[Mlir-commits] [mlir] 3ada774 - Revert "Add a structured if operation (#67234)"

Gil Rapaport llvmlistbot at llvm.org
Wed Sep 27 14:30:15 PDT 2023


Author: Gil Rapaport
Date: 2023-09-28T00:22:42+03:00
New Revision: 3ada774d0f65b44f21b360d222f446e533df1a34

URL: https://github.com/llvm/llvm-project/commit/3ada774d0f65b44f21b360d222f446e533df1a34
DIFF: https://github.com/llvm/llvm-project/commit/3ada774d0f65b44f21b360d222f446e533df1a34.diff

LOG: Revert "Add a structured if operation (#67234)"

This reverts commit 126f0374cbc2110aa97e2141ac898014a8b9531a.

Reverting due to bot failures.

Added: 
    

Modified: 
    mlir/docs/Dialects/emitc.md
    mlir/include/mlir/Conversion/Passes.h
    mlir/include/mlir/Conversion/Passes.td
    mlir/include/mlir/Dialect/EmitC/IR/EmitC.h
    mlir/include/mlir/Dialect/EmitC/IR/EmitC.td
    mlir/lib/Conversion/CMakeLists.txt
    mlir/lib/Dialect/EmitC/IR/EmitC.cpp
    mlir/lib/Target/Cpp/TranslateToCpp.cpp
    mlir/test/Dialect/EmitC/invalid_ops.mlir
    mlir/test/Dialect/EmitC/ops.mlir
    mlir/test/Target/Cpp/if.mlir

Removed: 
    mlir/include/mlir/Conversion/SCFToEmitC/SCFToEmitC.h
    mlir/lib/Conversion/SCFToEmitC/CMakeLists.txt
    mlir/lib/Conversion/SCFToEmitC/SCFToEmitC.cpp
    mlir/test/Conversion/SCFToEmitC/if.mlir


################################################################################
diff  --git a/mlir/docs/Dialects/emitc.md b/mlir/docs/Dialects/emitc.md
index 4d9f04ab11c8f0c..995cf06e1b39c0f 100644
--- a/mlir/docs/Dialects/emitc.md
+++ b/mlir/docs/Dialects/emitc.md
@@ -33,6 +33,7 @@ translating the following operations:
     *   `func.return`
 *   'scf' Dialect
     *   `scf.for`
+    *   `scf.if`
     *   `scf.yield`
 *   'arith' Dialect
     *   `arith.constant`

diff  --git a/mlir/include/mlir/Conversion/Passes.h b/mlir/include/mlir/Conversion/Passes.h
index 41806004fc1dca8..fc5e9adba114405 100644
--- a/mlir/include/mlir/Conversion/Passes.h
+++ b/mlir/include/mlir/Conversion/Passes.h
@@ -48,7 +48,6 @@
 #include "mlir/Conversion/PDLToPDLInterp/PDLToPDLInterp.h"
 #include "mlir/Conversion/ReconcileUnrealizedCasts/ReconcileUnrealizedCasts.h"
 #include "mlir/Conversion/SCFToControlFlow/SCFToControlFlow.h"
-#include "mlir/Conversion/SCFToEmitC/SCFToEmitC.h"
 #include "mlir/Conversion/SCFToGPU/SCFToGPUPass.h"
 #include "mlir/Conversion/SCFToOpenMP/SCFToOpenMP.h"
 #include "mlir/Conversion/SCFToSPIRV/SCFToSPIRVPass.h"

diff  --git a/mlir/include/mlir/Conversion/Passes.td b/mlir/include/mlir/Conversion/Passes.td
index 9b7848d9288be43..5e0f976b18f7da5 100644
--- a/mlir/include/mlir/Conversion/Passes.td
+++ b/mlir/include/mlir/Conversion/Passes.td
@@ -931,16 +931,6 @@ def ConvertParallelLoopToGpu : Pass<"convert-parallel-loops-to-gpu"> {
   let dependentDialects = ["affine::AffineDialect", "gpu::GPUDialect"];
 }
 
-//===----------------------------------------------------------------------===//
-// SCFToEmitC
-//===----------------------------------------------------------------------===//
-
-def SCFToEmitC : Pass<"convert-scf-to-emitc"> {
-  let summary = "Convert SCF dialect to EmitC dialect, maintaining structured"
-                " control flow";
-  let dependentDialects = ["emitc::EmitCDialect"];
-}
-
 //===----------------------------------------------------------------------===//
 // ShapeToStandard
 //===----------------------------------------------------------------------===//

diff  --git a/mlir/include/mlir/Conversion/SCFToEmitC/SCFToEmitC.h b/mlir/include/mlir/Conversion/SCFToEmitC/SCFToEmitC.h
deleted file mode 100644
index 4fe405ed1d3a987..000000000000000
--- a/mlir/include/mlir/Conversion/SCFToEmitC/SCFToEmitC.h
+++ /dev/null
@@ -1,29 +0,0 @@
-//===- SCFToEmitC.h - SCF to EmitC Pass entrypoint --------------*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef MLIR_CONVERSION_SCFTOEMITC_SCFTOEMITC_H_
-#define MLIR_CONVERSION_SCFTOEMITC_SCFTOEMITC_H_
-
-#include <memory>
-
-namespace mlir {
-class Pass;
-class RewritePatternSet;
-
-#define GEN_PASS_DECL_SCFTOEMITC
-#include "mlir/Conversion/Passes.h.inc"
-
-/// Collect a set of patterns to convert SCF operations to the EmitC dialect.
-void populateSCFToEmitCConversionPatterns(RewritePatternSet &patterns);
-
-/// Creates a pass to convert SCF operations to the EmitC dialect.
-std::unique_ptr<Pass> createConvertSCFToEmitCPass();
-
-} // namespace mlir
-
-#endif // MLIR_CONVERSION_SCFTOEMITC_SCFTOEMITC_H_

diff  --git a/mlir/include/mlir/Dialect/EmitC/IR/EmitC.h b/mlir/include/mlir/Dialect/EmitC/IR/EmitC.h
index 4dff26e23c42850..b3c1170eefdab90 100644
--- a/mlir/include/mlir/Dialect/EmitC/IR/EmitC.h
+++ b/mlir/include/mlir/Dialect/EmitC/IR/EmitC.h
@@ -14,23 +14,15 @@
 #define MLIR_DIALECT_EMITC_IR_EMITC_H
 
 #include "mlir/Bytecode/BytecodeOpInterface.h"
-#include "mlir/IR/Builders.h"
 #include "mlir/IR/BuiltinOps.h"
 #include "mlir/IR/BuiltinTypes.h"
 #include "mlir/IR/Dialect.h"
 #include "mlir/Interfaces/CastInterfaces.h"
-#include "mlir/Interfaces/ControlFlowInterfaces.h"
 #include "mlir/Interfaces/SideEffectInterfaces.h"
 
 #include "mlir/Dialect/EmitC/IR/EmitCDialect.h.inc"
 #include "mlir/Dialect/EmitC/IR/EmitCEnums.h.inc"
 
-namespace mlir {
-namespace emitc {
-void buildTerminatedBody(OpBuilder &builder, Location loc);
-} // namespace emitc
-} // namespace mlir
-
 #define GET_ATTRDEF_CLASSES
 #include "mlir/Dialect/EmitC/IR/EmitCAttributes.h.inc"
 

diff  --git a/mlir/include/mlir/Dialect/EmitC/IR/EmitC.td b/mlir/include/mlir/Dialect/EmitC/IR/EmitC.td
index 827ffc0278fce1c..40a4896aca4b633 100644
--- a/mlir/include/mlir/Dialect/EmitC/IR/EmitC.td
+++ b/mlir/include/mlir/Dialect/EmitC/IR/EmitC.td
@@ -17,7 +17,6 @@ include "mlir/Dialect/EmitC/IR/EmitCAttributes.td"
 include "mlir/Dialect/EmitC/IR/EmitCTypes.td"
 
 include "mlir/Interfaces/CastInterfaces.td"
-include "mlir/Interfaces/ControlFlowInterfaces.td"
 include "mlir/Interfaces/SideEffectInterfaces.td"
 
 //===----------------------------------------------------------------------===//
@@ -403,102 +402,4 @@ def EmitC_VariableOp : EmitC_Op<"variable", []> {
   let hasVerifier = 1;
 }
 
-def EmitC_AssignOp : EmitC_Op<"assign", []> {
-  let summary = "Assign operation";
-  let description = [{
-    The `assign` operation stores an SSA value to the location designated by an
-    EmitC variable. This operation doesn't return any value. The assigned value
-    must be of the same type as the variable being assigned. The operation is
-    emitted as a C/C++ '=' operator.
-
-    Example:
-
-    ```mlir
-    // Integer variable
-    %0 = "emitc.variable"(){value = 42 : i32} : () -> i32
-    %1 = emitc.call "foo"() : () -> (i32)
-
-    // Assign emitted as `... = ...;`
-    "emitc.assign"(%0, %1) : (i32, i32) -> ()
-    ```
-  }];
-
-  let arguments = (ins AnyType:$var, AnyType:$value);
-  let results = (outs);
-
-  let hasVerifier = 1;
-  let assemblyFormat = "$value `:` type($value) `to` $var `:` type($var) attr-dict";
-}
-
-def EmitC_YieldOp : EmitC_Op<"yield", [Pure, Terminator, ParentOneOf<["IfOp"]>]> {
-  let summary = "block termination operation";
-  let description = [{
-    "yield" terminates blocks within EmitC control-flow operations. Since
-    control-flow constructs in C do not return values, this operation doesn't
-    take any arguments.
-  }];
-
-  let arguments = (ins);
-  let builders = [OpBuilder<(ins), [{ /* nothing to do */ }]>];
-
-  let assemblyFormat = [{ attr-dict }];
-}
-
-def EmitC_IfOp : EmitC_Op<"if",
-    [DeclareOpInterfaceMethods<RegionBranchOpInterface, [
-    "getNumRegionInvocations", "getRegionInvocationBounds",
-    "getEntrySuccessorRegions"]>, SingleBlock,
-    SingleBlockImplicitTerminator<"emitc::YieldOp">,
-    RecursiveMemoryEffects, NoRegionArguments]> {
-  let summary = "if-then-else operation";
-  let description = [{
-    The `if` operation represents an if-then-else construct for
-    conditionally executing two regions of code. The operand to an if operation
-    is a boolean value. For example:
-
-    ```mlir
-    emitc.if %b  {
-      ...
-    } else {
-      ...
-    }
-    ```
-
-    The "then" region has exactly 1 block. The "else" region may have 0 or 1
-    blocks. The blocks are always terminated with `emitc.yield`, which can be
-    left out to be inserted implicitly. This operation doesn't produce any
-    results.
-  }];
-  let arguments = (ins I1:$condition);
-  let results = (outs);
-  let regions = (region SizedRegion<1>:$thenRegion,
-                        MaxSizedRegion<1>:$elseRegion);
-
-  let skipDefaultBuilders = 1;
-  let builders = [
-    OpBuilder<(ins "Value":$cond)>,
-    OpBuilder<(ins "Value":$cond, "bool":$addThenBlock, "bool":$addElseBlock)>,
-    OpBuilder<(ins "Value":$cond, "bool":$withElseRegion)>,
-    OpBuilder<(ins "Value":$cond,
-      CArg<"function_ref<void(OpBuilder &, Location)>",
-           "buildTerminatedBody">:$thenBuilder,
-      CArg<"function_ref<void(OpBuilder &, Location)>",
-           "nullptr">:$elseBuilder)>,
-  ];
-
-  let extraClassDeclaration = [{
-    OpBuilder getThenBodyBuilder(OpBuilder::Listener *listener = nullptr) {
-      Block* body = getBody(0);
-      return OpBuilder::atBlockEnd(body, listener);
-    }
-    OpBuilder getElseBodyBuilder(OpBuilder::Listener *listener = nullptr) {
-      Block* body = getBody(1);
-      return OpBuilder::atBlockEnd(body, listener);
-    }
-    Block* thenBlock();
-    Block* elseBlock();
-  }];
-  let hasCustomAssemblyFormat = 1;
-}
-
 #endif // MLIR_DIALECT_EMITC_IR_EMITC

diff  --git a/mlir/lib/Conversion/CMakeLists.txt b/mlir/lib/Conversion/CMakeLists.txt
index 660e48768c4ff34..275e095245e89ce 100644
--- a/mlir/lib/Conversion/CMakeLists.txt
+++ b/mlir/lib/Conversion/CMakeLists.txt
@@ -38,7 +38,6 @@ add_subdirectory(OpenMPToLLVM)
 add_subdirectory(PDLToPDLInterp)
 add_subdirectory(ReconcileUnrealizedCasts)
 add_subdirectory(SCFToControlFlow)
-add_subdirectory(SCFToEmitC)
 add_subdirectory(SCFToGPU)
 add_subdirectory(SCFToOpenMP)
 add_subdirectory(SCFToSPIRV)

diff  --git a/mlir/lib/Conversion/SCFToEmitC/CMakeLists.txt b/mlir/lib/Conversion/SCFToEmitC/CMakeLists.txt
deleted file mode 100644
index 79119d374f7a5e9..000000000000000
--- a/mlir/lib/Conversion/SCFToEmitC/CMakeLists.txt
+++ /dev/null
@@ -1,18 +0,0 @@
-add_mlir_conversion_library(MLIRSCFToEmitC
-  SCFToEmitC.cpp
-
-  ADDITIONAL_HEADER_DIRS
-  ${MLIR_MAIN_INCLUDE_DIR}/mlir/Conversion/SCFToEmitC
-
-  DEPENDS
-  MLIRConversionPassIncGen
-
-  LINK_COMPONENTS
-  Core
-
-  LINK_LIBS PUBLIC
-  MLIRArithDialect
-  MLIREmitCDialect
-  MLIRSCFDialect
-  MLIRTransforms
-  )

diff  --git a/mlir/lib/Conversion/SCFToEmitC/SCFToEmitC.cpp b/mlir/lib/Conversion/SCFToEmitC/SCFToEmitC.cpp
deleted file mode 100644
index 5d0d8df8869e313..000000000000000
--- a/mlir/lib/Conversion/SCFToEmitC/SCFToEmitC.cpp
+++ /dev/null
@@ -1,130 +0,0 @@
-//===- SCFToEmitC.cpp - SCF to EmitC conversion ---------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-//
-// This file implements a pass to convert scf.if ops into emitc ops.
-//
-//===----------------------------------------------------------------------===//
-
-#include "mlir/Conversion/SCFToEmitC/SCFToEmitC.h"
-
-#include "mlir/Dialect/Arith/IR/Arith.h"
-#include "mlir/Dialect/EmitC/IR/EmitC.h"
-#include "mlir/Dialect/SCF/IR/SCF.h"
-#include "mlir/IR/Builders.h"
-#include "mlir/IR/BuiltinOps.h"
-#include "mlir/IR/IRMapping.h"
-#include "mlir/IR/MLIRContext.h"
-#include "mlir/IR/PatternMatch.h"
-#include "mlir/Transforms/DialectConversion.h"
-#include "mlir/Transforms/Passes.h"
-
-namespace mlir {
-#define GEN_PASS_DEF_SCFTOEMITC
-#include "mlir/Conversion/Passes.h.inc"
-} // namespace mlir
-
-using namespace mlir;
-using namespace mlir::scf;
-
-namespace {
-
-struct SCFToEmitCPass : public impl::SCFToEmitCBase<SCFToEmitCPass> {
-  void runOnOperation() override;
-};
-
-// Lower scf::if to emitc::if, implementing return values as emitc::variable's
-// updated within the then and else regions.
-struct IfLowering : public OpRewritePattern<IfOp> {
-  using OpRewritePattern<IfOp>::OpRewritePattern;
-
-  LogicalResult matchAndRewrite(IfOp ifOp,
-                                PatternRewriter &rewriter) const override;
-};
-
-} // namespace
-
-LogicalResult IfLowering::matchAndRewrite(IfOp ifOp,
-                                          PatternRewriter &rewriter) const {
-  Location loc = ifOp.getLoc();
-
-  SmallVector<Value> resultVariables;
-
-  // Create an emitc::variable op for each result. These variables will be
-  // assigned to by emitc::assign ops within the then & else regions.
-  if (ifOp.getNumResults()) {
-    MLIRContext *context = ifOp.getContext();
-    rewriter.setInsertionPoint(ifOp);
-    for (OpResult result : ifOp.getResults()) {
-      Type resultType = result.getType();
-      auto noInit = emitc::OpaqueAttr::get(context, "");
-      auto var = rewriter.create<emitc::VariableOp>(loc, resultType, noInit);
-      resultVariables.push_back(var);
-    }
-  }
-
-  // Utility function to lower the contents of an scf::if region to an emitc::if
-  // region. The contents of the scf::if regions is moved into the respective
-  // emitc::if regions, but the scf::yield is replaced not only with an
-  // emitc::yield, but also with a sequence of emitc::assign ops that set the
-  // yielded values into the result variables.
-  auto lowerRegion = [&resultVariables, &rewriter](Region &region,
-                                                   Region &loweredRegion) {
-    rewriter.inlineRegionBefore(region, loweredRegion, loweredRegion.end());
-    Operation *terminator = loweredRegion.back().getTerminator();
-    Location terminatorLoc = terminator->getLoc();
-    ValueRange terminatorOperands = terminator->getOperands();
-    rewriter.setInsertionPointToEnd(&loweredRegion.back());
-    for (auto value2Var : llvm::zip(terminatorOperands, resultVariables)) {
-      Value resultValue = std::get<0>(value2Var);
-      Value resultVar = std::get<1>(value2Var);
-      rewriter.create<emitc::AssignOp>(terminatorLoc, resultVar, resultValue);
-    }
-    rewriter.create<emitc::YieldOp>(terminatorLoc);
-    rewriter.eraseOp(terminator);
-  };
-
-  Region &thenRegion = ifOp.getThenRegion();
-  Region &elseRegion = ifOp.getElseRegion();
-
-  bool hasElseBlock = !elseRegion.empty();
-
-  auto loweredIf =
-      rewriter.create<emitc::IfOp>(loc, ifOp.getCondition(), false, false);
-
-  Region &loweredThenRegion = loweredIf.getThenRegion();
-  lowerRegion(thenRegion, loweredThenRegion);
-
-  if (hasElseBlock) {
-    Region &loweredElseRegion = loweredIf.getElseRegion();
-    lowerRegion(elseRegion, loweredElseRegion);
-  }
-
-  rewriter.replaceOp(ifOp, resultVariables);
-  return success();
-}
-
-void mlir::populateSCFToEmitCConversionPatterns(RewritePatternSet &patterns) {
-  patterns.add<IfLowering>(patterns.getContext());
-}
-
-void SCFToEmitCPass::runOnOperation() {
-  RewritePatternSet patterns(&getContext());
-  populateSCFToEmitCConversionPatterns(patterns);
-
-  // Configure conversion to lower out SCF operations.
-  ConversionTarget target(getContext());
-  target.addIllegalOp<scf::IfOp>();
-  target.markUnknownOpDynamicallyLegal([](Operation *) { return true; });
-  if (failed(
-          applyPartialConversion(getOperation(), target, std::move(patterns))))
-    signalPassFailure();
-}
-
-std::unique_ptr<Pass> mlir::createConvertSCFToEmitCPass() {
-  return std::make_unique<SCFToEmitCPass>();
-}

diff  --git a/mlir/lib/Dialect/EmitC/IR/EmitC.cpp b/mlir/lib/Dialect/EmitC/IR/EmitC.cpp
index 961a52a70a2a168..1c95ed07702d1db 100644
--- a/mlir/lib/Dialect/EmitC/IR/EmitC.cpp
+++ b/mlir/lib/Dialect/EmitC/IR/EmitC.cpp
@@ -44,12 +44,6 @@ Operation *EmitCDialect::materializeConstant(OpBuilder &builder,
   return builder.create<emitc::ConstantOp>(loc, type, value);
 }
 
-/// Default callback for builders of ops carrying a region. Inserts a yield
-/// without arguments.
-void mlir::emitc::buildTerminatedBody(OpBuilder &builder, Location loc) {
-  builder.create<emitc::YieldOp>(loc);
-}
-
 //===----------------------------------------------------------------------===//
 // AddOp
 //===----------------------------------------------------------------------===//
@@ -93,27 +87,6 @@ LogicalResult ApplyOp::verify() {
   return success();
 }
 
-//===----------------------------------------------------------------------===//
-// AssignOp
-//===----------------------------------------------------------------------===//
-
-/// The assign op requires that the assigned value's type matches the
-/// assigned-to variable type.
-LogicalResult emitc::AssignOp::verify() {
-  Value variable = getVar();
-  Operation *variableDef = variable.getDefiningOp();
-  if (!variableDef || !llvm::isa<emitc::VariableOp>(variableDef))
-    return emitOpError() << "requires first operand (" << variable
-                         << ") to be a Variable";
-
-  Value value = getValue();
-  if (variable.getType() != value.getType())
-    return emitOpError() << "requires value's type (" << value.getType()
-                         << ") to match variable's type (" << variable.getType()
-                         << ")";
-  return success();
-}
-
 //===----------------------------------------------------------------------===//
 // CastOp
 //===----------------------------------------------------------------------===//
@@ -189,166 +162,6 @@ LogicalResult emitc::ConstantOp::verify() {
 
 OpFoldResult emitc::ConstantOp::fold(FoldAdaptor adaptor) { return getValue(); }
 
-//===----------------------------------------------------------------------===//
-// IfOp
-//===----------------------------------------------------------------------===//
-
-void IfOp::build(OpBuilder &builder, OperationState &result, Value cond,
-                 bool addThenBlock, bool addElseBlock) {
-  assert((!addElseBlock || addThenBlock) &&
-         "must not create else block w/o then block");
-  result.addOperands(cond);
-
-  // Add regions and blocks.
-  OpBuilder::InsertionGuard guard(builder);
-  Region *thenRegion = result.addRegion();
-  if (addThenBlock)
-    builder.createBlock(thenRegion);
-  Region *elseRegion = result.addRegion();
-  if (addElseBlock)
-    builder.createBlock(elseRegion);
-}
-
-void IfOp::build(OpBuilder &builder, OperationState &result, Value cond,
-                 bool withElseRegion) {
-  result.addOperands(cond);
-
-  // Build then region.
-  OpBuilder::InsertionGuard guard(builder);
-  Region *thenRegion = result.addRegion();
-  builder.createBlock(thenRegion);
-
-  // Build else region.
-  Region *elseRegion = result.addRegion();
-  if (withElseRegion) {
-    builder.createBlock(elseRegion);
-  }
-}
-
-void IfOp::build(OpBuilder &builder, OperationState &result, Value cond,
-                 function_ref<void(OpBuilder &, Location)> thenBuilder,
-                 function_ref<void(OpBuilder &, Location)> elseBuilder) {
-  assert(thenBuilder && "the builder callback for 'then' must be present");
-  result.addOperands(cond);
-
-  // Build then region.
-  OpBuilder::InsertionGuard guard(builder);
-  Region *thenRegion = result.addRegion();
-  builder.createBlock(thenRegion);
-  thenBuilder(builder, result.location);
-
-  // Build else region.
-  Region *elseRegion = result.addRegion();
-  if (elseBuilder) {
-    builder.createBlock(elseRegion);
-    elseBuilder(builder, result.location);
-  }
-}
-
-ParseResult IfOp::parse(OpAsmParser &parser, OperationState &result) {
-  // Create the regions for 'then'.
-  result.regions.reserve(2);
-  Region *thenRegion = result.addRegion();
-  Region *elseRegion = result.addRegion();
-
-  Builder &builder = parser.getBuilder();
-  OpAsmParser::UnresolvedOperand cond;
-  Type i1Type = builder.getIntegerType(1);
-  if (parser.parseOperand(cond) ||
-      parser.resolveOperand(cond, i1Type, result.operands))
-    return failure();
-  // Parse the 'then' region.
-  if (parser.parseRegion(*thenRegion, /*arguments=*/{}, /*argTypes=*/{}))
-    return failure();
-  IfOp::ensureTerminator(*thenRegion, parser.getBuilder(), result.location);
-
-  // If we find an 'else' keyword then parse the 'else' region.
-  if (!parser.parseOptionalKeyword("else")) {
-    if (parser.parseRegion(*elseRegion, /*arguments=*/{}, /*argTypes=*/{}))
-      return failure();
-    IfOp::ensureTerminator(*elseRegion, parser.getBuilder(), result.location);
-  }
-
-  // Parse the optional attribute list.
-  if (parser.parseOptionalAttrDict(result.attributes))
-    return failure();
-  return success();
-}
-
-void IfOp::print(OpAsmPrinter &p) {
-  bool printBlockTerminators = false;
-
-  p << " " << getCondition();
-  p << ' ';
-  p.printRegion(getThenRegion(),
-                /*printEntryBlockArgs=*/false,
-                /*printBlockTerminators=*/printBlockTerminators);
-
-  // Print the 'else' regions if it exists and has a block.
-  Region &elseRegion = getElseRegion();
-  if (!elseRegion.empty()) {
-    p << " else ";
-    p.printRegion(elseRegion,
-                  /*printEntryBlockArgs=*/false,
-                  /*printBlockTerminators=*/printBlockTerminators);
-  }
-
-  p.printOptionalAttrDict((*this)->getAttrs());
-}
-
-/// Given the region at `index`, or the parent operation if `index` is None,
-/// return the successor regions. These are the regions that may be selected
-/// during the flow of control. `operands` is a set of optional attributes that
-/// correspond to a constant value for each operand, or null if that operand is
-/// not a constant.
-void IfOp::getSuccessorRegions(RegionBranchPoint point,
-                               SmallVectorImpl<RegionSuccessor> &regions) {
-  // The `then` and the `else` region branch back to the parent operation.
-  if (!point.isParent()) {
-    regions.push_back(RegionSuccessor());
-    return;
-  }
-
-  regions.push_back(RegionSuccessor(&getThenRegion()));
-
-  // Don't consider the else region if it is empty.
-  Region *elseRegion = &this->getElseRegion();
-  if (elseRegion->empty())
-    regions.push_back(RegionSuccessor());
-  else
-    regions.push_back(RegionSuccessor(elseRegion));
-}
-
-void IfOp::getEntrySuccessorRegions(ArrayRef<Attribute> operands,
-                                    SmallVectorImpl<RegionSuccessor> &regions) {
-  FoldAdaptor adaptor(operands, *this);
-  auto boolAttr = dyn_cast_or_null<BoolAttr>(adaptor.getCondition());
-  if (!boolAttr || boolAttr.getValue())
-    regions.emplace_back(&getThenRegion());
-
-  // If the else region is empty, execution continues after the parent op.
-  if (!boolAttr || !boolAttr.getValue()) {
-    if (!getElseRegion().empty())
-      regions.emplace_back(&getElseRegion());
-    else
-      regions.emplace_back();
-  }
-}
-
-void IfOp::getRegionInvocationBounds(
-    ArrayRef<Attribute> operands,
-    SmallVectorImpl<InvocationBounds> &invocationBounds) {
-  if (auto cond = llvm::dyn_cast_or_null<BoolAttr>(operands[0])) {
-    // If the condition is known, then one region is known to be executed once
-    // and the other zero times.
-    invocationBounds.emplace_back(0, cond.getValue() ? 1 : 0);
-    invocationBounds.emplace_back(0, cond.getValue() ? 0 : 1);
-  } else {
-    // Non-constant condition. Each region may be executed 0 or 1 times.
-    invocationBounds.assign(2, {0, 1});
-  }
-}
-
 //===----------------------------------------------------------------------===//
 // IncludeOp
 //===----------------------------------------------------------------------===//

diff  --git a/mlir/lib/Target/Cpp/TranslateToCpp.cpp b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
index 4645ca4b206e78c..832dd8f2013fa4d 100644
--- a/mlir/lib/Target/Cpp/TranslateToCpp.cpp
+++ b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
@@ -246,19 +246,6 @@ static LogicalResult printOperation(CppEmitter &emitter,
   return printConstantOp(emitter, operation, value);
 }
 
-static LogicalResult printOperation(CppEmitter &emitter,
-                                    emitc::AssignOp assignOp) {
-  auto variableOp = cast<emitc::VariableOp>(assignOp.getVar().getDefiningOp());
-  OpResult result = variableOp->getResult(0);
-
-  if (failed(emitter.emitVariableAssignment(result)))
-    return failure();
-
-  emitter.ostream() << emitter.getOrCreateName(assignOp.getValue());
-
-  return success();
-}
-
 static LogicalResult printBinaryOperation(CppEmitter &emitter,
                                           Operation *operation,
                                           StringRef binaryOperator) {
@@ -580,37 +567,45 @@ static LogicalResult printOperation(CppEmitter &emitter, scf::ForOp forOp) {
   return success();
 }
 
-static LogicalResult printOperation(CppEmitter &emitter, emitc::IfOp ifOp) {
+static LogicalResult printOperation(CppEmitter &emitter, scf::IfOp ifOp) {
   raw_indented_ostream &os = emitter.ostream();
 
-  // Helper function to emit all ops except the last one, expected to be
-  // emitc::yield.
-  auto emitAllExceptLast = [&emitter](Region &region) {
-    Region::OpIterator it = region.op_begin(), end = region.op_end();
-    for (; std::next(it) != end; ++it) {
-      if (failed(emitter.emitOperation(*it, /*trailingSemicolon=*/true)))
+  if (!emitter.shouldDeclareVariablesAtTop()) {
+    for (OpResult result : ifOp.getResults()) {
+      if (failed(emitter.emitVariableDeclaration(result,
+                                                 /*trailingSemicolon=*/true)))
         return failure();
     }
-    assert(isa<emitc::YieldOp>(*it) &&
-           "Expected last operation in the region to be emitc::yield");
-    return success();
-  };
+  }
 
   os << "if (";
   if (failed(emitter.emitOperands(*ifOp.getOperation())))
     return failure();
   os << ") {\n";
   os.indent();
-  if (failed(emitAllExceptLast(ifOp.getThenRegion())))
-    return failure();
+
+  Region &thenRegion = ifOp.getThenRegion();
+  for (Operation &op : thenRegion.getOps()) {
+    // Note: This prints a superfluous semicolon if the terminating yield op has
+    // zero results.
+    if (failed(emitter.emitOperation(op, /*trailingSemicolon=*/true)))
+      return failure();
+  }
+
   os.unindent() << "}";
 
   Region &elseRegion = ifOp.getElseRegion();
   if (!elseRegion.empty()) {
     os << " else {\n";
     os.indent();
-    if (failed(emitAllExceptLast(elseRegion)))
-      return failure();
+
+    for (Operation &op : elseRegion.getOps()) {
+      // Note: This prints a superfluous semicolon if the terminating yield op
+      // has zero results.
+      if (failed(emitter.emitOperation(op, /*trailingSemicolon=*/true)))
+        return failure();
+    }
+
     os.unindent() << "}";
   }
 
@@ -746,12 +741,12 @@ static LogicalResult printOperation(CppEmitter &emitter,
         return failure();
     }
     for (Operation &op : block.getOperations()) {
-      // When generating code for an emitc.if or cf.cond_br op no semicolon
-      // needs to be printed after the closing brace.
+      // When generating code for an scf.if or cf.cond_br op no semicolon needs
+      // to be printed after the closing brace.
       // When generating code for an scf.for op, printing a trailing semicolon
       // is handled within the printOperation function.
       bool trailingSemicolon =
-          !isa<cf::CondBranchOp, emitc::LiteralOp, emitc::IfOp, scf::ForOp>(op);
+          !isa<cf::CondBranchOp, emitc::LiteralOp, scf::IfOp, scf::ForOp>(op);
 
       if (failed(emitter.emitOperation(
               op, /*trailingSemicolon=*/trailingSemicolon)))
@@ -1013,16 +1008,15 @@ LogicalResult CppEmitter::emitOperation(Operation &op, bool trailingSemicolon) {
           .Case<cf::BranchOp, cf::CondBranchOp>(
               [&](auto op) { return printOperation(*this, op); })
           // EmitC ops.
-          .Case<emitc::AddOp, emitc::ApplyOp, emitc::AssignOp, emitc::CallOp,
-                emitc::CastOp, emitc::CmpOp, emitc::ConstantOp, emitc::DivOp,
-                emitc::IfOp, emitc::IncludeOp, emitc::MulOp, emitc::RemOp,
-                emitc::SubOp, emitc::VariableOp>(
+          .Case<emitc::AddOp, emitc::ApplyOp, emitc::CallOp, emitc::CastOp,
+                emitc::CmpOp, emitc::ConstantOp, emitc::DivOp, emitc::IncludeOp,
+                emitc::MulOp, emitc::RemOp, emitc::SubOp, emitc::VariableOp>(
               [&](auto op) { return printOperation(*this, op); })
           // Func ops.
           .Case<func::CallOp, func::ConstantOp, func::FuncOp, func::ReturnOp>(
               [&](auto op) { return printOperation(*this, op); })
           // SCF ops.
-          .Case<scf::ForOp, scf::YieldOp>(
+          .Case<scf::ForOp, scf::IfOp, scf::YieldOp>(
               [&](auto op) { return printOperation(*this, op); })
           // Arithmetic ops.
           .Case<arith::ConstantOp>(

diff  --git a/mlir/test/Conversion/SCFToEmitC/if.mlir b/mlir/test/Conversion/SCFToEmitC/if.mlir
deleted file mode 100644
index e34fd6a5efa4985..000000000000000
--- a/mlir/test/Conversion/SCFToEmitC/if.mlir
+++ /dev/null
@@ -1,70 +0,0 @@
-// RUN: mlir-opt -allow-unregistered-dialect -convert-scf-to-emitc %s | FileCheck %s
-
-func.func @test_if(%arg0: i1, %arg1: f32) {
-  scf.if %arg0 {
-     %0 = emitc.call "func_const"(%arg1) : (f32) -> i32
-  }
-  return
-}
-// CHECK-LABEL: func.func @test_if(
-// CHECK-SAME:                     %[[VAL_0:.*]]: i1,
-// CHECK-SAME:                     %[[VAL_1:.*]]: f32) {
-// CHECK-NEXT:    emitc.if %[[VAL_0]] {
-// CHECK-NEXT:      %[[VAL_2:.*]] = emitc.call "func_const"(%[[VAL_1]]) : (f32) -> i32
-// CHECK-NEXT:    }
-// CHECK-NEXT:    return
-// CHECK-NEXT:  }
-
-
-func.func @test_if_else(%arg0: i1, %arg1: f32) {
-  scf.if %arg0 {
-    %0 = emitc.call "func_true"(%arg1) : (f32) -> i32
-  } else {
-    %0 = emitc.call "func_false"(%arg1) : (f32) -> i32
-  }
-  return
-}
-// CHECK-LABEL: func.func @test_if_else(
-// CHECK-SAME:                          %[[VAL_0:.*]]: i1,
-// CHECK-SAME:                          %[[VAL_1:.*]]: f32) {
-// CHECK-NEXT:    emitc.if %[[VAL_0]] {
-// CHECK-NEXT:      %[[VAL_2:.*]] = emitc.call "func_true"(%[[VAL_1]]) : (f32) -> i32
-// CHECK-NEXT:    } else {
-// CHECK-NEXT:      %[[VAL_3:.*]] = emitc.call "func_false"(%[[VAL_1]]) : (f32) -> i32
-// CHECK-NEXT:    }
-// CHECK-NEXT:    return
-// CHECK-NEXT:  }
-
-
-func.func @test_if_yield(%arg0: i1, %arg1: f32) {
-  %0 = arith.constant 0 : i8
-  %x, %y = scf.if %arg0 -> (i32, f64) {
-    %1 = emitc.call "func_true_1"(%arg1) : (f32) -> i32
-    %2 = emitc.call "func_true_2"(%arg1) : (f32) -> f64
-    scf.yield %1, %2 : i32, f64
-  } else {
-    %1 = emitc.call "func_false_1"(%arg1) : (f32) -> i32
-    %2 = emitc.call "func_false_2"(%arg1) : (f32) -> f64
-    scf.yield %1, %2 : i32, f64
-  }
-  return
-}
-// CHECK-LABEL: func.func @test_if_yield(
-// CHECK-SAME:                           %[[VAL_0:.*]]: i1,
-// CHECK-SAME:                           %[[VAL_1:.*]]: f32) {
-// CHECK-NEXT:    %[[VAL_2:.*]] = arith.constant 0 : i8
-// CHECK-NEXT:    %[[VAL_3:.*]] = "emitc.variable"() <{value = #emitc.opaque<"">}> : () -> i32
-// CHECK-NEXT:    %[[VAL_4:.*]] = "emitc.variable"() <{value = #emitc.opaque<"">}> : () -> f64
-// CHECK-NEXT:    emitc.if %[[VAL_0]] {
-// CHECK-NEXT:      %[[VAL_5:.*]] = emitc.call "func_true_1"(%[[VAL_1]]) : (f32) -> i32
-// CHECK-NEXT:      %[[VAL_6:.*]] = emitc.call "func_true_2"(%[[VAL_1]]) : (f32) -> f64
-// CHECK-NEXT:      emitc.assign %[[VAL_5]] : i32 to %[[VAL_3]] : i32
-// CHECK-NEXT:      emitc.assign %[[VAL_6]] : f64 to %[[VAL_4]] : f64
-// CHECK-NEXT:    } else {
-// CHECK-NEXT:      %[[VAL_7:.*]] = emitc.call "func_false_1"(%[[VAL_1]]) : (f32) -> i32
-// CHECK-NEXT:      %[[VAL_8:.*]] = emitc.call "func_false_2"(%[[VAL_1]]) : (f32) -> f64
-// CHECK-NEXT:      emitc.assign %[[VAL_7]] : i32 to %[[VAL_3]] : i32
-// CHECK-NEXT:      emitc.assign %[[VAL_8]] : f64 to %[[VAL_4]] : f64
-// CHECK-NEXT:    }
-// CHECK-NEXT:    return
-// CHECK-NEXT:  }

diff  --git a/mlir/test/Dialect/EmitC/invalid_ops.mlir b/mlir/test/Dialect/EmitC/invalid_ops.mlir
index 9e8f0bf0bf8bdcd..3978f906525b884 100644
--- a/mlir/test/Dialect/EmitC/invalid_ops.mlir
+++ b/mlir/test/Dialect/EmitC/invalid_ops.mlir
@@ -199,28 +199,3 @@ func.func @sub_pointer_pointer(%arg0: !emitc.ptr<f32>, %arg1: !emitc.ptr<f32>) {
     %1 = "emitc.sub" (%arg0, %arg1) : (!emitc.ptr<f32>, !emitc.ptr<f32>) -> !emitc.ptr<f32>
     return
 }
-
-// -----
-
-func.func @test_misplaced_yield() {
-  // expected-error @+1 {{'emitc.yield' op expects parent op 'emitc.if'}}
-  emitc.yield
-  return
-}
-
-// -----
-
-func.func @test_assign_to_non_variable(%arg1: f32, %arg2: f32) {
-  // expected-error @+1 {{'emitc.assign' op requires first operand (<block argument> of type 'f32' at index: 1) to be a Variable}}
-  emitc.assign %arg1 : f32 to %arg2 : f32
-  return
-}
-
-// -----
-
-func.func @test_assign_type_mismatch(%arg1: f32) {
-  %v = "emitc.variable"() <{value = #emitc.opaque<"">}> : () -> i32
-  // expected-error @+1 {{'emitc.assign' op requires value's type ('f32') to match variable's type ('i32')}}
-  emitc.assign %arg1 : f32 to %v : i32
-  return
-}

diff  --git a/mlir/test/Dialect/EmitC/ops.mlir b/mlir/test/Dialect/EmitC/ops.mlir
index 0817945e3b1e0bc..279fe13229c594e 100644
--- a/mlir/test/Dialect/EmitC/ops.mlir
+++ b/mlir/test/Dialect/EmitC/ops.mlir
@@ -97,33 +97,3 @@ func.func @cmp(%arg0 : i32, %arg1 : f32, %arg2 : i64, %arg3 : f64, %arg4 : !emit
   %14 = emitc.cmp three_way, %arg6, %arg6 : (!emitc.opaque<"custom">, !emitc.opaque<"custom">) -> !emitc.opaque<"custom">
   return
 }
-
-func.func @test_if(%arg0: i1, %arg1: f32) {
-  emitc.if %arg0 {
-     %0 = emitc.call "func_const"(%arg1) : (f32) -> i32
-  }
-  return
-}
-
-func.func @test_explicit_yield(%arg0: i1, %arg1: f32) {
-  emitc.if %arg0 {
-     %0 = emitc.call "func_const"(%arg1) : (f32) -> i32
-     emitc.yield
-  }
-  return
-}
-
-func.func @test_if_else(%arg0: i1, %arg1: f32) {
-  emitc.if %arg0 {
-    %0 = emitc.call "func_true"(%arg1) : (f32) -> i32
-  } else {
-    %0 = emitc.call "func_false"(%arg1) : (f32) -> i32
-  }
-  return
-}
-
-func.func @test_assign(%arg1: f32) {
-  %v = "emitc.variable"() <{value = #emitc.opaque<"">}> : () -> f32
-  emitc.assign %arg1 : f32 to %v : f32
-  return
-}

diff  --git a/mlir/test/Target/Cpp/if.mlir b/mlir/test/Target/Cpp/if.mlir
index beff2182777b42d..74fcb7104228f08 100644
--- a/mlir/test/Target/Cpp/if.mlir
+++ b/mlir/test/Target/Cpp/if.mlir
@@ -2,7 +2,7 @@
 // RUN: mlir-translate -mlir-to-cpp -declare-variables-at-top %s | FileCheck %s -check-prefix=CPP-DECLTOP
 
 func.func @test_if(%arg0: i1, %arg1: f32) {
-  emitc.if %arg0 {
+  scf.if %arg0 {
      %0 = emitc.call "func_const"(%arg1) : (f32) -> i32
   }
   return
@@ -10,6 +10,7 @@ func.func @test_if(%arg0: i1, %arg1: f32) {
 // CPP-DEFAULT: void test_if(bool [[V0:[^ ]*]], float [[V1:[^ ]*]]) {
 // CPP-DEFAULT-NEXT: if ([[V0]]) {
 // CPP-DEFAULT-NEXT: int32_t [[V2:[^ ]*]] = func_const([[V1]]);
+// CPP-DEFAULT-NEXT: ;
 // CPP-DEFAULT-NEXT: }
 // CPP-DEFAULT-NEXT: return;
 
@@ -17,12 +18,13 @@ func.func @test_if(%arg0: i1, %arg1: f32) {
 // CPP-DECLTOP-NEXT: int32_t [[V2:[^ ]*]];
 // CPP-DECLTOP-NEXT: if ([[V0]]) {
 // CPP-DECLTOP-NEXT: [[V2]] = func_const([[V1]]);
+// CPP-DECLTOP-NEXT: ;
 // CPP-DECLTOP-NEXT: }
 // CPP-DECLTOP-NEXT: return;
 
 
 func.func @test_if_else(%arg0: i1, %arg1: f32) {
-  emitc.if %arg0 {
+  scf.if %arg0 {
     %0 = emitc.call "func_true"(%arg1) : (f32) -> i32
   } else {
     %0 = emitc.call "func_false"(%arg1) : (f32) -> i32
@@ -32,8 +34,10 @@ func.func @test_if_else(%arg0: i1, %arg1: f32) {
 // CPP-DEFAULT: void test_if_else(bool [[V0:[^ ]*]], float [[V1:[^ ]*]]) {
 // CPP-DEFAULT-NEXT: if ([[V0]]) {
 // CPP-DEFAULT-NEXT: int32_t [[V2:[^ ]*]] = func_true([[V1]]);
+// CPP-DEFAULT-NEXT: ;
 // CPP-DEFAULT-NEXT: } else {
 // CPP-DEFAULT-NEXT: int32_t [[V3:[^ ]*]] = func_false([[V1]]);
+// CPP-DEFAULT-NEXT: ;
 // CPP-DEFAULT-NEXT: }
 // CPP-DEFAULT-NEXT: return;
 
@@ -42,26 +46,24 @@ func.func @test_if_else(%arg0: i1, %arg1: f32) {
 // CPP-DECLTOP-NEXT: int32_t [[V3:[^ ]*]];
 // CPP-DECLTOP-NEXT: if ([[V0]]) {
 // CPP-DECLTOP-NEXT: [[V2]] = func_true([[V1]]);
+// CPP-DECLTOP-NEXT: ;
 // CPP-DECLTOP-NEXT: } else {
 // CPP-DECLTOP-NEXT: [[V3]] = func_false([[V1]]);
+// CPP-DECLTOP-NEXT: ;
 // CPP-DECLTOP-NEXT: }
 // CPP-DECLTOP-NEXT: return;
 
 
 func.func @test_if_yield(%arg0: i1, %arg1: f32) {
   %0 = arith.constant 0 : i8
-  %x = "emitc.variable"() <{value = #emitc.opaque<"">}> : () -> i32
-  %y = "emitc.variable"() <{value = #emitc.opaque<"">}> : () -> f64
-  emitc.if %arg0 {
+  %x, %y = scf.if %arg0 -> (i32, f64) {
     %1 = emitc.call "func_true_1"(%arg1) : (f32) -> i32
     %2 = emitc.call "func_true_2"(%arg1) : (f32) -> f64
-    emitc.assign %1 : i32 to %x : i32
-    emitc.assign %2 : f64 to %y : f64
+    scf.yield %1, %2 : i32, f64
   } else {
     %1 = emitc.call "func_false_1"(%arg1) : (f32) -> i32
     %2 = emitc.call "func_false_2"(%arg1) : (f32) -> f64
-    emitc.assign %1 : i32 to %x : i32
-    emitc.assign %2 : f64 to %y : f64
+    scf.yield %1, %2 : i32, f64
   }
   return
 }
@@ -91,8 +93,6 @@ func.func @test_if_yield(%arg0: i1, %arg1: f32) {
 // CPP-DECLTOP-NEXT: int32_t [[V7:[^ ]*]];
 // CPP-DECLTOP-NEXT: double [[V8:[^ ]*]];
 // CPP-DECLTOP-NEXT: [[V2]] = 0;
-// CPP-DECLTOP-NEXT: ;
-// CPP-DECLTOP-NEXT: ;
 // CPP-DECLTOP-NEXT: if ([[V0]]) {
 // CPP-DECLTOP-NEXT: [[V5]] = func_true_1([[V1]]);
 // CPP-DECLTOP-NEXT: [[V6]] = func_true_2([[V1]]);


        


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