[Mlir-commits] [mlir] [mlir][emitc] Refactor brackets in expressions (PR #168267)

[Gil Rapaport]

https://github.com/aniragil created https://github.com/llvm/llvm-project/pull/168267

This patch is a minor NFC-intended refactoring to the way emitting redundant parentheses is prevented.
The current implementation pushes and later pops a fake low precedence into the precedence stack when emitting function calls. The new implementation adds a boolean argument to `emitOperand()` that explicity guarantees that the operand is being emitted between some kind of brackets, exempting the method from enforcing correct evaluation order w.r.t precedence and associativity up the expression tree.

>From 3cdfb8b14fc5d000d23d8c959ab483f11803c479 Mon Sep 17 00:00:00 2001
From: Gil Rapaport <gil.rapaport at mobileye.com>
Date: Sun, 16 Nov 2025 14:18:26 +0200
Subject: [PATCH] [mlir][emitc] Refactor brackets in expressions

This patch is a minor NFC-intended refactoring to the way emitting
redundant parentheses is prevented.
The current implementation pushes and later pops a fake low precedence
into the precedence stack when emitting function calls.
The new implementation adds a boolean argument to `emitOperand()` that
explicity guarantees that the operand is being emitted between some
kind of brackets, exempting the method from enforcing correct evaluation
order w.r.t precedence and associativity up the expression tree.
---
 mlir/lib/Target/Cpp/TranslateToCpp.cpp | 31 +++++++++++++-------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/mlir/lib/Target/Cpp/TranslateToCpp.cpp b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
index 6bd76bb1ffc4b..56f81b0bea9e2 100644
--- a/mlir/lib/Target/Cpp/TranslateToCpp.cpp
+++ b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
@@ -173,8 +173,11 @@ struct CppEmitter {
   /// Emits the operands of the operation. All operands are emitted in order.
   LogicalResult emitOperands(Operation &op);
 
-  /// Emits value as an operands of an operation
-  LogicalResult emitOperand(Value value);
+  /// Emits value as an operand of some operation. Unless \p isInBrackets is
+  /// true, operands emitted as sub-expressions will be parenthesized if needed
+  /// in order to enforce correct evaluation based on precedence and
+  /// associativity.
+  LogicalResult emitOperand(Value value, bool isInBrackets = false);
 
   /// Emit an expression as a C expression.
   LogicalResult emitExpression(ExpressionOp expressionOp);
@@ -1578,7 +1581,7 @@ LogicalResult CppEmitter::emitExpression(ExpressionOp expressionOp) {
   return success();
 }
 
-LogicalResult CppEmitter::emitOperand(Value value) {
+LogicalResult CppEmitter::emitOperand(Value value, bool isInBrackets) {
   if (isPartOfCurrentExpression(value)) {
     Operation *def = value.getDefiningOp();
     assert(def && "Expected operand to be defined by an operation");
@@ -1586,10 +1589,12 @@ LogicalResult CppEmitter::emitOperand(Value value) {
     if (failed(precedence))
       return failure();
 
-    // Sub-expressions with equal or lower precedence need to be parenthesized,
-    // as they might be evaluated in the wrong order depending on the shape of
-    // the expression tree.
-    bool encloseInParenthesis = precedence.value() <= getExpressionPrecedence();
+    // Unless already in brackets, sub-expressions with equal or lower
+    // precedence need to be parenthesized as they might be evaluated in the
+    // wrong order depending on the shape of the expression tree.
+    bool encloseInParenthesis =
+        !isInBrackets && precedence.value() <= getExpressionPrecedence();
+
     if (encloseInParenthesis)
       os << "(";
     pushExpressionPrecedence(precedence.value());
@@ -1628,15 +1633,9 @@ LogicalResult CppEmitter::emitOperand(Value value) {
 
 LogicalResult CppEmitter::emitOperands(Operation &op) {
   return interleaveCommaWithError(op.getOperands(), os, [&](Value operand) {
-    // If an expression is being emitted, push lowest precedence as these
-    // operands are either wrapped by parenthesis.
-    if (getEmittedExpression())
-      pushExpressionPrecedence(lowestPrecedence());
-    if (failed(emitOperand(operand)))
-      return failure();
-    if (getEmittedExpression())
-      popExpressionPrecedence();
-    return success();
+    // Emit operand under guarantee that if it's part of an expression then it
+    // is being emitted within brackets.
+    return emitOperand(operand, /*isInBrackets=*/true);
   });
 }