[Test + comment] Add a regression test to guard the 0 hot-caller threshold, and add comment near the threshold definition.

[tejohnson]

Thanks! Couple minor suggestions.

llvm/lib/Passes/PassBuilderPipelines.cpp

716

Nit here and in second instance of this comment: I think these lines are well under 80 chars? Can you change the line wrapping to make better use of the full line?

721

Not sure the test reference is needed or wanted here. I would remove that and if anything point to the place in the inline cost handling that shows how we can end up with a negative cost. But probably not necessary - in which case I would combine this with your earlier note "as much as possible" since I think this is the explanation for that aside? I.e. something like "as much as possible as the cost of a function could be negative". Or "as much as possible [1]" and later "[1] Note the cost of a function could be below zero."

llvm/test/Other/new-pm-thinlto-prelink-samplepgo-inline-threshold.ll

8

I think first "is" should be removed (from "is basic block is cold").

[mingmingl]

thanks!

llvm/lib/Passes/PassBuilderPipelines.cpp

721

Done by revising to "as much as possible [1]" and later "[1] Note the cost of a function could be below zero." (here and below)

[mingmingl]

remove new lines added by editor

[mingmingl]

Truly removed newlines..

[tejohnson]

lgtm

[mingmingl]

It seems that reviews.llvm.org has stopped tracking new origin/main commits and failed to auto close a differential when a commit with Differential Revision: is pushed to origin/main.

Close this manually.

llvm/lib/Passes/PassBuilderPipelines.cpp

 static InlineParams getInlineParamsFromOptLevel(OptimizationLevel Level) {
   return getInlineParams(Level.getSpeedupLevel(), Level.getSizeLevel());
 }
 
 ModuleInlinerWrapperPass
 PassBuilder::buildInlinerPipeline(OptimizationLevel Level,
                                   ThinOrFullLTOPhase Phase) {
   InlineParams IP = getInlineParamsFromOptLevel(Level);
+  // For PreLinkThinLTO + SamplePGO, set hot-caller threshold to 0 to
+  // disable hot callsite inline (as much as possible [1]) because it makes
+  // profile annotation in the backend inaccurate.
+  //
+  // [1] Note the cost of a function could be below zero due to erased
+  // prologue / epilogue.
   if (Phase == ThinOrFullLTOPhase::ThinLTOPreLink && PGOOpt &&
       PGOOpt->Action == PGOOptions::SampleUse)
     IP.HotCallSiteThreshold = 0;
 
   if (PGOOpt)
     IP.EnableDeferral = EnablePGOInlineDeferral;
 
   ModuleInlinerWrapperPass MIWP(IP, PerformMandatoryInliningsFirst,

 }
 
 ModulePassManager
 PassBuilder::buildModuleInlinerPipeline(OptimizationLevel Level,
                                         ThinOrFullLTOPhase Phase) {
   ModulePassManager MPM;
 
   InlineParams IP = getInlineParamsFromOptLevel(Level);
+  // For PreLinkThinLTO + SamplePGO, set hot-caller threshold to 0 to
+  // disable hot callsite inline (as much as possible [1]) because it makes
+  // profile annotation in the backend inaccurate.
+  //
+  // [1] Note the cost of a function could be below zero due to erased
+  // prologue / epilogue.
   if (Phase == ThinOrFullLTOPhase::ThinLTOPreLink && PGOOpt &&
       PGOOpt->Action == PGOOptions::SampleUse)
     IP.HotCallSiteThreshold = 0;
 
   if (PGOOpt)
     IP.EnableDeferral = EnablePGOInlineDeferral;
 
   // The inline deferral logic is used to avoid losing some

llvm/test/Other/Inputs/new-pm-thinlto-prelink-samplepgo-inline-threshold.prof

+_Z3sumii:105580:5279
+ 0: 5279
+ 1: 5279
+ 2: 5279
+_Z4sum1ii:105580:5279
+ 0: 5279
+ 1: 5279
+ 2: 5279
+main:225715:0
+ 2.1: 5553
+ 3: 4522
+ # This indicates that at line 3 of this function, the 'then' branch
+ # of the conditional is taken (discriminator '1').
+ 3.1: 5752 _Z3sumii:5860
+ 4: 20 _Z4sum1ii:20
+ 4.1: 11504 _Z4sum1ii:11720

llvm/test/Other/new-pm-thinlto-prelink-samplepgo-inline-threshold.ll

+; Tests that hot callsite threshold is set to 0 artifically for thinlto-prelink pipeline.
+;
+; Function `sum` is annotated with inline cost -1 and function `sum1` is
+; annotated with inline cost 0, by function attribute `function-inline-cost`.
+;
+; `if.then` basic block is hot so the callsite threshold is set to 0.
+; `while.body.split` basic block is cold so threshold is calculated using
+; the rest of default heuristics, which should be sufficient to inline a
+; function with 0 cost.
+
+; RUN: opt < %s -pass-remarks=inline -pass-remarks-missed=inline -passes='thinlto-pre-link<O2>' -pgo-kind=pgo-sample-use-pipeline -sample-profile-file=%S/Inputs/new-pm-thinlto-prelink-samplepgo-inline-threshold.prof -S | FileCheck %s
+
+; RUN: opt < %s -pass-remarks=inline -pass-remarks-missed=inline -passes='thinlto-pre-link<O2>' -pgo-kind=pgo-sample-use-pipeline -sample-profile-file=%S/Inputs/new-pm-thinlto-prelink-samplepgo-inline-threshold.prof -S 2>&1 | FileCheck %s -check-prefix=REMARK
+
+; Original C++ test case
+;
+; #include <stdio.h>
+
+; int sum(int x, int y) { return x + y; }
+
+; int sum1(int x, int y) { return x + y; }
+
+; int main() {
+;   int s, i = 0;
+;   while (i++ < 20000 * 20000) {
+;     if (i != 100) s = sum(i, s);
+;     s = sum1(i, s);
+;   }
+;   printf("sum is %d\n", s);
+;   return 0;
+; }
+;
+
+; REMARK: test.cc:14:9: '_Z4sum1ii' inlined into 'main' with (cost=0, threshold=45) at callsite main:4:9;
+; REMARK: test.cc:13:23: '_Z3sumii' inlined into 'main' with (cost=-1, threshold=0) at callsite main:3:23.2;
+; REMARK: test.cc:14:9: '_Z4sum1ii' not inlined into 'main' because too costly to inline (cost=0, threshold=0)
+
+; ModuleID = 'test.cc'
+source_filename = "test.cc"
+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"
+
+@.str = constant [11 x i8] c"sum is %d\0A\00", align 1
+
+define i32 @_Z3sumii(i32 %x, i32 %y) "function-inline-cost"="-1" #0 !dbg !7 {
+entry:
+  %add = add nsw i32 %y, %x, !dbg !10
+  ret i32 %add, !dbg !11
+}
+
+define i32 @_Z4sum1ii(i32 %x, i32 %y) "function-inline-cost"="0" #0 !dbg !12 {
+entry:
+  %add = add nsw i32 %y, %x, !dbg !13
+  ret i32 %add, !dbg !14
+}
+
+define i32 @main() #0 !dbg !15 {
+entry:
+  br label %while.body, !dbg !16
+
+while.body:                                       ; preds = %entry, %if.end
+  %inc14 = phi i32 [ 1, %entry ], [ %inc, %if.end ]
+  %s.013 = phi i32 [ undef, %entry ], [ %phi.call, %if.end ]
+  %cmp1.not = icmp eq i32 %inc14, 100, !dbg !17
+  br i1 %cmp1.not, label %while.body.split, label %if.then, !dbg !18
+
+while.body.split:                                 ; preds = %while.body
+; CHECK-NOT: call noundef i32 @_Z4sum1ii
+  %call211 = call noundef i32 @_Z4sum1ii(i32 100, i32 %s.013), !dbg !19
+  br label %if.end, !dbg !18
+
+if.then:                                          ; preds = %while.body
+; CHECK-NOT: call i32 @_Z3sumii
+; CHECK: call i32 @_Z4sum1ii
+  %call = call i32 @_Z3sumii(i32 %inc14, i32 %s.013), !dbg !20
+  %call212 = call i32 @_Z4sum1ii(i32 %inc14, i32 %call), !dbg !19
+  br label %if.end, !dbg !21
+
+if.end:                                           ; preds = %while.body.split, %if.then
+  %phi.call = phi i32 [ %call211, %while.body.split ], [ %call212, %if.then ], !dbg !19
+  %inc = add i32 %inc14, 1, !dbg !22
+  %exitcond.not = icmp eq i32 %inc, 400000001, !dbg !23
+  br i1 %exitcond.not, label %while.end, label %while.body, !dbg !16, !llvm.loop !24
+
+while.end:                                        ; preds = %if.end
+  %call3 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([11 x i8], [11 x i8]* @.str, i64 0, i64 0), i32 %phi.call), !dbg !27
+  ret i32 0, !dbg !28
+}
+
+declare i32 @printf(i8* nocapture noundef readonly, ...)
+
+attributes #0 = {"use-sample-profile"}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 14.0.0 (https://github.com/llvm/llvm-project.git 329fda39c507e8740978d10458451dcdb21563be)", isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cc", directory: "", checksumkind: CSK_MD5, checksum: "e8c44edbdcc2c41f9f891ac2b2ddd591")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!7 = distinct !DISubprogram(name: "sum", scope: !1, file: !1, line: 6, type: !8, scopeLine: 6, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !9)
+!8 = !DISubroutineType(types: !9)
+!9 = !{}
+!10 = !DILocation(line: 6, column: 60, scope: !7)
+!11 = !DILocation(line: 6, column: 51, scope: !7)
+!12 = distinct !DISubprogram(name: "sum1", scope: !1, file: !1, line: 8, type: !8, scopeLine: 8, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !9)
+!13 = !DILocation(line: 8, column: 61, scope: !12)
+!14 = !DILocation(line: 8, column: 52, scope: !12)
+!15 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 10, type: !8, scopeLine: 10, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !9)
+!16 = !DILocation(line: 12, column: 3, scope: !15)
+!17 = !DILocation(line: 13, column: 11, scope: !15)
+!18 = !DILocation(line: 13, column: 9, scope: !15)
+!19 = !DILocation(line: 14, column: 9, scope: !15)
+!20 = !DILocation(line: 13, column: 23, scope: !15)
+!21 = !DILocation(line: 13, column: 19, scope: !15)
+!22 = !DILocation(line: 12, column: 11, scope: !15)
+!23 = !DILocation(line: 12, column: 14, scope: !15)
+!24 = distinct !{!24, !16, !25, !26}
+!25 = !DILocation(line: 15, column: 3, scope: !15)
+!26 = !{!"llvm.loop.mustprogress"}
+!27 = !DILocation(line: 16, column: 3, scope: !15)
+!28 = !DILocation(line: 17, column: 3, scope: !15)