[flang-commits] [flang] [flang] Implement conditional expressions lowering (F2023) (PR #186490)

[Caroline Newcombe via flang-commits]

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@@ -1821,6 +1821,196 @@ class HlfirBuilder {
     llvm_unreachable("unknown descriptor inquiry");
   }
 
+  /// Build nested if-then-else chain by walking the right-skewed
+  /// ConditionalExpr tree. The assignValue callback generates and assigns
+  /// each value to avoid evaluating non-taken branches.
+  template <typename T, typename Callback>
+  void
+  buildConditionalIfChain(const Fortran::evaluate::ConditionalExpr<T> &condExpr,
+                          const Callback &assignValue) {
+    const mlir::Location loc{getLoc()};
+    fir::FirOpBuilder &builder{getBuilder()};
+    getStmtCtx().pushScope();
+    const hlfir::EntityWithAttributes condEntity{gen(condExpr.condition())};
+    mlir::Value condition{hlfir::loadTrivialScalar(loc, builder, condEntity)};
+    condition = builder.createConvert(loc, builder.getI1Type(), condition);
+    builder.genIfOp(loc, {}, condition, /*withElseRegion=*/true)
+        .genThen([&]() {
+          getStmtCtx().pushScope();
+          assignValue(condExpr.thenValue());
+          getStmtCtx().finalizeAndPop();
+        })
+        .genElse([&]() {
+          // Recurse for nested ConditionalExpr; else assign terminal value.
+          if (const auto *nested =
+                  std::get_if<Fortran::evaluate::ConditionalExpr<T>>(
+                      &condExpr.elseValue().u)) {
+            buildConditionalIfChain(*nested, assignValue);
+          } else {
+            getStmtCtx().pushScope();
+            assignValue(condExpr.elseValue());
+            getStmtCtx().finalizeAndPop();
+          }
+        })
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cenewcombe wrote:

I think it makes the most sense to simplify here, done ✅ 

https://github.com/llvm/llvm-project/pull/186490