[llvm] d4d6b9a - [FS-AFDO] Clean up non-zero discriminator for pseudo probes at the first FS discriminator pass.

[Hongtao Yu via llvm-commits]

Author: Hongtao Yu
Date: 2023-05-16T21:35:17-07:00
New Revision: d4d6b9a142f0017b4d5668155fbbe045c838b8a6

URL: https://github.com/llvm/llvm-project/commit/d4d6b9a142f0017b4d5668155fbbe045c838b8a6
DIFF: https://github.com/llvm/llvm-project/commit/d4d6b9a142f0017b4d5668155fbbe045c838b8a6.diff

LOG: [FS-AFDO] Clean up non-zero discriminator for pseudo probes at the first FS discriminator pass.

The dwarf discriminator field for pseudo probes is not supposed to be used until the first FS discriminator pass. Unfortunately there are always corner cases that accidientally set this field. For example, the inliner could set this field for an inlined instruction if the instruction does not come with any debug information. While fixing all such spots is possible, but for future-proff I'd like to enforce a general cleanup before assigning probes any FS discriminator.

Reviewed By: wenlei

Differential Revision: https://reviews.llvm.org/D150741

Added: 
    

Modified: 
    llvm/include/llvm/CodeGen/MIRFSDiscriminator.h
    llvm/lib/CodeGen/MIRFSDiscriminator.cpp
    llvm/test/CodeGen/X86/fsafdo_probe.ll

Removed: 
    


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diff  --git a/llvm/include/llvm/CodeGen/MIRFSDiscriminator.h b/llvm/include/llvm/CodeGen/MIRFSDiscriminator.h
index 1ab55a7d4f0ca..da943268dac87 100644
--- a/llvm/include/llvm/CodeGen/MIRFSDiscriminator.h
+++ b/llvm/include/llvm/CodeGen/MIRFSDiscriminator.h
@@ -31,6 +31,7 @@ class MachineFunction;
 using namespace sampleprof;
 class MIRAddFSDiscriminators : public MachineFunctionPass {
   MachineFunction *MF = nullptr;
+  FSDiscriminatorPass Pass;
   unsigned LowBit;
   unsigned HighBit;
 
@@ -38,7 +39,7 @@ class MIRAddFSDiscriminators : public MachineFunctionPass {
   static char ID;
   /// PassNum is the sequence number this pass is called, start from 1.
   MIRAddFSDiscriminators(FSDiscriminatorPass P = FSDiscriminatorPass::Pass1)
-      : MachineFunctionPass(ID) {
+      : MachineFunctionPass(ID), Pass(P) {
     LowBit = getFSPassBitBegin(P);
     HighBit = getFSPassBitEnd(P);
     assert(LowBit < HighBit && "HighBit needs to be greater than Lowbit");

diff  --git a/llvm/lib/CodeGen/MIRFSDiscriminator.cpp b/llvm/lib/CodeGen/MIRFSDiscriminator.cpp
index 6f985df74c4de..bdafe216e8f11 100644
--- a/llvm/lib/CodeGen/MIRFSDiscriminator.cpp
+++ b/llvm/lib/CodeGen/MIRFSDiscriminator.cpp
@@ -150,6 +150,12 @@ bool MIRAddFSDiscriminators::runOnMachineFunction(MachineFunction &MF) {
       if (LineNo == 0)
         continue;
       unsigned Discriminator = DIL->getDiscriminator();
+      // Clean up discriminators for pseudo probes at the first FS discriminator
+      // pass as their discriminators should not ever be used.
+      if ((Pass == FSDiscriminatorPass::Pass1) && I.isPseudoProbe()) {
+        Discriminator = 0;
+        I.setDebugLoc(DIL->cloneWithDiscriminator(0));
+      }
       uint64_t CallStackHashVal = 0;
       if (ImprovedFSDiscriminator)
         CallStackHashVal = getCallStackHash(DIL);

diff  --git a/llvm/test/CodeGen/X86/fsafdo_probe.ll b/llvm/test/CodeGen/X86/fsafdo_probe.ll
index bc19a297dc428..fa91670306ba1 100644
--- a/llvm/test/CodeGen/X86/fsafdo_probe.ll
+++ b/llvm/test/CodeGen/X86/fsafdo_probe.ll
@@ -65,7 +65,8 @@ attributes #0 = { inaccessiblememonly nocallback nofree nosync nounwind willretu
 !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)
+;; The discriminator with value 2 is to test that it can be cleaned up by the first FS discriminator pass.
+!9 = !DILexicalBlockFile(scope: !6, file: !1, discriminator: 2)
 !10 = !DILocation(line: 7, column: 3, scope: !9)
 !11 = !DILocation(line: 9, column: 5, scope: !9)
 !12 = !DILocation(line: 14, column: 3, scope: !6)