ForwardMode: extractelement inst (rust-lang#353)

Author: tgymnich

enzyme/Enzyme/AdjointGenerator.h

@@ -1140,26 +1140,51 @@ class AdjointGenerator
     if (Mode == DerivativeMode::ReverseModePrimal)
       return;
 
-    IRBuilder<> Builder2(EEI.getParent());
-    getReverseBuilder(Builder2);
+    switch (Mode) {
+    case DerivativeMode::ForwardMode: {
+      IRBuilder<> Builder2(&EEI);
+      getForwardBuilder(Builder2);
 
-    Value *orig_vec = EEI.getVectorOperand();
+      Value *orig_vec = EEI.getVectorOperand();
 
-    if (!gutils->isConstantValue(orig_vec)) {
-      SmallVector<Value *, 4> sv;
-      sv.push_back(gutils->getNewFromOriginal(EEI.getIndexOperand()));
+      auto vec_diffe = gutils->isConstantValue(orig_vec)
+                           ? ConstantVector::getNullValue(orig_vec->getType())
+                           : diffe(orig_vec, Builder2);
+      auto diffe =
+          Builder2.CreateExtractElement(vec_diffe, EEI.getIndexOperand());
 
-      size_t size = 1;
-      if (EEI.getType()->isSized())
-        size = (gutils->newFunc->getParent()->getDataLayout().getTypeSizeInBits(
-                    EEI.getType()) +
-                7) /
-               8;
-      ((DiffeGradientUtils *)gutils)
-          ->addToDiffe(orig_vec, diffe(&EEI, Builder2), Builder2,
-                       TR.addingType(size, &EEI), sv);
+      setDiffe(&EEI, diffe, Builder2);
+      return;
+    }
+    case DerivativeMode::ReverseModeGradient:
+    case DerivativeMode::ReverseModeCombined: {
+      IRBuilder<> Builder2(EEI.getParent());
+      getReverseBuilder(Builder2);
+
+      Value *orig_vec = EEI.getVectorOperand();
+
+      if (!gutils->isConstantValue(orig_vec)) {
+        SmallVector<Value *, 4> sv;
+        sv.push_back(gutils->getNewFromOriginal(EEI.getIndexOperand()));
+
+        size_t size = 1;
+        if (EEI.getType()->isSized())
+          size =
+              (gutils->newFunc->getParent()->getDataLayout().getTypeSizeInBits(
+                   EEI.getType()) +
+               7) /
+              8;
+        ((DiffeGradientUtils *)gutils)
+            ->addToDiffe(orig_vec, diffe(&EEI, Builder2), Builder2,
+                         TR.addingType(size, &EEI), sv);
+      }
+      setDiffe(&EEI, Constant::getNullValue(EEI.getType()), Builder2);
+      return;
+    }
+    case DerivativeMode::ReverseModePrimal: {
+      return;
+    }
     }
-    setDiffe(&EEI, Constant::getNullValue(EEI.getType()), Builder2);
   }
 
   void visitInsertElementInst(llvm::InsertElementInst &IEI) {