[Mlir-commits] [mlir] [mlir][EmitC] Fix evaluation order of expressions (PR #93549)

[llvmlistbot at llvm.org]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-mlir

Author: Simon Camphausen (simon-camp)

<details>
<summary>Changes</summary>

Expressions with the same precedence were not paranthesized and therefore were possibly evaluated in the wrong order depending on the shape of the expression tree.

---
Full diff: https://github.com/llvm/llvm-project/pull/93549.diff


2 Files Affected:

- (modified) mlir/lib/Target/Cpp/TranslateToCpp.cpp (+5-1) 
- (modified) mlir/test/Target/Cpp/expressions.mlir (+17) 


``````````diff
diff --git a/mlir/lib/Target/Cpp/TranslateToCpp.cpp b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
index 7db7163bac4ab..3e7cd30853a98 100644
--- a/mlir/lib/Target/Cpp/TranslateToCpp.cpp
+++ b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
@@ -1316,7 +1316,11 @@ LogicalResult CppEmitter::emitOperand(Value value) {
     FailureOr<int> precedence = getOperatorPrecedence(def);
     if (failed(precedence))
       return failure();
-    bool encloseInParenthesis = precedence.value() < getExpressionPrecedence();
+
+    // Expressions with the same precedence need to be paranthesized, as
+    // they might be evaluated in the wrong order depending on the shape of the
+    // expression tree.
+    bool encloseInParenthesis = precedence.value() <= getExpressionPrecedence();
     if (encloseInParenthesis) {
       os << "(";
       pushExpressionPrecedence(lowestPrecedence());
diff --git a/mlir/test/Target/Cpp/expressions.mlir b/mlir/test/Target/Cpp/expressions.mlir
index 2eda58902cb1d..8a3bac3233a93 100644
--- a/mlir/test/Target/Cpp/expressions.mlir
+++ b/mlir/test/Target/Cpp/expressions.mlir
@@ -83,6 +83,23 @@ func.func @paranthesis_for_low_precedence(%arg0: i32, %arg1: i32, %arg2: i32) ->
   return %e : f32
 }
 
+// CPP-DEFAULT:      int32_t paranthesis_for_same_precedence(int32_t [[VAL_1:v[0-9]+]], int32_t [[VAL_2:v[0-9]+]], int32_t [[VAL_3:v[0-9]+]]) {
+// CPP-DEFAULT-NEXT:   return [[VAL_3]] / ([[VAL_1]] * [[VAL_2]]);
+// CPP-DEFAULT-NEXT: }
+
+// CPP-DECLTOP:      int32_t paranthesis_for_same_precedence(int32_t [[VAL_1:v[0-9]+]], int32_t [[VAL_2:v[0-9]+]], int32_t [[VAL_3:v[0-9]+]]) {
+// CPP-DECLTOP-NEXT:   return [[VAL_3]] / ([[VAL_1]] * [[VAL_2]]);
+// CPP-DECLTOP-NEXT: }
+func.func @paranthesis_for_same_precedence(%arg0: i32, %arg1: i32, %arg2: i32) -> i32 {
+  %e = emitc.expression : i32 {
+      %0 = emitc.mul %arg0, %arg1 : (i32, i32) -> i32
+      %1 = emitc.div %arg2, %0 : (i32, i32) -> i32
+      emitc.yield %1 : i32
+    }
+
+  return %e : i32
+}
+
 // CPP-DEFAULT:      int32_t multiple_uses(int32_t [[VAL_1:v[0-9]+]], int32_t [[VAL_2:v[0-9]+]], int32_t [[VAL_3:v[0-9]+]], int32_t [[VAL_4:v[0-9]+]]) {
 // CPP-DEFAULT-NEXT:   bool [[VAL_5:v[0-9]+]] = bar([[VAL_1]] * [[VAL_2]], [[VAL_3]]) - [[VAL_4]] < [[VAL_2]];
 // CPP-DEFAULT-NEXT:   int32_t [[VAL_6:v[0-9]+]];

``````````

</details>


https://github.com/llvm/llvm-project/pull/93549