Fix gep memset error (#1876)

enzyme/Enzyme/AdjointGenerator.h

@@ -3262,7 +3262,7 @@ class AdjointGenerator : public llvm::InstVisitor<AdjointGenerator> {
           if (start != 0) {
             Value *idxs[] = {
                 ConstantInt::get(Type::getInt32Ty(op0->getContext()), start)};
-            op0 = BuilderZ.CreateInBoundsGEP(Type::getInt8Ty(op0->getContext()),
+            op0 = Builder2.CreateInBoundsGEP(Type::getInt8Ty(op0->getContext()),
                                              op0, idxs);
           }
           SmallVector<Value *, 4> args = {op0, op1l, length};

enzyme/test/Enzyme/ReverseMode/memset-intfloat2.ll

@@ -0,0 +1,38 @@
+; RUN: if [ %llvmver -lt 16 ]; then %opt < %s %loadEnzyme -enzyme -enzyme-preopt=false -mem2reg -simplifycfg -S | FileCheck %s; fi
+; RUN: %opt < %s %newLoadEnzyme -enzyme-preopt=false -passes="enzyme,function(mem2reg,%simplifycfg)" -S | FileCheck %s
+
+declare void @__enzyme_autodiff(...)
+
+declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1)
+
+declare void @g()
+
+define void @f(i8* %x, i1 %c) {
+  br i1 %c, label %t, label %exit
+
+t:
+  call void @llvm.memset.p0i8.i64(i8* %x, i8 0, i64 16, i1 false)
+  %xp = bitcast i8* %x to double*
+  %flt = load double, double* %xp, align 8, !tbaa !4
+  %g = getelementptr inbounds double, double* %xp, i32 1
+  %int = load double, double* %g, align 8, !tbaa !7
+  br label %exit
+
+exit:
+  call void @g() "enzyme_inactive"
+  ret void
+}
+
+define void @df(double* %x, double* %xp) {
+  tail call void (...) @__enzyme_autodiff(i8* bitcast (void (i8*, i1)* @f to i8*), metadata !"enzyme_dup", double* %x, double* %xp, i1 true)
+  ret void
+}
+
+!4 = !{!"long", !5, i64 0}
+!7 = !{!"double", !5, i64 0}
+!5 = !{!"omnipotent char", !6, i64 0}
+!6 = !{!"Simple C++ TBAA"}
+
+; CHECK:  %1 = getelementptr inbounds i8, i8* %"x'", i32 8
+; CHECK-NEXT:  call void @llvm.memset.p0i8.i64(i8* %1, i8 0, i64 8, i1 false)
+