Better sret (rust-lang#708)

Author: wsmoses

enzyme/Enzyme/Enzyme.cpp

@@ -1254,14 +1254,19 @@ class Enzyme : public ModulePass {
 #endif
           CI->replaceAllUsesWith(cload);
         } else {
-          llvm::errs() << *CI << " - " << *diffret << "\n";
-          assert(0 && " what");
+          EmitFailure("IllegalReturnCast", CI->getDebugLoc(), CI,
+                      "Cannot cast return type of gradient ",
+                      *diffret->getType(), *diffret, ", to desired type ",
+                      *CI->getType());
+          return false;
         }
       } else if (CI->hasStructRetAttr()) {
         Value *sret = CI->getArgOperand(0);
+        PointerType *stype = cast<PointerType>(sret->getType());
+        StructType *st = dyn_cast<StructType>(stype->getElementType());
 
         // Assign results to struct allocated at the call site.
-        if (StructType *st = cast<StructType>(diffret->getType())) {
+        if (st && st->isLayoutIdentical(diffretsty)) {
           for (unsigned int i = 0; i < st->getNumElements(); i++) {
 #if LLVM_VERSION_MAJOR > 7
             Value *sgep = Builder.CreateStructGEP(
@@ -1271,6 +1276,20 @@ class Enzyme : public ModulePass {
 #endif
             Builder.CreateStore(Builder.CreateExtractValue(diffret, {i}), sgep);
           }
+        } else {
+          auto &DL = fn->getParent()->getDataLayout();
+          if (DL.getTypeSizeInBits(stype->getElementType()) !=
+              DL.getTypeSizeInBits(diffret->getType())) {
+            EmitFailure("IllegalReturnCast", CI->getDebugLoc(), CI,
+                        "Cannot cast return type of gradient ",
+                        *diffret->getType(), *diffret, ", to desired type ",
+                        *stype->getElementType());
+            return false;
+          }
+          Builder.CreateStore(
+              diffret, Builder.CreatePointerCast(
+                           sret, PointerType::get(diffret->getType(),
+                                                  stype->getAddressSpace())));
         }
       } else {
 

enzyme/test/Integration/ReverseMode/sret.cpp

@@ -0,0 +1,38 @@
+// RUN: %clang++ -std=c++11 -fno-exceptions -ffast-math -O0 %s -S -emit-llvm -o - | %opt - %loadEnzyme -enzyme -S
+// RUN: %clang++ -std=c++11 -fno-exceptions -ffast-math -O1 %s -S -emit-llvm -o - | %opt - %loadEnzyme -enzyme -S
+// RUN: %clang++ -std=c++11 -fno-exceptions -ffast-math -O2 %s -S -emit-llvm -o - | %opt - %loadEnzyme -enzyme -S
+// RUN: %clang++ -std=c++11 -fno-exceptions -ffast-math -O3 %s -S -emit-llvm -o - | %opt - %loadEnzyme -enzyme -S
+// RUN: %clang++ -std=c++11 -fno-exceptions -ffast-math -O0 %s -S -emit-llvm -o - | %opt - %loadEnzyme -enzyme -enzyme-inline=1 -S
+// RUN: %clang++ -std=c++11 -fno-exceptions -ffast-math -O1 %s -S -emit-llvm -o - | %opt - %loadEnzyme -enzyme -enzyme-inline=1 -S
+// RUN: %clang++ -std=c++11 -fno-exceptions -ffast-math -O2 %s -S -emit-llvm -o - | %opt - %loadEnzyme -enzyme -enzyme-inline=1 -S
+// RUN: %clang++ -std=c++11 -fno-exceptions -ffast-math -O3 %s -S -emit-llvm -o - | %opt - %loadEnzyme -enzyme -enzyme-inline=1 -S
+
+#include "test_utils.h"
+#include <iostream>
+#include <sstream>
+#include <utility>
+
+typedef struct {
+    double df[3];
+} Gradient;
+extern Gradient __enzyme_autodiff(void*, double, double , double);
+
+double myfunction(double x, double y, double z){
+    return x * y * z;
+}
+
+void dmyfunction(double x, double y, double z, double* res) {
+    Gradient g = __enzyme_autodiff((void*)myfunction, x, y, z);
+
+    res[0]=g.df[0];
+    res[1]=g.df[1];
+    res[2]=g.df[2];
+}
+
+int main() {
+    double *res=new double(3);
+    dmyfunction(3,4,5,res);
+    APPROX_EQ(res[0], 4*5., 1e-7);
+    APPROX_EQ(res[1], 3*5., 1e-7);
+    APPROX_EQ(res[1], 3*4., 1e-7);
+}