Fix call segfault (rust-lang#821)

Author: wsmoses

enzyme/Enzyme/AdjointGenerator.h

@@ -11832,6 +11832,9 @@ class AdjointGenerator
                               orig->getName() + "'ac");
             assert(newip->getType() == orig->getType());
             placeholder->replaceAllUsesWith(newip);
+            if (placeholder == &*BuilderZ.GetInsertPoint()) {
+              BuilderZ.SetInsertPoint(placeholder->getNextNode());
+            }
             gutils->erase(placeholder);
           } else {
             newip = placeholder;

enzyme/Enzyme/GradientUtils.cpp

@@ -2166,8 +2166,13 @@ Value *GradientUtils::cacheForReverse(IRBuilder<> &BuilderQ, Value *malloc,
       if (!ignoreType && replace)
         cast<Instruction>(malloc)->replaceAllUsesWith(ret);
       ret->takeName(malloc);
-      if (replace)
-        erase(cast<Instruction>(malloc));
+      if (replace) {
+        auto malloci = cast<Instruction>(malloc);
+        if (malloci == &*BuilderQ.GetInsertPoint()) {
+          BuilderQ.SetInsertPoint(malloci->getNextNode());
+        }
+        erase(malloci);
+      }
     }
     return ret;
   } else {

enzyme/test/Enzyme/ReverseMode/callseg.ll

@@ -0,0 +1,28 @@
+; RUN: %opt < %s %loadEnzyme -enzyme -enzyme-preopt=false -mem2reg -simplifycfg -S | FileCheck %s
+
+declare i8* @_Znwm(i64 %s)
+
+define void @ifunc(i8* %arg) {
+bb:
+  %i66 = call i8* @recur(i8* %arg)
+  ret void
+}
+
+define i8* @recur(i8* %arg) {
+bb: 
+  %i = call i8* @_Znwm(i64 8)
+  %i20 = call i8* @recur(i8* %i)
+  %i24 = bitcast i8* %arg to i8**
+  store i8* %i20, i8** %i24, align 8
+  ret i8* %i
+}
+
+declare void @_Z17__enzyme_autodiff(...) 
+
+define void @caller(i8* %a, i8* %b) {
+  tail call void (...) @_Z17__enzyme_autodiff(void (i8*)* @ifunc, metadata !"enzyme_dup", i8* %a, i8* %b)
+  ret void
+}
+
+; Ensure this compiles without segfaulting
+; CHECK: define internal void @differecur(i8* %arg, i8* %"arg'")