[llvm] [BFI] Use MapVector in combineWeightsByHashing. (PR #227027)
Florian Hahn via llvm-commits
llvm-commits at lists.llvm.org
Tue Sep 29 01:59:05 PDT 2026
https://github.com/fhahn updated https://github.com/llvm/llvm-project/pull/227027
>From 734eb9c4d2b98dde12e395fe03240a44a7a26b35 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Mon, 28 Sep 2026 16:24:28 +0100
Subject: [PATCH 1/2] Precommit test
---
.../many-successors-order.ll | 156 ++++++++++++++++++
1 file changed, 156 insertions(+)
create mode 100644 llvm/test/Analysis/BlockFrequencyInfo/many-successors-order.ll
diff --git a/llvm/test/Analysis/BlockFrequencyInfo/many-successors-order.ll b/llvm/test/Analysis/BlockFrequencyInfo/many-successors-order.ll
new file mode 100644
index 0000000000000..cd9cda2151c79
--- /dev/null
+++ b/llvm/test/Analysis/BlockFrequencyInfo/many-successors-order.ll
@@ -0,0 +1,156 @@
+; RUN: opt < %s -passes='print<block-freq>' -disable-output 2>&1 | FileCheck %s
+
+; Blocks with more than 128 successor edges combine duplicate edges via a map.
+; Make sure that distributing the mass does not depend on the iteration order.
+
+; CHECK-LABEL: block-frequency-info: f
+; CHECK-NEXT: - entry: float = 1.0, int = [[ENTRY:[0-9]+]]
+; CHECK-NEXT: - default: float = 0.0077519, int = {{[0-9]+}}
+; CHECK-NEXT: - b0: float = 0.49612, int = 8937376004318074
+; CHECK-NEXT: - b1: float = 0.49612, int = 8937376004964352
+; CHECK-NEXT: - exit: float = 1.0, int = [[ENTRY]]
+define void @f(i32 %x) {
+entry:
+ switch i32 %x, label %default [
+ i32 0, label %b0
+ i32 1, label %b1
+ i32 2, label %b0
+ i32 3, label %b1
+ i32 4, label %b0
+ i32 5, label %b1
+ i32 6, label %b0
+ i32 7, label %b1
+ i32 8, label %b0
+ i32 9, label %b1
+ i32 10, label %b0
+ i32 11, label %b1
+ i32 12, label %b0
+ i32 13, label %b1
+ i32 14, label %b0
+ i32 15, label %b1
+ i32 16, label %b0
+ i32 17, label %b1
+ i32 18, label %b0
+ i32 19, label %b1
+ i32 20, label %b0
+ i32 21, label %b1
+ i32 22, label %b0
+ i32 23, label %b1
+ i32 24, label %b0
+ i32 25, label %b1
+ i32 26, label %b0
+ i32 27, label %b1
+ i32 28, label %b0
+ i32 29, label %b1
+ i32 30, label %b0
+ i32 31, label %b1
+ i32 32, label %b0
+ i32 33, label %b1
+ i32 34, label %b0
+ i32 35, label %b1
+ i32 36, label %b0
+ i32 37, label %b1
+ i32 38, label %b0
+ i32 39, label %b1
+ i32 40, label %b0
+ i32 41, label %b1
+ i32 42, label %b0
+ i32 43, label %b1
+ i32 44, label %b0
+ i32 45, label %b1
+ i32 46, label %b0
+ i32 47, label %b1
+ i32 48, label %b0
+ i32 49, label %b1
+ i32 50, label %b0
+ i32 51, label %b1
+ i32 52, label %b0
+ i32 53, label %b1
+ i32 54, label %b0
+ i32 55, label %b1
+ i32 56, label %b0
+ i32 57, label %b1
+ i32 58, label %b0
+ i32 59, label %b1
+ i32 60, label %b0
+ i32 61, label %b1
+ i32 62, label %b0
+ i32 63, label %b1
+ i32 64, label %b0
+ i32 65, label %b1
+ i32 66, label %b0
+ i32 67, label %b1
+ i32 68, label %b0
+ i32 69, label %b1
+ i32 70, label %b0
+ i32 71, label %b1
+ i32 72, label %b0
+ i32 73, label %b1
+ i32 74, label %b0
+ i32 75, label %b1
+ i32 76, label %b0
+ i32 77, label %b1
+ i32 78, label %b0
+ i32 79, label %b1
+ i32 80, label %b0
+ i32 81, label %b1
+ i32 82, label %b0
+ i32 83, label %b1
+ i32 84, label %b0
+ i32 85, label %b1
+ i32 86, label %b0
+ i32 87, label %b1
+ i32 88, label %b0
+ i32 89, label %b1
+ i32 90, label %b0
+ i32 91, label %b1
+ i32 92, label %b0
+ i32 93, label %b1
+ i32 94, label %b0
+ i32 95, label %b1
+ i32 96, label %b0
+ i32 97, label %b1
+ i32 98, label %b0
+ i32 99, label %b1
+ i32 100, label %b0
+ i32 101, label %b1
+ i32 102, label %b0
+ i32 103, label %b1
+ i32 104, label %b0
+ i32 105, label %b1
+ i32 106, label %b0
+ i32 107, label %b1
+ i32 108, label %b0
+ i32 109, label %b1
+ i32 110, label %b0
+ i32 111, label %b1
+ i32 112, label %b0
+ i32 113, label %b1
+ i32 114, label %b0
+ i32 115, label %b1
+ i32 116, label %b0
+ i32 117, label %b1
+ i32 118, label %b0
+ i32 119, label %b1
+ i32 120, label %b0
+ i32 121, label %b1
+ i32 122, label %b0
+ i32 123, label %b1
+ i32 124, label %b0
+ i32 125, label %b1
+ i32 126, label %b0
+ i32 127, label %b1
+ ]
+
+default:
+ br label %exit
+
+b0:
+ br label %exit
+
+b1:
+ br label %exit
+
+exit:
+ ret void
+}
>From a9759b22622203dc2b7d3bdd52e7632ad7fc8bda Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Sat, 26 Sep 2026 07:28:34 +0100
Subject: [PATCH 2/2] [BFI] Use MapVector in combineWeightsByHashing.
combineWeightsByHashing iterated over a DenseMap, which depends on the
hash. Use MapVector to get consistent results, independent of index
type/values.
---
llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp | 9 +++------
.../Analysis/BlockFrequencyInfo/many-successors-order.ll | 4 ++--
2 files changed, 5 insertions(+), 8 deletions(-)
diff --git a/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp b/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
index 27c52afc3baab..66c36f36d7d92 100644
--- a/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
+++ b/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
@@ -12,7 +12,7 @@
#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
#include "llvm/ADT/APInt.h"
-#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Config/llvm-config.h"
@@ -197,10 +197,8 @@ static void combineWeightsBySorting(WeightList &Weights) {
}
static void combineWeightsByHashing(WeightList &Weights) {
- // Collect weights into a DenseMap.
- using HashTable = DenseMap<BlockNode::IndexType, Weight>;
-
- HashTable Combined(NextPowerOf2(2 * Weights.size()));
+ MapVector<BlockNode::IndexType, Weight> Combined;
+ Combined.reserve(Weights.size());
for (const Weight &W : Weights)
combineWeight(Combined[W.TargetNode.Index], W);
@@ -210,7 +208,6 @@ static void combineWeightsByHashing(WeightList &Weights) {
// Fill in the new weights.
Weights.clear();
- Weights.reserve(Combined.size());
for (const auto &I : Combined)
Weights.push_back(I.second);
}
diff --git a/llvm/test/Analysis/BlockFrequencyInfo/many-successors-order.ll b/llvm/test/Analysis/BlockFrequencyInfo/many-successors-order.ll
index cd9cda2151c79..1479d175d83d7 100644
--- a/llvm/test/Analysis/BlockFrequencyInfo/many-successors-order.ll
+++ b/llvm/test/Analysis/BlockFrequencyInfo/many-successors-order.ll
@@ -6,8 +6,8 @@
; CHECK-LABEL: block-frequency-info: f
; CHECK-NEXT: - entry: float = 1.0, int = [[ENTRY:[0-9]+]]
; CHECK-NEXT: - default: float = 0.0077519, int = {{[0-9]+}}
-; CHECK-NEXT: - b0: float = 0.49612, int = 8937376004318074
-; CHECK-NEXT: - b1: float = 0.49612, int = 8937376004964352
+; CHECK-NEXT: - b0: float = 0.49612, int = [[B:[0-9]+]]
+; CHECK-NEXT: - b1: float = 0.49612, int = [[B]]
; CHECK-NEXT: - exit: float = 1.0, int = [[ENTRY]]
define void @f(i32 %x) {
entry:
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