[flang][fir] Add fir.if -> scf.if and add filecheck test file (#142965)

This commmit is a supplement for
#140374.

RFC:https://discourse.llvm.org/t/rfc-add-fir-affine-optimization-fir-pass-pipeline/86190/6

---------

Co-authored-by: ZhiQiang Fan <[email protected]>

Author: StarryCSF

flang/lib/Optimizer/Transforms/FIRToSCF.cpp

@@ -87,13 +87,48 @@ struct DoLoopConversion : public OpRewritePattern<fir::DoLoopOp> {
     return success();
   }
 };
+
+struct IfConversion : public OpRewritePattern<fir::IfOp> {
+  using OpRewritePattern<fir::IfOp>::OpRewritePattern;
+  LogicalResult matchAndRewrite(fir::IfOp ifOp,
+                                PatternRewriter &rewriter) const override {
+    mlir::Location loc = ifOp.getLoc();
+    mlir::detail::TypedValue<mlir::IntegerType> condition = ifOp.getCondition();
+    ValueTypeRange<ResultRange> resultTypes = ifOp.getResultTypes();
+    mlir::scf::IfOp scfIfOp = rewriter.create<scf::IfOp>(
+        loc, resultTypes, condition, !ifOp.getElseRegion().empty());
+    // then region
+    scfIfOp.getThenRegion().takeBody(ifOp.getThenRegion());
+    Block &scfThenBlock = scfIfOp.getThenRegion().front();
+    Operation *scfThenTerminator = scfThenBlock.getTerminator();
+    // fir.result->scf.yield
+    rewriter.setInsertionPointToEnd(&scfThenBlock);
+    rewriter.replaceOpWithNewOp<scf::YieldOp>(scfThenTerminator,
+                                              scfThenTerminator->getOperands());
+
+    // else region
+    if (!ifOp.getElseRegion().empty()) {
+      scfIfOp.getElseRegion().takeBody(ifOp.getElseRegion());
+      mlir::Block &elseBlock = scfIfOp.getElseRegion().front();
+      mlir::Operation *elseTerminator = elseBlock.getTerminator();
+
+      rewriter.setInsertionPointToEnd(&elseBlock);
+      rewriter.replaceOpWithNewOp<scf::YieldOp>(elseTerminator,
+                                                elseTerminator->getOperands());
+    }
+
+    scfIfOp->setAttrs(ifOp->getAttrs());
+    rewriter.replaceOp(ifOp, scfIfOp);
+    return success();
+  }
+};
 } // namespace
 
 void FIRToSCFPass::runOnOperation() {
   RewritePatternSet patterns(&getContext());
-  patterns.add<DoLoopConversion>(patterns.getContext());
+  patterns.add<DoLoopConversion, IfConversion>(patterns.getContext());
   ConversionTarget target(getContext());
-  target.addIllegalOp<fir::DoLoopOp>();
+  target.addIllegalOp<fir::DoLoopOp, fir::IfOp>();
   target.markUnknownOpDynamicallyLegal([](Operation *) { return true; });
   if (failed(
           applyPartialConversion(getOperation(), target, std::move(patterns))))

flang/test/Fir/FirToSCF/if.fir

@@ -0,0 +1,56 @@
+// RUN: fir-opt %s --fir-to-scf | FileCheck %s
+
+// CHECK: func.func @test_only(%[[ARG0:.*]]: i1, %[[ARG1:.*]]: i32) {
+// CHECK:   scf.if %[[ARG0:.*]] {
+// CHECK:    %[[VAL_1:.*]] = arith.addi %[[ARG1:.*]], %[[ARG1:.*]] : i32
+// CHECK:   }
+// CHECK:   return
+// CHECK:   }
+func.func @test_only(%arg0 : i1, %arg1 : i32) {
+  fir.if %arg0 {
+    %0 = arith.addi %arg1, %arg1 : i32
+  }
+  return
+}
+
+// CHECK: func.func @test_else()   {
+// CHECK:   %[[VAL_1:.*]] = arith.constant false
+// CHECK:   %[[VAL_2:.*]] = arith.constant 2 : i32
+// CHECK:   scf.if %[[VAL_1:.*]] {
+// CHECK:     %[[VAL_3:.*]] = arith.constant 3 : i32
+// CHECK:   } else {
+// CHECK:     %[[VAL_3:.*]] = arith.constant 3 : i32
+// CHECK:   }
+// CHECK:   return
+// CHECK: }
+func.func @test_else()   {
+  %false = arith.constant false
+  %1 = arith.constant 2 : i32
+  fir.if %false {
+    %2 = arith.constant 3 : i32
+  } else {
+    %3 = arith.constant 3 : i32
+  }
+  return
+}
+
+// CHECK-LABEL:     func.func @test_two_result()  {
+// CHECK:           %[[VAL_1:.*]] = arith.constant 2.000000e+00 : f32
+// CHECK:           %[[VAL_2:.*]] = arith.constant false
+// CHECK:           %[[RES:[0-9]+]]:2 = scf.if %[[VAL_2:.*]] -> (f32, f32) {
+// CHECK:            scf.yield %[[VAL_1:.*]], %[[VAL_1:.*]] : f32, f32
+// CHECK:            } else {
+// CHECK:              scf.yield %[[VAL_1:.*]], %[[VAL_1:.*]] : f32, f32
+// CHECK:            }
+// CHECK:            return 
+// CHECK:            }
+func.func @test_two_result() {
+  %1 = arith.constant 2.0 : f32
+  %cmp = arith.constant false
+  %x, %y = fir.if %cmp -> (f32, f32) {
+    fir.result %1, %1 : f32, f32
+  } else {
+    fir.result %1, %1 : f32, f32
+  }
+  return
+}