Function *> Funcs;
   // Get inside-chunk arguments, as well as their parent function
   for (auto &F : *Program)
-    if (!F.isDeclaration()) {
+    if (!F.arg_empty()) {
       Funcs.push_back(&F);
       for (auto &A : F.args())
         if (O.shouldKeep())
@@ -108,7 +108,7 @@ static int countArguments(Module *Program) {
   outs() << "Param Index Reference:\n";
   int ArgsCount = 0;
   for (auto &F : *Program)
-    if (!F.isDeclaration() && F.arg_size()) {
+    if (!F.arg_empty()) {
       outs() << "  " << F.getName() << "\n";
       for (auto &A : F.args())
         outs() << "\t" << ++ArgsCount << ": " << A.getName() << "\n";