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

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 llvm#141164 for use by MemProf.

Author: snehasish

llvm/lib/Analysis/IndirectCallPromotionAnalysis.cpp

@@ -31,12 +31,18 @@ static cl::opt<unsigned> ICPRemainingPercentThreshold(
 
 // The percent threshold for the direct-call target (this call site vs the
 // total call count) for it to be considered as the promotion target.
-static cl::opt<unsigned>
+static cl::opt<uint64_t>
     ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5),
                              cl::Hidden,
                              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;
 }
 

llvm/test/Transforms/PGOProfile/indirect_call_promotion.ll

@@ -1,6 +1,10 @@
 ; 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-15
+; 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-10
 
 ; 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 +16,16 @@
 ; 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-15: remark: <unknown>:0:0: Promote indirect call to func4 with count 1030 out of 1600
+; MIN-COUNT-15: remark: <unknown>:0:0: Promote indirect call to func2 with count 410 out of 570
+; MIN-COUNT-15: remark: <unknown>:0:0: Promote indirect call to func3 with count 150 out of 160
+; MIN-COUNT-15-NOT: remark: <unknown>:0:0: Promote indirect call to func1
+
+; MIN-COUNT-10: remark: <unknown>:0:0: Promote indirect call to func4 with count 1030 out of 1600
+; MIN-COUNT-10: remark: <unknown>:0:0: Promote indirect call to func2 with count 410 out of 570
+; MIN-COUNT-10: remark: <unknown>:0:0: Promote indirect call to func3 with count 150 out of 160
+; MIN-COUNT-10: 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"