diff --git a/enzyme/CMakeLists.txt b/enzyme/CMakeLists.txt
index 80f0dc95481a..af3e6c7c9157 100644
--- a/enzyme/CMakeLists.txt
+++ b/enzyme/CMakeLists.txt
@@ -58,10 +58,14 @@ if (NOT DEFINED LLVM_EXTERNAL_LIT)
       message("found llvm match ${CMAKE_MATCH_1} dir ${LLVM_DIR}")
     if (EXISTS ${LLVM_DIR}/../../../bin/llvm-lit) 
       set(LLVM_EXTERNAL_LIT ${LLVM_DIR}/../../../bin/llvm-lit) 
+    else()
+      set(LLVM_EXTERNAL_LIT lit)
     endif()
   else()
     if (EXISTS ${LLVM_DIR}/bin/llvm-lit) 
       set(LLVM_EXTERNAL_LIT ${LLVM_DIR}/bin/llvm-lit) 
+    else()
+      set(LLVM_EXTERNAL_LIT lit)
     endif()
   endif()
 endif()
diff --git a/enzyme/Enzyme/AdjointGenerator.h b/enzyme/Enzyme/AdjointGenerator.h
index 7660e012b84f..5cd84f0c250c 100644
--- a/enzyme/Enzyme/AdjointGenerator.h
+++ b/enzyme/Enzyme/AdjointGenerator.h
@@ -935,12 +935,25 @@ class AdjointGenerator
   }
 
   void visitAtomicRMWInst(llvm::AtomicRMWInst &I) {
-    if (Mode == DerivativeMode::ForwardMode) {
-      IRBuilder<> BuilderZ(&I);
-      getForwardBuilder(BuilderZ);
-      switch (I.getOperation()) {
-      case AtomicRMWInst::FAdd:
-      case AtomicRMWInst::FSub: {
+
+    if (gutils->isConstantInstruction(&I) && gutils->isConstantValue(&I)) {
+      if (Mode == DerivativeMode::ReverseModeGradient ||
+          Mode == DerivativeMode::ForwardModeSplit) {
+        eraseIfUnused(I, /*erase*/ true, /*check*/ false);
+      } else {
+        eraseIfUnused(I);
+      }
+      return;
+    }
+
+    switch (I.getOperation()) {
+    case AtomicRMWInst::FAdd:
+    case AtomicRMWInst::FSub: {
+
+      if (Mode == DerivativeMode::ForwardMode ||
+          Mode == DerivativeMode::ForwardModeSplit) {
+        IRBuilder<> BuilderZ(&I);
+        getForwardBuilder(BuilderZ);
         auto rule = [&](Value *ptr, Value *dif) -> Value * {
           if (!gutils->isConstantInstruction(&I)) {
             assert(ptr);
@@ -981,32 +994,84 @@ class AdjointGenerator
           setDiffe(&I, diff, BuilderZ);
         return;
       }
-      default:
-        break;
+      if (Mode == DerivativeMode::ReverseModePrimal) {
+        eraseIfUnused(I);
+        return;
       }
-    }
-    if (!gutils->isConstantInstruction(&I) || !gutils->isConstantValue(&I)) {
-      if (looseTypeAnalysis) {
-        auto &DL = gutils->newFunc->getParent()->getDataLayout();
-        auto valType = I.getValOperand()->getType();
-        auto storeSize = DL.getTypeSizeInBits(valType) / 8;
-        auto fp = TR.firstPointer(storeSize, I.getPointerOperand(),
-                                  /*errifnotfound*/ false,
-                                  /*pointerIntSame*/ true);
-        if (!fp.isKnown() && valType->isIntOrIntVectorTy()) {
-          goto noerror;
+      if ((Mode == DerivativeMode::ReverseModeCombined ||
+           Mode == DerivativeMode::ReverseModeGradient) &&
+          gutils->isConstantValue(&I)) {
+        if (!gutils->isConstantValue(I.getValOperand())) {
+          assert(!gutils->isConstantValue(I.getPointerOperand()));
+          IRBuilder<> Builder2(&I);
+          getReverseBuilder(Builder2);
+          Value *ip = gutils->invertPointerM(I.getPointerOperand(), Builder2);
+          auto order = I.getOrdering();
+          if (order == AtomicOrdering::Release)
+            order = AtomicOrdering::Monotonic;
+          else if (order == AtomicOrdering::AcquireRelease)
+            order = AtomicOrdering::Acquire;
+
+          auto rule = [&](Value *ip) -> Value * {
+#if LLVM_VERSION_MAJOR > 7
+            LoadInst *dif1 =
+                Builder2.CreateLoad(I.getType(), ip, I.isVolatile());
+#else
+            LoadInst *dif1 = Builder2.CreateLoad(ip, I.isVolatile());
+#endif
+
+#if LLVM_VERSION_MAJOR >= 11
+            dif1->setAlignment(I.getAlign());
+#else
+            const DataLayout &DL = I.getModule()->getDataLayout();
+            auto tmpAlign = DL.getTypeStoreSize(I.getValOperand()->getType());
+#if LLVM_VERSION_MAJOR >= 10
+            dif1->setAlignment(MaybeAlign(tmpAlign.getFixedSize()));
+#else
+            dif1->setAlignment(tmpAlign);
+#endif
+#endif
+            dif1->setOrdering(order);
+            dif1->setSyncScopeID(I.getSyncScopeID());
+            return dif1;
+          };
+          Value *diff = applyChainRule(I.getType(), Builder2, rule, ip);
+
+          addToDiffe(I.getValOperand(), diff, Builder2,
+                     I.getValOperand()->getType()->getScalarType());
         }
+        if (Mode == DerivativeMode::ReverseModeGradient) {
+          eraseIfUnused(I, /*erase*/ true, /*check*/ false);
+        } else
+          eraseIfUnused(I);
+        return;
       }
-      TR.dump();
-      llvm::errs() << "oldFunc: " << *gutils->newFunc << "\n";
-      llvm::errs() << "I: " << I << "\n";
-      assert(0 && "Active atomic inst not handled");
+      break;
+    }
+    default:
+      break;
     }
-  noerror:;
 
-    if (Mode == DerivativeMode::ReverseModeGradient) {
-      eraseIfUnused(I, /*erase*/ true, /*check*/ false);
+    if (looseTypeAnalysis) {
+      auto &DL = gutils->newFunc->getParent()->getDataLayout();
+      auto valType = I.getValOperand()->getType();
+      auto storeSize = DL.getTypeSizeInBits(valType) / 8;
+      auto fp = TR.firstPointer(storeSize, I.getPointerOperand(),
+                                /*errifnotfound*/ false,
+                                /*pointerIntSame*/ true);
+      if (!fp.isKnown() && valType->isIntOrIntVectorTy()) {
+        if (Mode == DerivativeMode::ReverseModeGradient ||
+            Mode == DerivativeMode::ReverseModeGradient) {
+          eraseIfUnused(I, /*erase*/ true, /*check*/ false);
+        } else
+          eraseIfUnused(I);
+        return;
+      }
     }
+    TR.dump();
+    llvm::errs() << "oldFunc: " << *gutils->newFunc << "\n";
+    llvm::errs() << "I: " << I << "\n";
+    llvm_unreachable("Active atomic inst not yet handled");
   }
 
   void visitStoreInst(llvm::StoreInst &SI) {
diff --git a/enzyme/test/Enzyme/ReverseMode/atomicfadd.ll b/enzyme/test/Enzyme/ReverseMode/atomicfadd.ll
new file mode 100644
index 000000000000..d254608f6130
--- /dev/null
+++ b/enzyme/test/Enzyme/ReverseMode/atomicfadd.ll
@@ -0,0 +1,90 @@
+; RUN: if [ %llvmver -ge 9 ]; then %opt < %s %loadEnzyme -enzyme -enzyme-preopt=false -mem2reg -sroa -instsimplify -simplifycfg -S | FileCheck %s; fi
+
+; ModuleID = '<source>'
+source_filename = "<source>"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define dso_local void @foo1(double* %p, double %v) {
+  %a10 = atomicrmw volatile fadd double* %p, double %v monotonic
+  ret void
+}
+define dso_local void @foo2(double* %p, double %v) {
+  %a10 = atomicrmw volatile fadd double* %p, double %v acquire
+  ret void
+}
+define dso_local void @foo3(double* %p, double %v) {
+  %a10 = atomicrmw volatile fadd double* %p, double %v release
+  ret void
+}
+define dso_local void @foo4(double* %p, double %v) {
+  %a10 = atomicrmw volatile fadd double* %p, double %v acq_rel
+  ret void
+}
+define dso_local void @foo5(double* %p, double %v) {
+  %a10 = atomicrmw volatile fadd double* %p, double %v seq_cst
+  ret void
+}
+define dso_local void @foo6(double* %p, double %v) {
+  %a10 = atomicrmw volatile fadd double* %p, double 1.000000e+00 seq_cst
+  ret void
+}
+
+define void @caller(double* %a, double* %b, double %v) {
+  %r1 = call double @_Z17__enzyme_autodiffPviRdS0_(i8* bitcast (void (double*, double)* @foo1 to i8*), double* %a, double* %b, double %v)
+  %r2 = call double @_Z17__enzyme_autodiffPviRdS0_(i8* bitcast (void (double*, double)* @foo2 to i8*), double* %a, double* %b, double %v)
+  %r3 = call double @_Z17__enzyme_autodiffPviRdS0_(i8* bitcast (void (double*, double)* @foo3 to i8*), double* %a, double* %b, double %v)
+  %r4 = call double @_Z17__enzyme_autodiffPviRdS0_(i8* bitcast (void (double*, double)* @foo4 to i8*), double* %a, double* %b, double %v)
+  %r5 = call double @_Z17__enzyme_autodiffPviRdS0_(i8* bitcast (void (double*, double)* @foo5 to i8*), double* %a, double* %b, double %v)
+  %r6 = call double @_Z17__enzyme_autodiffPviRdS0_(i8* bitcast (void (double*, double)* @foo6 to i8*), double* %a, double* %b, double %v)
+  ret void
+}
+
+declare double @_Z17__enzyme_autodiffPviRdS0_(i8*, double*, double*, double)
+
+
+; CHECK: define internal { double } @diffefoo1(double* %p, double* %"p'", double %v)
+; CHECK-NEXT: invert:
+; CHECK-NEXT:   %a10 = atomicrmw volatile fadd double* %p, double %v monotonic
+; CHECK-NEXT:   %0 = load atomic volatile double, double* %"p'" monotonic, align 8
+; CHECK-NEXT:   %1 = insertvalue { double } {{(undef|poison)}}, double %0, 0
+; CHECK-NEXT:   ret { double } %1
+; CHECK-NEXT: }
+
+; CHECK: define internal { double } @diffefoo2(double* %p, double* %"p'", double %v)
+; CHECK-NEXT: invert:
+; CHECK-NEXT:   %a10 = atomicrmw volatile fadd double* %p, double %v acquire
+; CHECK-NEXT:   %0 = load atomic volatile double, double* %"p'" acquire, align 8
+; CHECK-NEXT:   %1 = insertvalue { double } {{(undef|poison)}}, double %0, 0
+; CHECK-NEXT:   ret { double } %1
+; CHECK-NEXT: }
+
+; CHECK: define internal { double } @diffefoo3(double* %p, double* %"p'", double %v)
+; CHECK-NEXT: invert:
+; CHECK-NEXT:   %a10 = atomicrmw volatile fadd double* %p, double %v release
+; CHECK-NEXT:   %0 = load atomic volatile double, double* %"p'" monotonic, align 8
+; CHECK-NEXT:   %1 = insertvalue { double } {{(undef|poison)}}, double %0, 0
+; CHECK-NEXT:   ret { double } %1
+; CHECK-NEXT: }
+
+; CHECK: define internal { double } @diffefoo4(double* %p, double* %"p'", double %v)
+; CHECK-NEXT: invert:
+; CHECK-NEXT:   %a10 = atomicrmw volatile fadd double* %p, double %v acq_rel
+; CHECK-NEXT:   %0 = load atomic volatile double, double* %"p'" acquire, align 8
+; CHECK-NEXT:   %1 = insertvalue { double } {{(undef|poison)}}, double %0, 0
+; CHECK-NEXT:   ret { double } %1
+; CHECK-NEXT: }
+
+; CHECK: define internal { double } @diffefoo5(double* %p, double* %"p'", double %v)
+; CHECK-NEXT: invert:
+; CHECK-NEXT:   %a10 = atomicrmw volatile fadd double* %p, double %v seq_cst
+; CHECK-NEXT:   %0 = load atomic volatile double, double* %"p'" seq_cst, align 8
+; CHECK-NEXT:   %1 = insertvalue { double } {{(undef|poison)}}, double %0, 0
+; CHECK-NEXT:   ret { double } %1
+; CHECK-NEXT: }
+
+; CHECK: define internal { double } @diffefoo6(double* %p, double* %"p'", double %v)
+; CHECK-NEXT: invert:
+; CHECK-NEXT:   %a10 = atomicrmw volatile fadd double* %p, double 1.000000e+00 seq_cst
+; CHECK-NEXT:   ret { double } zeroinitializer
+; CHECK-NEXT: }
diff --git a/enzyme/test/Enzyme/ReverseModeVector/atomicadd.ll b/enzyme/test/Enzyme/ReverseModeVector/atomicadd.ll
new file mode 100644
index 000000000000..122dbe6770e5
--- /dev/null
+++ b/enzyme/test/Enzyme/ReverseModeVector/atomicadd.ll
@@ -0,0 +1,42 @@
+; RUN: if [ %llvmver -ge 9 ]; then %opt < %s %loadEnzyme -enzyme -enzyme-preopt=false -mem2reg -sroa -instsimplify -simplifycfg -S | FileCheck %s; fi
+
+; ModuleID = '<source>'
+source_filename = "<source>"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define dso_local void @foo1(double* %p, double %v) {
+  %a10 = atomicrmw volatile fadd double* %p, double %v monotonic
+  ret void
+}
+define dso_local void @foo6(double* %p, double %v) {
+  %a10 = atomicrmw volatile fadd double* %p, double 1.000000e+00 seq_cst
+  ret void
+}
+
+define void @caller(double* %a, double* %b, double %v) {
+  %r1 = call [2 x double] (...) @_Z17__enzyme_autodiffPviRdS0_(i8* bitcast (void (double*, double)* @foo1 to i8*), metadata !"enzyme_width", i64 2, double* %a, double* %b, double* %b, double %v)
+  %r6 = call [2 x double] (...) @_Z17__enzyme_autodiffPviRdS0_(i8* bitcast (void (double*, double)* @foo6 to i8*), metadata !"enzyme_width", i64 2, double* %a, double* %b, double* %b, double %v)
+  ret void
+}
+
+declare [2 x double] @_Z17__enzyme_autodiffPviRdS0_(...)
+
+; CHECK: define internal { [2 x double] } @diffe2foo1(double* %p, [2 x double*] %"p'", double %v)
+; CHECK-NEXT: invert:
+; CHECK-NEXT:   %a10 = atomicrmw volatile fadd double* %p, double %v monotonic
+; CHECK-NEXT:   %0 = extractvalue [2 x double*] %"p'", 0
+; CHECK-NEXT:   %1 = load atomic volatile double, double* %0 monotonic, align 8
+; CHECK-NEXT:   %2 = extractvalue [2 x double*] %"p'", 1
+; CHECK-NEXT:   %3 = load atomic volatile double, double* %2 monotonic, align 8
+; CHECK-NEXT:   %.fca.0.insert5 = insertvalue [2 x double] {{(undef|poison)}}, double %1, 0
+; CHECK-NEXT:   %.fca.1.insert8 = insertvalue [2 x double] %.fca.0.insert5, double %3, 1
+; CHECK-NEXT:   %4 = insertvalue { [2 x double] } undef, [2 x double] %.fca.1.insert8, 0
+; CHECK-NEXT:   ret { [2 x double] } %4
+; CHECK-NEXT: }
+
+; CHECK: define internal { [2 x double] } @diffe2foo6(double* %p, [2 x double*] %"p'", double %v)
+; CHECK-NEXT: invert:
+; CHECK-NEXT:   %a10 = atomicrmw volatile fadd double* %p, double 1.000000e+00 seq_cst
+; CHECK-NEXT:   ret { [2 x double] } zeroinitializer
+; CHECK-NEXT: }
\ No newline at end of file