Add inactive global specifier (rust-lang#938)

* Add inactive global

* Add custom inactive global specification

Author: wsmoses

enzyme/Enzyme/ActivityAnalysis.cpp

@@ -1092,6 +1092,10 @@ bool ActivityAnalyzer::isConstantValue(TypeResults const &TR, Value *Val) {
       InsertConstantValue(TR, Val);
       return true;
     }
+    if (hasMetadata(GI, "enzyme_inactive")) {
+      InsertConstantValue(TR, Val);
+      return true;
+    }
 
     if (GI->getName().contains("enzyme_const") ||
         InactiveGlobals.count(GI->getName().str())) {
@@ -2571,6 +2575,9 @@ bool ActivityAnalyzer::isValueInactiveFromUsers(TypeResults const &TR,
                   EnzymeNonmarkedGlobalsInactive) {
                 continue;
               }
+              if (hasMetadata(GV, "enzyme_inactive")) {
+                continue;
+              }
               if (GV->getName().contains("enzyme_const") ||
                   InactiveGlobals.count(GV->getName().str())) {
                 continue;

enzyme/Enzyme/PreserveNVVM.cpp

@@ -150,6 +150,32 @@ class PreserveNVVM final : public FunctionPass {
         }
       }
     }
+    SmallVector<GlobalVariable *, 1> toErase;
+    for (GlobalVariable &g : F.getParent()->globals()) {
+      if (g.getName().contains("__enzyme_inactive_global")) {
+        if (g.hasInitializer()) {
+          Value *V = g.getInitializer();
+          while (1) {
+            if (auto CE = dyn_cast<ConstantExpr>(V)) {
+              V = CE->getOperand(0);
+              continue;
+            }
+            if (auto CA = dyn_cast<ConstantAggregate>(V)) {
+              V = CA->getOperand(0);
+              continue;
+            }
+            break;
+          }
+          if (auto GV = cast<GlobalVariable>(V)) {
+            GV->setMetadata("enzyme_inactive", MDNode::get(g.getContext(), {}));
+            toErase.push_back(&g);
+          }
+        }
+      }
+    }
+    for (auto G : toErase)
+      G->eraseFromParent();
+
     if (!Begin && F.hasFnAttribute("prev_fixup")) {
       changed = true;
       F.removeFnAttr("prev_fixup");

enzyme/test/Integration/ReverseMode/customglob.cpp

@@ -0,0 +1,37 @@
+// RUN: if [ %llvmver -ge 12 ]; then %clang++ -O0 %s -S -emit-llvm -o - %loadClangEnzyme | %lli - ; fi
+// RUN: if [ %llvmver -ge 12 ]; then %clang++ -O1 %s -S -emit-llvm -o - %loadClangEnzyme | %lli - ; fi
+// RUN: if [ %llvmver -ge 12 ]; then %clang++ -O2 %s -S -emit-llvm -o - %loadClangEnzyme | %lli - ; fi
+// RUN: if [ %llvmver -ge 12 ]; then %clang++ -O3 %s -S -emit-llvm -o - %loadClangEnzyme | %lli - ; fi
+// RUN: if [ %llvmver -ge 12 ]; then %clang++ -O0 %s -S -emit-llvm -o - %loadClangEnzyme -mllvm -enzyme-inline=1 -S | %lli - ; fi
+// RUN: if [ %llvmver -ge 12 ]; then %clang++ -O1 %s -S -emit-llvm -o - %loadClangEnzyme -mllvm -enzyme-inline=1 -S | %lli - ; fi
+// RUN: if [ %llvmver -ge 12 ]; then %clang++ -O2 %s -S -emit-llvm -o - %loadClangEnzyme -mllvm -enzyme-inline=1 -S | %lli - ; fi
+// RUN: if [ %llvmver -ge 12 ]; then %clang++ -O3 %s -S -emit-llvm -o - %loadClangEnzyme -mllvm -enzyme-inline=1 -S | %lli - ; fi
+
+#include "test_utils.h"
+
+double __enzyme_autodiff(void*, ...);
+
+enum class MyMemoryType
+{
+   DEFAULT
+};
+
+extern MyMemoryType host_mem_type;
+
+__attribute__((noinline))
+void* alloc(int size, MyMemoryType mt) {
+    return malloc(size);
+}
+
+double square(double a)
+{
+  double* D = (double*)alloc(sizeof(double), host_mem_type);
+  D[0] = a;
+  return D[0];
+}
+void* __enzyme_inactive_global = &host_mem_type;
+
+int main() {
+  double out = __enzyme_autodiff((void*)square, 10.0);
+  APPROX_EQ(out, 1.0, 1e-7);
+}