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

[Simon Camphausen]

https://github.com/simon-camp updated https://github.com/llvm/llvm-project/pull/93549

>From 9c5f7974b61b19cd5fe4bb7de6fc184e636a7b0e Mon Sep 17 00:00:00 2001
From: Simon Camphausen <simon.camphausen at iml.fraunhofer.de>
Date: Tue, 28 May 2024 13:36:11 +0000
Subject: [PATCH 1/2] [mlir][EmitC] Fix evaluation order of expressions

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.
---
 mlir/lib/Target/Cpp/TranslateToCpp.cpp |  6 +++++-
 mlir/test/Target/Cpp/expressions.mlir  | 17 +++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

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]+]];

>From d87cfd58dc8b47da6a633031832b5c9b818bdb8d Mon Sep 17 00:00:00 2001
From: Simon Camphausen <simon.camphausen at iml.fraunhofer.de>
Date: Wed, 29 May 2024 06:39:11 +0000
Subject: [PATCH 2/2] Review comment

---
 mlir/lib/Target/Cpp/TranslateToCpp.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mlir/lib/Target/Cpp/TranslateToCpp.cpp b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
index 3e7cd30853a98..221603c71ba59 100644
--- a/mlir/lib/Target/Cpp/TranslateToCpp.cpp
+++ b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
@@ -1317,9 +1317,9 @@ LogicalResult CppEmitter::emitOperand(Value value) {
     if (failed(precedence))
       return failure();
 
-    // 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.
+    // Sub-expressions with equal or lower 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 << "(";