[mlir][spirv] Use MapVector for BlockMergeInfoMap

[IgWod-IMG]

This should ensure that the structurizer while loop is deterministic across runs. Use of MapVector addresses the source of the nondeterminism which is use of a Block* as a map key.

fixes #128547

[llvmbot]

@llvm/pr-subscribers-mlir-spirv

@llvm/pr-subscribers-mlir

Author: Igor Wodiany (IgWod-IMG)

Changes

This should ensure that the structurizer while loop is deterministic across runs. Use of MapVector addresses the source of the nondeterminism which is use of a Block* as a map key.

fixes #128547

---

Full diff: https://github.com/llvm/llvm-project/pull/169636.diff

2 Files Affected:

• (modified) mlir/lib/Target/SPIRV/Deserialization/Deserializer.cpp (-3)
• (modified) mlir/lib/Target/SPIRV/Deserialization/Deserializer.h (+3-1)

diff --git a/mlir/lib/Target/SPIRV/Deserialization/Deserializer.cpp b/mlir/lib/Target/SPIRV/Deserialization/Deserializer.cpp
index 252be796488c5..d08e7ecf326ca 100644
--- a/mlir/lib/Target/SPIRV/Deserialization/Deserializer.cpp
+++ b/mlir/lib/Target/SPIRV/Deserialization/Deserializer.cpp
@@ -2923,9 +2923,6 @@ LogicalResult spirv::Deserializer::structurizeControlFlow() {
     return failure();
   }
 
-  // TODO: This loop is non-deterministic. Iteration order may vary between runs
-  // for the same shader as the key to the map is a pointer. See:
-  // https://github.com/llvm/llvm-project/issues/128547
   while (!blockMergeInfo.empty()) {
     Block *headerBlock = blockMergeInfo.begin()->first;
     BlockMergeInfo mergeInfo = blockMergeInfo.begin()->second;
diff --git a/mlir/lib/Target/SPIRV/Deserialization/Deserializer.h b/mlir/lib/Target/SPIRV/Deserialization/Deserializer.h
index 243e6fd70ae43..6d09d556c4d02 100644
--- a/mlir/lib/Target/SPIRV/Deserialization/Deserializer.h
+++ b/mlir/lib/Target/SPIRV/Deserialization/Deserializer.h
@@ -58,7 +58,9 @@ struct DebugLine {
 };
 
 /// Map from a selection/loop's header block to its merge (and continue) target.
-using BlockMergeInfoMap = DenseMap<Block *, BlockMergeInfo>;
+/// Use `MapVector<>` to ensure a deterministic iteration order with a pointer
+/// key.
+using BlockMergeInfoMap = llvm::MapVector<Block *, BlockMergeInfo>;
 
 /// A "deferred struct type" is a struct type with one or more member types not
 /// known when the Deserializer first encounters the struct. This happens, for