[llvm] [MemProf] Add option to hint allocations at a given cold byte percentage (PR #120301)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Teresa Johnson (teresajohnson)

<details>
<summary>Changes</summary>

Optionally unconditionally hint allocations as cold or not cold during
the matching step if the percentage of bytes allocated is at least that
of the given threshold.


---
Full diff: https://github.com/llvm/llvm-project/pull/120301.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Instrumentation/MemProfiler.cpp (+19) 
- (modified) llvm/test/Transforms/PGOProfile/memprof.ll (+12-3) 


``````````diff
diff --git a/llvm/lib/Transforms/Instrumentation/MemProfiler.cpp b/llvm/lib/Transforms/Instrumentation/MemProfiler.cpp
index c980869a1c0d82..497fe4b7594ea7 100644
--- a/llvm/lib/Transforms/Instrumentation/MemProfiler.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemProfiler.cpp
@@ -173,6 +173,10 @@ static cl::opt<std::string>
 
 extern cl::opt<bool> MemProfReportHintedSizes;
 
+static cl::opt<unsigned> MinMatchedColdBytePercent(
+    "memprof-matching-cold-threshold", cl::init(100), cl::Hidden,
+    cl::desc("Min percent of cold bytes matched to hint allocation cold"));
+
 // Instrumentation statistics
 STATISTIC(NumInstrumentedReads, "Number of instrumented reads");
 STATISTIC(NumInstrumentedWrites, "Number of instrumented writes");
@@ -1074,6 +1078,8 @@ readMemprof(Module &M, Function &F, IndexedInstrProfReader *MemProfReader,
         // contexts. Add them to a Trie specialized for trimming the contexts to
         // the minimal needed to disambiguate contexts with unique behavior.
         CallStackTrie AllocTrie;
+        uint64_t TotalSize = 0;
+        uint64_t TotalColdSize = 0;
         for (auto *AllocInfo : AllocInfoIter->second) {
           // Check the full inlined call stack against this one.
           // If we found and thus matched all frames on the call, include
@@ -1085,6 +1091,9 @@ readMemprof(Module &M, Function &F, IndexedInstrProfReader *MemProfReader,
             if (ClPrintMemProfMatchInfo || MemProfReportHintedSizes)
               FullStackId = computeFullStackId(AllocInfo->CallStack);
             auto AllocType = addCallStack(AllocTrie, AllocInfo, FullStackId);
+            TotalSize += AllocInfo->Info.getTotalSize();
+            if (AllocType == AllocationType::Cold)
+              TotalColdSize += AllocInfo->Info.getTotalSize();
             // Record information about the allocation if match info printing
             // was requested.
             if (ClPrintMemProfMatchInfo) {
@@ -1094,6 +1103,16 @@ readMemprof(Module &M, Function &F, IndexedInstrProfReader *MemProfReader,
             }
           }
         }
+        // If the threshold for the percent of cold bytes is less than 100%,
+        // and not all bytes are cold, see if we should still hint this
+        // allocation as cold without context sensitivity.
+        if (TotalColdSize < TotalSize && MinMatchedColdBytePercent < 100 &&
+            TotalColdSize * 100 >= MinMatchedColdBytePercent * TotalSize) {
+          AllocTrie.addSingleAllocTypeAttribute(CI, AllocationType::Cold,
+                                                "dominant");
+          continue;
+        }
+
         // We might not have matched any to the full inlined call stack.
         // But if we did, create and attach metadata, or a function attribute if
         // all contexts have identical profiled behavior.
diff --git a/llvm/test/Transforms/PGOProfile/memprof.ll b/llvm/test/Transforms/PGOProfile/memprof.ll
index f1b361de0fbba5..7e47c8ded4e4a7 100644
--- a/llvm/test/Transforms/PGOProfile/memprof.ll
+++ b/llvm/test/Transforms/PGOProfile/memprof.ll
@@ -64,7 +64,10 @@
 ; RUN: opt < %s -passes='pgo-instr-use,memprof-use<profile-filename=%t.pgomemprofdata>' -pgo-test-profile-file=%t.pgomemprofdata -pgo-warn-missing-function -S 2>&1 | FileCheck %s --check-prefixes=MEMPROF,ALL,PGO
 
 ;; Check that the total sizes are reported if requested.
-; RUN: opt < %s -passes='memprof-use<profile-filename=%t.memprofdata>' -pgo-warn-missing-function -S -memprof-report-hinted-sizes 2>&1 | FileCheck %s --check-prefixes=TOTALSIZES
+; RUN: opt < %s -passes='memprof-use<profile-filename=%t.memprofdata>' -pgo-warn-missing-function -S -memprof-report-hinted-sizes 2>&1 | FileCheck %s --check-prefixes=TOTALSIZESSINGLE,TOTALSIZES
+
+;; Check that we hint additional allocations with a threshold < 100%
+; RUN: opt < %s -passes='memprof-use<profile-filename=%t.memprofdata>' -pgo-warn-missing-function -S -memprof-report-hinted-sizes -memprof-matching-cold-threshold=60 2>&1 | FileCheck %s --check-prefixes=TOTALSIZESSINGLE,TOTALSIZESTHRESH60
 
 ;; Make sure we emit a random hotness seed if requested.
 ; RUN: llvm-profdata merge -memprof-random-hotness %S/Inputs/memprof.memprofraw --profiled-binary %S/Inputs/memprof.exe -o %t.memprofdatarand 2>&1 | FileCheck %s --check-prefix=RAND
@@ -348,8 +351,14 @@ for.end:                                          ; preds = %for.cond
 
 ;; For non-context sensitive allocations that get attributes we emit a message
 ;; with the full allocation context hash, type, and size in bytes.
-; TOTALSIZES: Total size for full allocation context hash 6792096022461663180 and single alloc type notcold: 10
-; TOTALSIZES: Total size for full allocation context hash 15737101490731057601 and single alloc type cold: 10
+; TOTALSIZESTHRESH60: Total size for full allocation context hash 8525406123785421946 and dominant alloc type cold: 10
+; TOTALSIZESTHRESH60: Total size for full allocation context hash 11714230664165068698 and dominant alloc type cold: 10
+; TOTALSIZESTHRESH60: Total size for full allocation context hash 5725971306423925017 and dominant alloc type cold: 10
+; TOTALSIZESTHRESH60: Total size for full allocation context hash 16342802530253093571 and dominant alloc type cold: 10
+; TOTALSIZESTHRESH60: Total size for full allocation context hash 18254812774972004394 and dominant alloc type cold: 10
+; TOTALSIZESTHRESH60: Total size for full allocation context hash 1093248920606587996 and dominant alloc type cold: 10
+; TOTALSIZESSINGLE: Total size for full allocation context hash 6792096022461663180 and single alloc type notcold: 10
+; TOTALSIZESSINGLE: Total size for full allocation context hash 15737101490731057601 and single alloc type cold: 10
 ;; For context sensitive allocations the full context hash and size in bytes
 ;; are in separate metadata nodes included on the MIB metadata.
 ; TOTALSIZES: !"cold", ![[CONTEXT1:[0-9]+]]}

``````````

</details>


https://github.com/llvm/llvm-project/pull/120301