[llvm] [CodeGen] Fix non-determinism in MachineBlockHashInfo hashes (PR #192826)

[Vitaly Buka via llvm-commits]

https://github.com/vitalybuka updated https://github.com/llvm/llvm-project/pull/192826

>From 7de6ee285c3a165772683994b92e63e1d9b1a90e Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka at google.com>
Date: Sat, 18 Apr 2026 21:44:41 -0700
Subject: [PATCH 1/3] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20ch?=
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Created using spr 1.3.7

[skip ci]
---
 .../CodeGen/BasicBlockMatchingAndInference.cpp  |  4 ++--
 llvm/lib/CodeGen/MachineBlockHashInfo.cpp       | 17 +++++++++--------
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/llvm/lib/CodeGen/BasicBlockMatchingAndInference.cpp b/llvm/lib/CodeGen/BasicBlockMatchingAndInference.cpp
index bba4c4a220d9e..d956bd475c9e6 100644
--- a/llvm/lib/CodeGen/BasicBlockMatchingAndInference.cpp
+++ b/llvm/lib/CodeGen/BasicBlockMatchingAndInference.cpp
@@ -19,12 +19,12 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/BasicBlockMatchingAndInference.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/CodeGen/BasicBlockSectionsProfileReader.h"
 #include "llvm/CodeGen/MachineBlockHashInfo.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/InitializePasses.h"
 #include <llvm/Support/CommandLine.h>
-#include <unordered_map>
 
 using namespace llvm;
 
@@ -70,7 +70,7 @@ class StaleMatcher {
 
 private:
   using HashBlockPairType = std::pair<BlendedBlockHash, MachineBasicBlock *>;
-  std::unordered_map<uint16_t, std::vector<HashBlockPairType>> OpHashToBlocks;
+  DenseMap<uint16_t, std::vector<HashBlockPairType>> OpHashToBlocks;
 };
 
 INITIALIZE_PASS_BEGIN(BasicBlockMatchingAndInference,
diff --git a/llvm/lib/CodeGen/MachineBlockHashInfo.cpp b/llvm/lib/CodeGen/MachineBlockHashInfo.cpp
index 73dfc7c62a95c..3aa3823731396 100644
--- a/llvm/lib/CodeGen/MachineBlockHashInfo.cpp
+++ b/llvm/lib/CodeGen/MachineBlockHashInfo.cpp
@@ -17,7 +17,7 @@
 
 using namespace llvm;
 
-uint64_t hashBlock(const MachineBasicBlock &MBB, bool HashOperands) {
+static uint64_t hashBlock(const MachineBasicBlock &MBB, bool HashOperands) {
   uint64_t Hash = 0;
   for (const MachineInstr &MI : MBB) {
     if (MI.isMetaInstruction() || MI.isTerminator())
@@ -34,7 +34,7 @@ uint64_t hashBlock(const MachineBasicBlock &MBB, bool HashOperands) {
 }
 
 /// Fold a 64-bit integer to a 16-bit one.
-uint16_t fold_64_to_16(const uint64_t Value) {
+static uint16_t fold_64_to_16(const uint64_t Value) {
   uint16_t Res = static_cast<uint16_t>(Value);
   Res ^= static_cast<uint16_t>(Value >> 16);
   Res ^= static_cast<uint16_t>(Value >> 32);
@@ -66,18 +66,19 @@ bool MachineBlockHashInfo::runOnMachineFunction(MachineFunction &F) {
   uint16_t Offset = 0;
   // Initialize hash components
   for (const MachineBasicBlock &MBB : F) {
+    auto &HashInfo = HashInfos[&MBB];
     // offset of the machine basic block
-    HashInfos[&MBB].Offset = Offset;
-    Offset += MBB.size();
+    HashInfo.Offset = Offset + MBB.size();
     // Hashing opcodes
-    HashInfos[&MBB].OpcodeHash = hashBlock(MBB, /*HashOperands=*/false);
+    HashInfo.OpcodeHash = hashBlock(MBB, /*HashOperands=*/false);
     // Hash complete instructions
-    HashInfos[&MBB].InstrHash = hashBlock(MBB, /*HashOperands=*/true);
+    HashInfo.InstrHash = hashBlock(MBB, /*HashOperands=*/true);
   }
 
   // Initialize neighbor hash
   for (const MachineBasicBlock &MBB : F) {
-    uint64_t Hash = HashInfos[&MBB].OpcodeHash;
+    auto &HashInfo = HashInfos[&MBB];
+    uint64_t Hash = HashInfo.OpcodeHash;
     // Append hashes of successors
     for (const MachineBasicBlock *SuccMBB : MBB.successors()) {
       uint64_t SuccHash = HashInfos[SuccMBB].OpcodeHash;
@@ -88,7 +89,7 @@ bool MachineBlockHashInfo::runOnMachineFunction(MachineFunction &F) {
       uint64_t PredHash = HashInfos[PredMBB].OpcodeHash;
       Hash = hashing::detail::hash_16_bytes(Hash, PredHash);
     }
-    HashInfos[&MBB].NeighborHash = Hash;
+    HashInfo.NeighborHash = Hash;
   }
 
   // Assign hashes

>From 4c11ef77e835061eb2a12c93f3f81904ee9829dd Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka at google.com>
Date: Sun, 19 Apr 2026 00:16:50 -0700
Subject: [PATCH 2/3] fix

Created using spr 1.3.7
---
 llvm/lib/CodeGen/MachineBlockHashInfo.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/lib/CodeGen/MachineBlockHashInfo.cpp b/llvm/lib/CodeGen/MachineBlockHashInfo.cpp
index 804986dac6ad2..2ad31d4fd87a8 100644
--- a/llvm/lib/CodeGen/MachineBlockHashInfo.cpp
+++ b/llvm/lib/CodeGen/MachineBlockHashInfo.cpp
@@ -43,7 +43,7 @@ static uint64_t hashValue(const APInt &I) {
   return hashValue(ArrayRef(I.getRawData(), I.getNumWords()));
 }
 
-template <typename T> static uint64_t ignoreValue(const T *I) { return 1; }
+template <typename T> static uint64_t ignoreValue(const T *) { return 1; }
 
 static uint64_t hashCombine() { return 0; }
 

>From 1980cac4b3a5cc3fb712ea626ed29f0397593d88 Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka at google.com>
Date: Sun, 19 Apr 2026 00:28:27 -0700
Subject: [PATCH 3/3] include

Created using spr 1.3.7
---
 llvm/lib/CodeGen/MachineBlockHashInfo.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/llvm/lib/CodeGen/MachineBlockHashInfo.cpp b/llvm/lib/CodeGen/MachineBlockHashInfo.cpp
index 2ad31d4fd87a8..b72a1a57b6435 100644
--- a/llvm/lib/CodeGen/MachineBlockHashInfo.cpp
+++ b/llvm/lib/CodeGen/MachineBlockHashInfo.cpp
@@ -14,6 +14,7 @@
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/CodeGen/Passes.h"
+#include "llvm/IR/Constants.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Target/TargetMachine.h"