[FS-AFDO] Assign discriminators to pseudo probes

This is the first change for FS-AFDO integration with CSSPGO. There are more patches coming.

With pseudo probes, we do not assign FS discriminators to any other instructions since we will be using only probes for profile correlation.

Also call instructions are excluded since their dwarf discriminators are used for other purposes, i.e, storing probe ids. Since they are not getting a FS discriminator, they will also be excluded from MIR profile loading. The corresponding changes will be in the subsequent patches.

Reviewed By: wenlei

Differential Revision: https://reviews.llvm.org/D147286

diff --git a/llvm/lib/CodeGen/MIRFSDiscriminator.cpp b/llvm/lib/CodeGen/MIRFSDiscriminator.cpp
index e2166a4..6f985df 100644 (file)
--- a/llvm/lib/CodeGen/MIRFSDiscriminator.cpp
+++ b/llvm/lib/CodeGen/MIRFSDiscriminator.cpp
@@ -18,6 +18,8 @@
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/Function.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PseudoProbe.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
@@ -92,7 +94,11 @@ static uint64_t getCallStackHash(const DILocation *DIL) {
 bool MIRAddFSDiscriminators::runOnMachineFunction(MachineFunction &MF) {
   if (!EnableFSDiscriminator)
     return false;
-  if (!MF.getFunction().shouldEmitDebugInfoForProfiling())
+
+  bool HasPseudoProbe = MF.getFunction().getParent()->getNamedMetadata(
+      PseudoProbeDescMetadataName);
+
+  if (!HasPseudoProbe && !MF.getFunction().shouldEmitDebugInfoForProfiling())
     return false;
 
   bool Changed = false;
@@ -125,13 +131,22 @@ bool MIRAddFSDiscriminators::runOnMachineFunction(MachineFunction &MF) {
 
   for (MachineBasicBlock &BB : MF) {
     for (MachineInstr &I : BB) {
-      if (ImprovedFSDiscriminator && I.isMetaInstruction()) {
+      if (HasPseudoProbe) {
+        // Only assign discriminators to pseudo probe instructions. Call
+        // instructions are excluded since their dwarf discriminators are used
+        // for other purposes, i.e, storing probe ids.
+        if (!I.isPseudoProbe())
+          continue;
+      } else if (ImprovedFSDiscriminator && I.isMetaInstruction()) {
         continue;
       }
       const DILocation *DIL = I.getDebugLoc().get();
       if (!DIL)
         continue;
-      unsigned LineNo = DIL->getLine();
+
+      // Use the id of pseudo probe to compute the discriminator.
+      unsigned LineNo =
+          I.isPseudoProbe() ? I.getOperand(1).getImm() : DIL->getLine();
       if (LineNo == 0)
         continue;
       unsigned Discriminator = DIL->getDiscriminator();

diff --git a/llvm/test/CodeGen/X86/fsafdo_probe.ll b/llvm/test/CodeGen/X86/fsafdo_probe.ll
new file mode 100644 (file)
index 0000000..bc19a29
--- /dev/null
+++ b/llvm/test/CodeGen/X86/fsafdo_probe.ll
@@ -0,0 +1,72 @@
+; REQUIRES: x86_64-linux
+; REQUIRES: asserts
+; RUN: llc -enable-fs-discriminator -improved-fs-discriminator=false --debug-only=mirfs-discriminators  < %s  -o - 2>&1 | FileCheck %s --check-prefixes=V0
+; RUN: llc -enable-fs-discriminator -improved-fs-discriminator=true --debug-only=mirfs-discriminators  < %s  -o - 2>&1 | FileCheck %s --check-prefixes=V1
+
+; Check that fs-afdo discriminators are generated.
+; V0: foo.c:7:3: add FS discriminator, from 0 -> 11264
+; V0: foo.c:9:5: add FS discriminator, from 0 -> 11264
+; V0: Num of FS Discriminators: 2
+
+; V1: foo.c:7:3: add FS discriminator, from 0 -> 256
+; V1: foo.c:9:5: add FS discriminator, from 0 -> 256
+; V1: Num of FS Discriminators: 2
+
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.Node = type { ptr }
+
+define i32 @foo(ptr readonly %node, ptr readnone %root) !dbg !6  {
+entry:
+  call void @llvm.pseudoprobe(i64 6699318081062747564, i64 1, i32 0, i64 -1), !dbg !8
+  %cmp = icmp eq ptr %node, %root, !dbg !8
+  br i1 %cmp, label %while.end4, label %while.cond1.preheader.lr.ph, !dbg !10
+
+while.cond1.preheader.lr.ph:
+  %tobool = icmp eq ptr %node, null
+  call void @llvm.pseudoprobe(i64 6699318081062747564, i64 2, i32 0, i64 -1), !dbg !11
+  br i1 %tobool, label %while.cond1.preheader.us.preheader, label %while.body2.preheader, !dbg !11
+
+while.body2.preheader:
+  call void @llvm.pseudoprobe(i64 6699318081062747564, i64 2, i32 0, i64 -1), !dbg !11
+  br label %while.body2, !dbg !11
+
+while.cond1.preheader.us.preheader:
+  call void @llvm.pseudoprobe(i64 6699318081062747564, i64 3, i32 0, i64 -1), !dbg !10
+  br label %while.cond1.preheader.us, !dbg !10
+
+while.cond1.preheader.us:
+  call void @llvm.pseudoprobe(i64 6699318081062747564, i64 3, i32 0, i64 -1), !dbg !10
+  br label %while.cond1.preheader.us, !dbg !10
+
+while.body2:
+  call void @llvm.pseudoprobe(i64 6699318081062747564, i64 2, i32 0, i64 -1), !dbg !11
+  br label %while.body2, !dbg !11
+
+while.end4:
+  call void @llvm.pseudoprobe(i64 6699318081062747564, i64 4, i32 0, i64 -1), !dbg !12
+  ret i32 0, !dbg !12
+}
+
+declare void @llvm.pseudoprobe(i64, i64, i32, i64) #0
+
+attributes #0 = { inaccessiblememonly nocallback nofree nosync nounwind willreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.pseudo_probe_desc = !{!13}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, isOptimized: true, debugInfoForProfiling: true, emissionKind: LineTablesOnly)
+!1 = !DIFile(filename: "foo.c", directory: "b/")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{}
+!6 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 5, type: !7, isLocal: false, isDefinition: true, scopeLine: 5, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !2)
+!7 = !DISubroutineType(types: !2)
+!8 = !DILocation(line: 7, column: 15, scope: !9)
+!9 = !DILexicalBlockFile(scope: !6, file: !1, discriminator: 0)
+!10 = !DILocation(line: 7, column: 3, scope: !9)
+!11 = !DILocation(line: 9, column: 5, scope: !9)
+!12 = !DILocation(line: 14, column: 3, scope: !6)
+!13 = !{i64 6699318081062747564, i64 138464321060, !"foo"}