added helper function

Author: gitoleg

clang/lib/CIR/CodeGen/CIRGenCall.cpp

@@ -551,6 +551,18 @@ static cir::CIRCallOpInterface emitCallLikeOp(
                               extraFnAttrs);
 }
 
+static RValue getRValueThroughMemory(mlir::Location loc, 
+                                     CIRGenBuilderTy &builder,  
+                                     mlir::Value val, 
+                                     Address addr) {
+  auto ip = builder.saveInsertionPoint();
+  builder.setInsertionPointAfterValue(val);
+  builder.createStore(loc, val, addr);
+  builder.restoreInsertionPoint(ip);
+  auto load = builder.createLoad(loc, addr);
+  return RValue::get(load);
+}
+
 RValue CIRGenFunction::emitCall(const CIRGenFunctionInfo &CallInfo,
                                 const CIRGenCallee &Callee,
                                 ReturnValueSlot ReturnValue,
@@ -890,19 +902,14 @@ RValue CIRGenFunction::emitCall(const CIRGenFunctionInfo &CallInfo,
           assert(Results.size() <= 1 && "multiple returns NYI");
           assert(Results[0].getType() == RetCIRTy && "Bitcast support NYI");
 
-          auto reg = builder.getBlock()->getParent();
-          if (reg != theCall->getParentRegion()) {
+          auto region = builder.getBlock()->getParent();
+          if (region != theCall->getParentRegion()) {
             Address DestPtr = ReturnValue.getValue();
 
             if (!DestPtr.isValid())
               DestPtr = CreateMemTemp(RetTy, callLoc, "tmp");
 
-            auto ip = builder.saveInsertionPoint();
-            builder.setInsertionPointAfter(theCall);
-            builder.createStore(callLoc, Results[0], DestPtr);
-            builder.restoreInsertionPoint(ip);
-            auto load = builder.createLoad(callLoc, DestPtr);
-            return RValue::get(load);
+            return getRValueThroughMemory(callLoc, builder, Results[0], DestPtr);
           }
 
           return RValue::get(Results[0]);

clang/lib/CIR/Dialect/Transforms/FlattenCFG.cpp

@@ -19,6 +19,8 @@
 #include "clang/CIR/Dialect/IR/CIRDialect.h"
 #include "clang/CIR/Dialect/Passes.h"
 
+#include <iostream>
+
 using namespace mlir;
 using namespace cir;
 
@@ -910,6 +912,42 @@ void populateFlattenCFGPatterns(RewritePatternSet &patterns) {
           patterns.getContext());
 }
 
+void removeTempAllocas(DominanceInfo& dom, FuncOp fun) {
+
+  fun.walk([&](AllocaOp op) {
+    if (op.getName().str().find("tmp") == std::string::npos)
+      return;
+
+    StoreOp store;
+    LoadOp load;
+    int total = 0;    
+
+    for (auto* u : op->getUsers()) {      
+      total++;
+      if (auto ld = dyn_cast<LoadOp>(u))
+        load = ld;
+      if (auto st = dyn_cast<StoreOp>(u))
+        if (st.getAddr() == op.getResult())
+          store = st;
+    }
+
+    if (total == 2 && load && store && dom.dominates(store, load)) {
+      if (load->hasOneUse()) {
+        if (auto st = dyn_cast<StoreOp>(*load->user_begin())) {
+          if (auto al = dyn_cast<AllocaOp>(st.getAddr().getDefiningOp())) {
+            llvm::SmallVector<mlir::Value> vals;
+            vals.push_back(al.getResult());
+            op->replaceAllUsesWith(vals);
+            op->erase();
+          }
+        }
+      }
+    }
+    
+  });
+
+}
+
 void FlattenCFGPass::runOnOperation() {
   RewritePatternSet patterns(&getContext());
   populateFlattenCFGPatterns(patterns);
@@ -924,6 +962,12 @@ void FlattenCFGPass::runOnOperation() {
   // Apply patterns.
   if (applyOpPatternsAndFold(ops, std::move(patterns)).failed())
     signalPassFailure();
+
+  auto &dom = getAnalysis<DominanceInfo>();
+  
+  getOperation()->walk([&](FuncOp fun) {
+    removeTempAllocas(dom, fun);
+  });  
 }
 
 } // namespace