[flang][fir]: Add conversion of `fir.if` to `scf.if`. #149959

terapines-osc-mlir · 2025-07-22T04:14:39Z

This commmit is a supplement for #140374.
RFC:https://discourse.llvm.org/t/rfc-add-fir-affine-optimization-fir-pass-pipeline/86190/6

github-actions · 2025-07-22T04:14:56Z

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llvmbot · 2025-07-22T04:15:28Z

@llvm/pr-subscribers-flang-fir-hlfir

Author: Terapines MLIR (terapines-osc-mlir)

Changes

This commmit is a supplement for #140374.
RFC:https://discourse.llvm.org/t/rfc-add-fir-affine-optimization-fir-pass-pipeline/86190/6

Full diff: https://github.com/llvm/llvm-project/pull/149959.diff

2 Files Affected:

(modified) flang/lib/Optimizer/Transforms/FIRToSCF.cpp (+48-2)
(added) flang/test/Fir/FirToSCF/if.fir (+57)

diff --git a/flang/lib/Optimizer/Transforms/FIRToSCF.cpp b/flang/lib/Optimizer/Transforms/FIRToSCF.cpp
index d7d1865bc56ba..ad9d8ec136b22 100644
--- a/flang/lib/Optimizer/Transforms/FIRToSCF.cpp
+++ b/flang/lib/Optimizer/Transforms/FIRToSCF.cpp
@@ -87,13 +87,59 @@ struct DoLoopConversion : public OpRewritePattern<fir::DoLoopOp> {
     return success();
   }
 };
+
+void copyBlocksAndTransformResult(PatternRewriter &rewriter, Block &srcBlock,
+                                  Block &dstBlock) {
+  Operation *srcTerminator = srcBlock.getTerminator();
+  auto resultOp = dyn_cast<fir::ResultOp>(srcTerminator);
+
+  /// Do a simple copy when fir.result is not used.
+  if (resultOp == nullptr) {
+    dstBlock.getOperations().splice(dstBlock.begin(), srcBlock.getOperations());
+    return;
+  }
+
+  /// Drop the fir.result and insert a scf.yield in the end of the block
+  dstBlock.getOperations().splice(dstBlock.begin(), srcBlock.getOperations(),
+                                  srcBlock.begin(), std::prev(srcBlock.end()));
+
+  if (!resultOp->getOperands().empty()) {
+    rewriter.setInsertionPointToEnd(&dstBlock);
+    rewriter.create<scf::YieldOp>(resultOp.getLoc(), resultOp.getOperands());
+  }
+
+  rewriter.eraseOp(srcTerminator);
+}
+
+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();
+    bool hasElse = !ifOp.getElseRegion().empty();
+    auto scfIfOp = rewriter.create<scf::IfOp>(loc, ifOp->getResultTypes(),
+                                              ifOp.getCondition(), hasElse);
+
+    copyBlocksAndTransformResult(rewriter, ifOp.getThenRegion().front(),
+                                 scfIfOp.getThenRegion().front());
+
+    if (hasElse) {
+      copyBlocksAndTransformResult(rewriter, ifOp.getElseRegion().front(),
+                                   scfIfOp.getElseRegion().front());
+    }
+
+    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))))
diff --git a/flang/test/Fir/FirToSCF/if.fir b/flang/test/Fir/FirToSCF/if.fir
new file mode 100644
index 0000000000000..fbb2f179411cf
--- /dev/null
+++ b/flang/test/Fir/FirToSCF/if.fir
@@ -0,0 +1,57 @@
+// RUN: fir-opt %s --fir-to-scf | FileCheck %s
+
+// CHECK-LABEL:   func.func @test_only(
+// CHECK-SAME:      %[[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-LABEL:   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
+}
\ No newline at end of file

tblah

LGTM thanks!

tblah · 2025-07-22T11:06:46Z

flang/lib/Optimizer/Transforms/FIRToSCF.cpp

+
+  if (!resultOp->getOperands().empty()) {
+    rewriter.setInsertionPointToEnd(&dstBlock);
+    rewriter.create<scf::YieldOp>(resultOp.getLoc(), resultOp.getOperands());


Note that this old syntax is being replaced with YieldOp::create(rewriter, ....). For example, see #149917

Thanks! All rewriter.create<T>(...)s are replaced by T::create(rewriter, ...)s.

rscottmanley · 2025-07-22T12:59:06Z

flang/lib/Optimizer/Transforms/FIRToSCF.cpp

@@ -87,13 +87,52 @@ struct DoLoopConversion : public OpRewritePattern<fir::DoLoopOp> {
    return success();
  }
 };
+
+void copyBlocksAndTransformResult(PatternRewriter &rewriter, Block &srcBlock,


I think this should be a lambda instead

I think this should be a lambda instead

Copying block and transforming terminator is a common operation which can be shared by other functions in this file. Since all Fir to SCF transforms will be written in this file, I would like to keep this function this way for now.

rscottmanley · 2025-07-22T13:00:15Z

The title of this MR confused me for a minute, can it just be "add conversion of fir.if to scf.if"? or "convert fir.if in FIRToSCF"

terapines-osc-mlir · 2025-07-23T02:50:54Z

The title of this MR confused me for a minute, can it just be "add conversion of fir.if to scf.if"? or "convert fir.if in FIRToSCF"

Thanks! Commit message is changed to what you had suggested.

github-actions · 2025-07-25T02:04:08Z

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This commmit is a supplement for llvm#140374. RFC:https://discourse.llvm.org/t/rfc-add-fir-affine-optimization-fir-pass-pipeline/86190/6

llvmbot added flang Flang issues not falling into any other category flang:fir-hlfir labels Jul 22, 2025

NexMing requested review from kiranchandramohan and NexMing July 22, 2025 05:12

terapines-osc-mlir force-pushed the firif-to-scfif branch 2 times, most recently from 358ac2c to 9ef83e5 Compare July 22, 2025 05:43

NexMing approved these changes Jul 22, 2025

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clementval requested a review from rscottmanley July 22, 2025 05:46

terapines-osc-mlir force-pushed the firif-to-scfif branch 2 times, most recently from 77baecd to de4de9c Compare July 22, 2025 08:47

tblah approved these changes Jul 22, 2025

View reviewed changes

tblah reviewed Jul 22, 2025

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rscottmanley reviewed Jul 22, 2025

View reviewed changes

terapines-osc-mlir force-pushed the firif-to-scfif branch 2 times, most recently from 3f548d1 to 0b0eef6 Compare July 23, 2025 02:35

[flang][fir]: Add conversion of fir.if to scf.if.

3e73c00

terapines-osc-mlir force-pushed the firif-to-scfif branch from 0b0eef6 to 3e73c00 Compare July 23, 2025 02:49

NexMing changed the title ~~[flang][fir]: New optimizer transform of fir.if to scf.if.~~ [flang][fir]: Add conversion of fir.if to scf.if. Jul 23, 2025

NexMing changed the title ~~[flang][fir]: Add conversion of fir.if to scf.if.~~ [flang][fir]: Add conversion of fir.if to scf.if. Jul 23, 2025

terapines-osc-mlir requested a review from rscottmanley July 24, 2025 02:03

NexMing merged commit 8e9ca05 into llvm:main Jul 25, 2025
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[flang][fir]: Add conversion of fir.if to scf.if. #149959

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[flang][fir]: Add conversion of `fir.if` to `scf.if`. #149959

[flang][fir]: Add conversion of `fir.if` to `scf.if`. #149959