[Mlir-commits] [mlir] [mlir][complex] Fix miscompile with log(exp) fold (PR #212781)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-mlir-complex

Author: Bryth (Brythzz)

<details>
<summary>Changes</summary>

The complex folder `log(exp(z)) -> z` leads to a miscompile if |Im(z)| \> pi since `clog` is expected to return the principal value of the complex log, whose imaginary part is in `(pi, pi]`.

Since we cannot assume properties on `z`, this PR removes the incorrect folder and updates the associated test.

---
Full diff: https://github.com/llvm/llvm-project/pull/212781.diff


3 Files Affected:

- (modified) mlir/include/mlir/Dialect/Complex/IR/ComplexOps.td (-2) 
- (modified) mlir/lib/Dialect/Complex/IR/ComplexOps.cpp (-12) 
- (modified) mlir/test/Dialect/Complex/canonicalize.mlir (+4-3) 


``````````diff
diff --git a/mlir/include/mlir/Dialect/Complex/IR/ComplexOps.td b/mlir/include/mlir/Dialect/Complex/IR/ComplexOps.td
index 828379ded14b3..e0085a124bcd6 100644
--- a/mlir/include/mlir/Dialect/Complex/IR/ComplexOps.td
+++ b/mlir/include/mlir/Dialect/Complex/IR/ComplexOps.td
@@ -337,8 +337,6 @@ def LogOp : ComplexUnaryOp<"log", [SameOperandsAndResultType]> {
   }];
 
   let results = (outs Complex<AnyFloat>:$result);
-
-  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
diff --git a/mlir/lib/Dialect/Complex/IR/ComplexOps.cpp b/mlir/lib/Dialect/Complex/IR/ComplexOps.cpp
index b5323597b7ca4..29a9a42af80d4 100644
--- a/mlir/lib/Dialect/Complex/IR/ComplexOps.cpp
+++ b/mlir/lib/Dialect/Complex/IR/ComplexOps.cpp
@@ -307,18 +307,6 @@ OpFoldResult NegOp::fold(FoldAdaptor adaptor) {
   return {};
 }
 
-//===----------------------------------------------------------------------===//
-// LogOp
-//===----------------------------------------------------------------------===//
-
-OpFoldResult LogOp::fold(FoldAdaptor adaptor) {
-  // complex.log(complex.exp(a)) -> a
-  if (auto expOp = getOperand().getDefiningOp<ExpOp>())
-    return expOp.getOperand();
-
-  return {};
-}
-
 //===----------------------------------------------------------------------===//
 // ExpOp
 //===----------------------------------------------------------------------===//
diff --git a/mlir/test/Dialect/Complex/canonicalize.mlir b/mlir/test/Dialect/Complex/canonicalize.mlir
index 1c5216c82e5c3..aad1b10e0076f 100644
--- a/mlir/test/Dialect/Complex/canonicalize.mlir
+++ b/mlir/test/Dialect/Complex/canonicalize.mlir
@@ -95,13 +95,14 @@ func.func @complex_neg_neg() -> complex<f32> {
   return %neg2 : complex<f32>
 }
 
+// This identity is correct iff |Im(z)| <= pi
 // CHECK-LABEL: func @complex_log_exp
 func.func @complex_log_exp() -> complex<f32> {
-  %complex1 = complex.constant [1.0 : f32, 0.0 : f32] : complex<f32>
-  // CHECK: %[[CPLX:.*]] = complex.constant [1.000000e+00 : f32, 0.000000e+00 : f32] : complex<f32>
-  // CHECK-NEXT: return %[[CPLX:.*]] : complex<f32>
+  %complex1 = complex.constant [0.0 : f32, 4.0 : f32] : complex<f32>
+  // CHECK: %[[CPLX:.*]] = complex.constant [0.000000e+00 : f32, 4.000000e+00 : f32] : complex<f32>
   %exp = complex.exp %complex1 : complex<f32>
   %log = complex.log %exp : complex<f32>
+  // CHECK-NOT: return %[[CPLX]] : complex<f32>
   return %log : complex<f32>
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/212781