Remove function hacky activity (rust-lang#701)

Author: wsmoses

enzyme/Enzyme/ActivityAnalysis.cpp

@@ -1095,17 +1095,6 @@ bool ActivityAnalyzer::isConstantValue(TypeResults const &TR, Value *Val) {
   // infinite loop
   if (auto ce = dyn_cast<ConstantExpr>(Val)) {
     if (ce->isCast()) {
-      if (auto PT = dyn_cast<PointerType>(ce->getType())) {
-        if (PT->getPointerElementType()->isFunctionTy()) {
-          if (EnzymePrintActivity)
-            llvm::errs()
-                << " VALUE nonconst as cast to pointer of functiontype " << *Val
-                << "\n";
-          ActiveValues.insert(Val);
-          return false;
-        }
-      }
-
       if (isConstantValue(TR, ce->getOperand(0))) {
         if (EnzymePrintActivity)
           llvm::errs() << " VALUE const cast from from operand " << *Val

enzyme/test/Enzyme/ReverseMode/invcglobal.ll

@@ -0,0 +1,39 @@
+; RUN: %opt < %s %loadEnzyme -enzyme -enzyme-preopt=false -mem2reg -instsimplify -simplifycfg -S | FileCheck %s
+
+@g = constant i8* null, align 8
+
+define void @_Z3barv(void ()** %i2) {
+  store void ()* bitcast (i8** @g to void ()*), void ()** %i2, align 8
+  ret void
+}
+
+define double @_Z3fooRd(double* nocapture readonly %arg) {
+  %ai2 = alloca void ()*, align 8
+  call void @_Z3barv(void ()** %ai2)
+  %a8 = load void ()*, void ()** %ai2, align 8
+  ret double 0.000000e+00
+}
+
+define void @caller(double* %i, double* %i2) {
+  %i6 = call double (...) @__enzyme_autodiff(i8* bitcast (double (double*)* @_Z3fooRd to i8*), double* %i, double* %i2)
+  ret void
+}
+
+declare double @__enzyme_autodiff(...)
+
+; CHECK: define internal void @diffe_Z3fooRd(double* nocapture readonly %arg, double* nocapture %"arg'", double %differeturn)
+; CHECK-NEXT: invert:
+; CHECK-NEXT:   %"ai2'ipa" = alloca void ()*, align 8
+; CHECK-NEXT:   store void ()* null, void ()** %"ai2'ipa", align 8
+; CHECK-NEXT:   %ai2 = alloca void ()*, align 8
+; CHECK-NEXT:   call void @diffe_Z3barv(void ()** %ai2, void ()** %"ai2'ipa")
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: }
+
+; CHECK: define internal void @diffe_Z3barv(void ()** %i2, void ()** %"i2'")
+; CHECK-NEXT: invert:
+; CHECK-NEXT:   store void ()* bitcast (i8** @g to void ()*), void ()** %"i2'", align 8
+; CHECK-NEXT:   store void ()* bitcast (i8** @g to void ()*), void ()** %i2, align 8
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: }
+