[llvm] Add minimum count threshold for indirect call promotion (PR #145282)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Snehasish Kumar (snehasish)

<details>
<summary>Changes</summary>

Allow users to set the minimum absolute count for indirect call promotion. This is primarily meant to be control indirect call promotion for synthetic vp metadata introduced in #<!-- -->141164 for use by MemProf.

---
Full diff: https://github.com/llvm/llvm-project/pull/145282.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/IndirectCallPromotionAnalysis.cpp (+8-1) 
- (modified) llvm/test/Transforms/PGOProfile/indirect_call_promotion.ll (+21) 


``````````diff
diff --git a/llvm/lib/Analysis/IndirectCallPromotionAnalysis.cpp b/llvm/lib/Analysis/IndirectCallPromotionAnalysis.cpp
index 90065e053b629..861dc0d364b84 100644
--- a/llvm/lib/Analysis/IndirectCallPromotionAnalysis.cpp
+++ b/llvm/lib/Analysis/IndirectCallPromotionAnalysis.cpp
@@ -37,6 +37,12 @@ static cl::opt<unsigned>
                              cl::desc("The percentage threshold against total "
                                       "count for the promotion"));
 
+// Set the minimum absolute count threshold for indirect call promotion.
+// Candidates with counts below this threshold will not be promoted.
+static cl::opt<unsigned> ICPMinimumCountThreshold(
+    "icp-minimum-count-threshold", cl::init(0), cl::Hidden,
+    cl::desc("Minimum absolute count for promotion candidate"));
+
 // Set the maximum number of targets to promote for a single indirect-call
 // callsite.
 static cl::opt<unsigned>
@@ -51,7 +57,8 @@ cl::opt<unsigned> MaxNumVTableAnnotations(
 bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
                                                    uint64_t TotalCount,
                                                    uint64_t RemainingCount) {
-  return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
+  return Count >= ICPMinimumCountThreshold &&
+         Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
          Count * 100 >= ICPTotalPercentThreshold * TotalCount;
 }
 
diff --git a/llvm/test/Transforms/PGOProfile/indirect_call_promotion.ll b/llvm/test/Transforms/PGOProfile/indirect_call_promotion.ll
index 3b0e3250cd6df..7f1fea9d1386a 100644
--- a/llvm/test/Transforms/PGOProfile/indirect_call_promotion.ll
+++ b/llvm/test/Transforms/PGOProfile/indirect_call_promotion.ll
@@ -1,6 +1,12 @@
 ; RUN: opt < %s -passes=pgo-icall-prom -S -icp-total-percent-threshold=50 | FileCheck %s --check-prefix=ICALL-PROM
 ; RUN: opt < %s -passes=pgo-icall-prom -S -pass-remarks=pgo-icall-prom -icp-remaining-percent-threshold=0 -icp-total-percent-threshold=0 -icp-max-prom=4 2>&1 | FileCheck %s --check-prefix=PASS-REMARK
 ; RUN: opt < %s -passes=pgo-icall-prom -S -pass-remarks=pgo-icall-prom -icp-remaining-percent-threshold=0 -icp-total-percent-threshold=20 -icp-max-prom=4 2>&1 | FileCheck %s --check-prefix=PASS2-REMARK
+; Test minimum count threshold - should prevent func1 promotion (count 10 < threshold 15)
+; RUN: opt < %s -passes=pgo-icall-prom -S -pass-remarks=pgo-icall-prom -icp-minimum-count-threshold=15 -icp-remaining-percent-threshold=0 -icp-total-percent-threshold=0 -icp-max-prom=4 2>&1 | FileCheck %s --check-prefix=MIN-COUNT-BLOCK
+; Test minimum count threshold - should allow func4 promotion (count 1030 > threshold 15) 
+; RUN: opt < %s -passes=pgo-icall-prom -S -pass-remarks=pgo-icall-prom -icp-minimum-count-threshold=15 -icp-remaining-percent-threshold=0 -icp-total-percent-threshold=0 -icp-max-prom=4 2>&1 | FileCheck %s --check-prefix=MIN-COUNT-ALLOW
+; Test edge case - threshold exactly at count value
+; RUN: opt < %s -passes=pgo-icall-prom -S -pass-remarks=pgo-icall-prom -icp-minimum-count-threshold=10 -icp-remaining-percent-threshold=0 -icp-total-percent-threshold=0 -icp-max-prom=4 2>&1 | FileCheck %s --check-prefix=MIN-COUNT-EDGE
 
 ; PASS-REMARK: remark: <unknown>:0:0: Promote indirect call to func4 with count 1030 out of 1600
 ; PASS-REMARK: remark: <unknown>:0:0: Promote indirect call to func2 with count 410 out of 570
@@ -12,6 +18,21 @@
 ; PASS2-REMARK-NOT: remark: <unknown>:0:0: Promote indirect call to func3
 ; PASS2-REMARK-NOT: remark: <unknown>:0:0: Promote indirect call to func1
 
+; MIN-COUNT-BLOCK: remark: <unknown>:0:0: Promote indirect call to func4 with count 1030 out of 1600
+; MIN-COUNT-BLOCK: remark: <unknown>:0:0: Promote indirect call to func2 with count 410 out of 570
+; MIN-COUNT-BLOCK: remark: <unknown>:0:0: Promote indirect call to func3 with count 150 out of 160
+; MIN-COUNT-BLOCK-NOT: remark: <unknown>:0:0: Promote indirect call to func1
+
+; MIN-COUNT-ALLOW: remark: <unknown>:0:0: Promote indirect call to func4 with count 1030 out of 1600
+; MIN-COUNT-ALLOW: remark: <unknown>:0:0: Promote indirect call to func2 with count 410 out of 570
+; MIN-COUNT-ALLOW: remark: <unknown>:0:0: Promote indirect call to func3 with count 150 out of 160
+; MIN-COUNT-ALLOW-NOT: remark: <unknown>:0:0: Promote indirect call to func1
+
+; MIN-COUNT-EDGE: remark: <unknown>:0:0: Promote indirect call to func4 with count 1030 out of 1600
+; MIN-COUNT-EDGE: remark: <unknown>:0:0: Promote indirect call to func2 with count 410 out of 570
+; MIN-COUNT-EDGE: remark: <unknown>:0:0: Promote indirect call to func3 with count 150 out of 160
+; MIN-COUNT-EDGE: remark: <unknown>:0:0: Promote indirect call to func1 with count 10 out of 10
+
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/145282