[CIR] Upstream TernaryOp (#137184)

This patch adds TernaryOp to CIR plus a pass that flattens the operator
in FlattenCFG.

This is the first PR out of (probably) 3 wrt. TernaryOp. I split the
patches up to make reviewing them easier. As such, this PR is only about
adding the CIR operation. The next PR will be about the CodeGen bits
from the C++ conditional operator and the final one will add the
cir-simplify transform for TernaryOp and SelectOp.

---------

Co-authored-by: Morris Hafner <[email protected]>
Co-authored-by: Andy Kaylor <[email protected]>

Author: mmha

clang/include/clang/CIR/Dialect/IR/CIROps.td

@@ -610,9 +610,9 @@ def ConditionOp : CIR_Op<"condition", [
 //===----------------------------------------------------------------------===//
 
 def YieldOp : CIR_Op<"yield", [ReturnLike, Terminator,
-                               ParentOneOf<["IfOp", "ScopeOp", "SwitchOp",
-                                            "WhileOp", "ForOp", "CaseOp",
-                                            "DoWhileOp"]>]> {
+                               ParentOneOf<["CaseOp", "DoWhileOp", "ForOp",
+                                            "IfOp", "ScopeOp", "SwitchOp",
+                                            "TernaryOp", "WhileOp"]>]> {
   let summary = "Represents the default branching behaviour of a region";
   let description = [{
     The `cir.yield` operation terminates regions on different CIR operations,
@@ -1462,6 +1462,63 @@ def SelectOp : CIR_Op<"select", [Pure,
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// TernaryOp
+//===----------------------------------------------------------------------===//
+
+def TernaryOp : CIR_Op<"ternary",
+      [DeclareOpInterfaceMethods<RegionBranchOpInterface>,
+       RecursivelySpeculatable, AutomaticAllocationScope, NoRegionArguments]> {
+  let summary = "The `cond ? a : b` C/C++ ternary operation";
+  let description = [{
+    The `cir.ternary` operation represents C/C++ ternary, much like a `select`
+    operation. The first argument is a `cir.bool` condition to evaluate, followed
+    by two regions to execute (true or false). This is different from `cir.if`
+    since each region is one block sized and the `cir.yield` closing the block
+    scope should have one argument.
+
+    `cir.ternary` also represents the GNU binary conditional operator ?: which
+    reuses the parent operation for both the condition and the true branch to
+    evaluate it only once.
+
+    Example:
+
+    ```mlir
+    // cond = a && b;
+
+    %x = cir.ternary (%cond, true_region {
+      ...
+      cir.yield %a : i32
+    }, false_region {
+      ...
+      cir.yield %b : i32
+    }) -> i32
+    ```
+  }];
+  let arguments = (ins CIR_BoolType:$cond);
+  let regions = (region AnyRegion:$trueRegion,
+                        AnyRegion:$falseRegion);
+  let results = (outs Optional<CIR_AnyType>:$result);
+
+  let skipDefaultBuilders = 1;
+  let builders = [
+    OpBuilder<(ins "mlir::Value":$cond,
+      "llvm::function_ref<void(mlir::OpBuilder &, mlir::Location)>":$trueBuilder,
+      "llvm::function_ref<void(mlir::OpBuilder &, mlir::Location)>":$falseBuilder)
+      >
+  ];
+
+  // All constraints already verified elsewhere.
+  let hasVerifier = 0;
+
+  let assemblyFormat = [{
+    `(` $cond `,`
+      `true` $trueRegion `,`
+      `false` $falseRegion
+    `)` `:` functional-type(operands, results) attr-dict
+  }];
+}
+
 //===----------------------------------------------------------------------===//
 // GlobalOp
 //===----------------------------------------------------------------------===//

clang/lib/CIR/Dialect/IR/CIRDialect.cpp

@@ -1187,6 +1187,49 @@ LogicalResult cir::BinOp::verify() {
   return mlir::success();
 }
 
+//===----------------------------------------------------------------------===//
+// TernaryOp
+//===----------------------------------------------------------------------===//
+
+/// Given the region at `point`, or the parent operation if `point` 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 cir::TernaryOp::getSuccessorRegions(
+    mlir::RegionBranchPoint point, SmallVectorImpl<RegionSuccessor> &regions) {
+  // The `true` and the `false` region branch back to the parent operation.
+  if (!point.isParent()) {
+    regions.push_back(RegionSuccessor(this->getODSResults(0)));
+    return;
+  }
+
+  // When branching from the parent operation, both the true and false
+  // regions are considered possible successors
+  regions.push_back(RegionSuccessor(&getTrueRegion()));
+  regions.push_back(RegionSuccessor(&getFalseRegion()));
+}
+
+void cir::TernaryOp::build(
+    OpBuilder &builder, OperationState &result, Value cond,
+    function_ref<void(OpBuilder &, Location)> trueBuilder,
+    function_ref<void(OpBuilder &, Location)> falseBuilder) {
+  result.addOperands(cond);
+  OpBuilder::InsertionGuard guard(builder);
+  Region *trueRegion = result.addRegion();
+  Block *block = builder.createBlock(trueRegion);
+  trueBuilder(builder, result.location);
+  Region *falseRegion = result.addRegion();
+  builder.createBlock(falseRegion);
+  falseBuilder(builder, result.location);
+
+  auto yield = dyn_cast<YieldOp>(block->getTerminator());
+  assert((yield && yield.getNumOperands() <= 1) &&
+         "expected zero or one result type");
+  if (yield.getNumOperands() == 1)
+    result.addTypes(TypeRange{yield.getOperandTypes().front()});
+}
+
 //===----------------------------------------------------------------------===//
 // ShiftOp
 //===----------------------------------------------------------------------===//

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

@@ -254,10 +254,61 @@ class CIRLoopOpInterfaceFlattening
   }
 };
 
+class CIRTernaryOpFlattening : public mlir::OpRewritePattern<cir::TernaryOp> {
+public:
+  using OpRewritePattern<cir::TernaryOp>::OpRewritePattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(cir::TernaryOp op,
+                  mlir::PatternRewriter &rewriter) const override {
+    Location loc = op->getLoc();
+    Block *condBlock = rewriter.getInsertionBlock();
+    Block::iterator opPosition = rewriter.getInsertionPoint();
+    Block *remainingOpsBlock = rewriter.splitBlock(condBlock, opPosition);
+    llvm::SmallVector<mlir::Location, 2> locs;
+    // Ternary result is optional, make sure to populate the location only
+    // when relevant.
+    if (op->getResultTypes().size())
+      locs.push_back(loc);
+    Block *continueBlock =
+        rewriter.createBlock(remainingOpsBlock, op->getResultTypes(), locs);
+    rewriter.create<cir::BrOp>(loc, remainingOpsBlock);
+
+    Region &trueRegion = op.getTrueRegion();
+    Block *trueBlock = &trueRegion.front();
+    mlir::Operation *trueTerminator = trueRegion.back().getTerminator();
+    rewriter.setInsertionPointToEnd(&trueRegion.back());
+    auto trueYieldOp = dyn_cast<cir::YieldOp>(trueTerminator);
+
+    rewriter.replaceOpWithNewOp<cir::BrOp>(trueYieldOp, trueYieldOp.getArgs(),
+                                           continueBlock);
+    rewriter.inlineRegionBefore(trueRegion, continueBlock);
+
+    Block *falseBlock = continueBlock;
+    Region &falseRegion = op.getFalseRegion();
+
+    falseBlock = &falseRegion.front();
+    mlir::Operation *falseTerminator = falseRegion.back().getTerminator();
+    rewriter.setInsertionPointToEnd(&falseRegion.back());
+    auto falseYieldOp = dyn_cast<cir::YieldOp>(falseTerminator);
+    rewriter.replaceOpWithNewOp<cir::BrOp>(falseYieldOp, falseYieldOp.getArgs(),
+                                           continueBlock);
+    rewriter.inlineRegionBefore(falseRegion, continueBlock);
+
+    rewriter.setInsertionPointToEnd(condBlock);
+    rewriter.create<cir::BrCondOp>(loc, op.getCond(), trueBlock, falseBlock);
+
+    rewriter.replaceOp(op, continueBlock->getArguments());
+
+    // Ok, we're done!
+    return mlir::success();
+  }
+};
+
 void populateFlattenCFGPatterns(RewritePatternSet &patterns) {
-  patterns
-      .add<CIRIfFlattening, CIRLoopOpInterfaceFlattening, CIRScopeOpFlattening>(
-          patterns.getContext());
+  patterns.add<CIRIfFlattening, CIRLoopOpInterfaceFlattening,
+               CIRScopeOpFlattening, CIRTernaryOpFlattening>(
+      patterns.getContext());
 }
 
 void CIRFlattenCFGPass::runOnOperation() {
@@ -269,9 +320,8 @@ void CIRFlattenCFGPass::runOnOperation() {
   getOperation()->walk<mlir::WalkOrder::PostOrder>([&](Operation *op) {
     assert(!cir::MissingFeatures::ifOp());
     assert(!cir::MissingFeatures::switchOp());
-    assert(!cir::MissingFeatures::ternaryOp());
     assert(!cir::MissingFeatures::tryOp());
-    if (isa<IfOp, ScopeOp, LoopOpInterface>(op))
+    if (isa<IfOp, ScopeOp, LoopOpInterface, TernaryOp>(op))
       ops.push_back(op);
   });
 

clang/test/CIR/IR/ternary.cir

@@ -0,0 +1,30 @@
+// RUN: cir-opt %s | cir-opt | FileCheck %s
+!u32i = !cir.int<u, 32>
+
+module  {
+  cir.func @blue(%arg0: !cir.bool) -> !u32i {
+    %0 = cir.ternary(%arg0, true {
+      %a = cir.const #cir.int<0> : !u32i
+      cir.yield %a : !u32i
+    }, false {
+      %b = cir.const #cir.int<1> : !u32i
+      cir.yield %b : !u32i
+    }) : (!cir.bool) -> !u32i
+    cir.return %0 : !u32i
+  }
+}
+
+// CHECK: module  {
+
+// CHECK: cir.func @blue(%arg0: !cir.bool) -> !u32i {
+// CHECK:   %0 = cir.ternary(%arg0, true {
+// CHECK:     %1 = cir.const #cir.int<0> : !u32i
+// CHECK:     cir.yield %1 : !u32i
+// CHECK:   }, false {
+// CHECK:     %1 = cir.const #cir.int<1> : !u32i
+// CHECK:     cir.yield %1 : !u32i
+// CHECK:   }) : (!cir.bool) -> !u32i
+// CHECK:   cir.return %0 : !u32i
+// CHECK: }
+
+// CHECK: }

clang/test/CIR/Lowering/ternary.cir

@@ -0,0 +1,30 @@
+// RUN: cir-translate -cir-to-llvmir --disable-cc-lowering -o %t.ll %s
+// RUN: FileCheck --input-file=%t.ll -check-prefix=LLVM %s
+
+!u32i = !cir.int<u, 32>
+
+module  {
+  cir.func @blue(%arg0: !cir.bool) -> !u32i {
+    %0 = cir.ternary(%arg0, true {
+      %a = cir.const #cir.int<0> : !u32i
+      cir.yield %a : !u32i
+    }, false {
+      %b = cir.const #cir.int<1> : !u32i
+      cir.yield %b : !u32i
+    }) : (!cir.bool) -> !u32i
+    cir.return %0 : !u32i
+  }
+}
+
+// LLVM-LABEL: define i32 {{.*}}@blue(
+// LLVM-SAME: i1 [[PRED:%[[:alnum:]]+]])
+// LLVM:   br i1 [[PRED]], label %[[B1:[[:alnum:]]+]], label %[[B2:[[:alnum:]]+]]
+// LLVM: [[B1]]:
+// LLVM:   br label %[[M:[[:alnum:]]+]]
+// LLVM: [[B2]]:
+// LLVM:   br label %[[M]]
+// LLVM: [[M]]:
+// LLVM:   [[R:%[[:alnum:]]+]] = phi i32 [ 1, %[[B2]] ], [ 0, %[[B1]] ]
+// LLVM:   br label %[[B3:[[:alnum:]]+]]
+// LLVM: [[B3]]:
+// LLVM:   ret i32 [[R]]

clang/test/CIR/Transforms/ternary.cir

@@ -0,0 +1,68 @@
+// RUN: cir-opt %s -cir-flatten-cfg -o - | FileCheck %s
+
+!s32i = !cir.int<s, 32>
+
+module {
+  cir.func @foo(%arg0: !s32i) -> !s32i {
+    %0 = cir.alloca !s32i, !cir.ptr<!s32i>, ["y", init] {alignment = 4 : i64}
+    %1 = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"] {alignment = 4 : i64}
+    cir.store %arg0, %0 : !s32i, !cir.ptr<!s32i>
+    %2 = cir.load %0 : !cir.ptr<!s32i>, !s32i
+    %3 = cir.const #cir.int<0> : !s32i
+    %4 = cir.cmp(gt, %2, %3) : !s32i, !cir.bool
+    %5 = cir.ternary(%4, true {
+      %7 = cir.const #cir.int<3> : !s32i
+      cir.yield %7 : !s32i
+    }, false {
+      %7 = cir.const #cir.int<5> : !s32i
+      cir.yield %7 : !s32i
+    }) : (!cir.bool) -> !s32i
+    cir.store %5, %1 : !s32i, !cir.ptr<!s32i>
+    %6 = cir.load %1 : !cir.ptr<!s32i>, !s32i
+    cir.return %6 : !s32i
+  }
+
+// CHECK: cir.func @foo(%arg0: !s32i) -> !s32i {
+// CHECK:   %0 = cir.alloca !s32i, !cir.ptr<!s32i>, ["y", init] {alignment = 4 : i64}
+// CHECK:   %1 = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"] {alignment = 4 : i64}
+// CHECK:   cir.store %arg0, %0 : !s32i, !cir.ptr<!s32i>
+// CHECK:   %2 = cir.load %0 : !cir.ptr<!s32i>, !s32i
+// CHECK:   %3 = cir.const #cir.int<0> : !s32i
+// CHECK:   %4 = cir.cmp(gt, %2, %3) : !s32i, !cir.bool
+// CHECK:    cir.brcond %4 ^bb1, ^bb2
+// CHECK:  ^bb1:  // pred: ^bb0
+// CHECK:    %5 = cir.const #cir.int<3> : !s32i
+// CHECK:    cir.br ^bb3(%5 : !s32i)
+// CHECK:  ^bb2:  // pred: ^bb0
+// CHECK:    %6 = cir.const #cir.int<5> : !s32i
+// CHECK:    cir.br ^bb3(%6 : !s32i)
+// CHECK:  ^bb3(%7: !s32i):  // 2 preds: ^bb1, ^bb2
+// CHECK:    cir.br ^bb4
+// CHECK:  ^bb4:  // pred: ^bb3
+// CHECK:    cir.store %7, %1 : !s32i, !cir.ptr<!s32i>
+// CHECK:    %8 = cir.load %1 : !cir.ptr<!s32i>, !s32i
+// CHECK:    cir.return %8 : !s32i
+// CHECK:  }
+
+  cir.func @foo2(%arg0: !cir.bool) {
+    cir.ternary(%arg0, true {
+      cir.yield
+    }, false {
+      cir.yield
+    }) : (!cir.bool) -> ()
+    cir.return
+  }
+
+// CHECK: cir.func @foo2(%arg0: !cir.bool) {
+// CHECK:   cir.brcond %arg0 ^bb1, ^bb2
+// CHECK: ^bb1:  // pred: ^bb0
+// CHECK:   cir.br ^bb3
+// CHECK: ^bb2:  // pred: ^bb0
+// CHECK:   cir.br ^bb3
+// CHECK: ^bb3:  // 2 preds: ^bb1, ^bb2
+// CHECK:   cir.br ^bb4
+// CHECK: ^bb4:  // pred: ^bb3
+// CHECK:   cir.return
+// CHECK: }
+
+}