[PseudoProbe] Make probe discriminator compatible with dwarf base discriminator (#94506)

It's useful if the probe-based build can consume a dwarf based
profile(e.g. the profile transition), before there is a conflict for the
discriminator, this change tries to mitigate the issue by encoding the
dwarf base discriminator into the probe discriminator.
As the num of probe id(num of basic block and calls) starts from 1,
there are some unused space. We try to reuse some bit of the probe id.
The new encode rule is:
- Use a bit to [28:28] to indicate whether dwarf base discriminator is
encoded.(fortunately we can borrow this bit from the `PseudoProbeType`)
- If the bit is set, use [15:3] for probe id, [18:16] for dwarf base
discriminator. Otherwise, still use [18:3] for probe id.

Note that these doesn't affect the original probe id capacity, we still
prioritize probe id encoding, i.e. the base discriminator is not encoded
when probe id is bigger than [15:3].
 
Then adjust `getBaseDiscriminatorFromDiscriminator` to use the base
discriminator from the probe discriminator.

Author: wlei-llvm

llvm/include/llvm/IR/DebugInfoMetadata.h

@@ -2147,13 +2147,20 @@ class DILocation : public MDNode {
   static unsigned
   getBaseDiscriminatorFromDiscriminator(unsigned D,
                                         bool IsFSDiscriminator = false) {
-    // Return the probe id instead of zero for a pseudo probe discriminator.
-    // This should help differenciate callsites with same line numbers to
-    // achieve a decent AutoFDO profile under -fpseudo-probe-for-profiling,
-    // where the original callsite dwarf discriminator is overwritten by
-    // callsite probe information.
-    if (isPseudoProbeDiscriminator(D))
+    // Extract the dwarf base discriminator if it's encoded in the pseudo probe
+    // discriminator.
+    if (isPseudoProbeDiscriminator(D)) {
+      auto DwarfBaseDiscriminator =
+          PseudoProbeDwarfDiscriminator::extractDwarfBaseDiscriminator(D);
+      if (DwarfBaseDiscriminator)
+        return *DwarfBaseDiscriminator;
+      // Return the probe id instead of zero for a pseudo probe discriminator.
+      // This should help differenciate callsites with same line numbers to
+      // achieve a decent AutoFDO profile under -fpseudo-probe-for-profiling,
+      // where the original callsite dwarf discriminator is overwritten by
+      // callsite probe information.
       return PseudoProbeDwarfDiscriminator::extractProbeIndex(D);
+    }
 
     if (IsFSDiscriminator)
       return getMaskedDiscriminator(D, getBaseDiscriminatorBits());

llvm/include/llvm/IR/PseudoProbe.h

@@ -44,26 +44,51 @@ struct PseudoProbeDwarfDiscriminator {
   // 32-bit integer which is organized as:
   //  [2:0] - 0x7, this is reserved for regular discriminator,
   //          see DWARF discriminator encoding rule
-  //  [18:3] - probe id
+  //  if the [28:28] bit is zero:
+  //    [18:3] for probe id.
+  //  else:
+  //    [15:3] for probe id, [18:16] for dwarf base discriminator.
   //  [25:19] - probe distribution factor
-  //  [28:26] - probe type, see PseudoProbeType
-  //  [31:29] - reserved for probe attributes
-  static uint32_t packProbeData(uint32_t Index, uint32_t Type, uint32_t Flags,
-                                uint32_t Factor) {
+  //  [27:26] - probe type, see PseudoProbeType
+  //  [28:28] - indicates whether dwarf base discriminator is encoded.
+  //  [30:29] - reserved for probe attributes
+  static uint32_t
+  packProbeData(uint32_t Index, uint32_t Type, uint32_t Flags, uint32_t Factor,
+                std::optional<uint32_t> DwarfBaseDiscriminator) {
     assert(Index <= 0xFFFF && "Probe index too big to encode, exceeding 2^16");
-    assert(Type <= 0x7 && "Probe type too big to encode, exceeding 7");
+    assert(Type <= 0x3 && "Probe type too big to encode, exceeding 3");
     assert(Flags <= 0x7);
     assert(Factor <= 100 &&
            "Probe distribution factor too big to encode, exceeding 100");
-    return (Index << 3) | (Factor << 19) | (Type << 26) | 0x7;
+    uint32_t V = (Index << 3) | (Factor << 19) | (Type << 26) | 0x7;
+    // If both the probe id and dwarf base discriminator is small, the probe id
+    // space is shared with the dwarf base discriminator, this is to make the
+    // probe-based build compatible with the dwarf-based profile.
+    // Pack the dwarf base discriminator into [18:16] and set the [28:28] bit.
+    if (Index <= 0x1FFF && DwarfBaseDiscriminator &&
+        *DwarfBaseDiscriminator <= 0x7)
+      V |= (1 << 28) | (*DwarfBaseDiscriminator << 16);
+    return V;
   }
 
   static uint32_t extractProbeIndex(uint32_t Value) {
+    if (isDwarfBaseDiscriminatorEncoded(Value))
+      return (Value >> 3) & 0x1FFF;
     return (Value >> 3) & 0xFFFF;
   }
 
+  static std::optional<uint32_t> extractDwarfBaseDiscriminator(uint32_t Value) {
+    if (isDwarfBaseDiscriminatorEncoded(Value))
+      return (Value >> 16) & 0x7;
+    return std::nullopt;
+  }
+
+  static bool isDwarfBaseDiscriminatorEncoded(uint32_t Value) {
+    return Value & 0x10000000;
+  }
+
   static uint32_t extractProbeType(uint32_t Value) {
-    return (Value >> 26) & 0x7;
+    return (Value >> 26) & 0x3;
   }
 
   static uint32_t extractProbeAttributes(uint32_t Value) {

llvm/lib/IR/PseudoProbe.cpp

@@ -95,13 +95,16 @@ void setProbeDistributionFactor(Instruction &Inst, float Factor) {
             PseudoProbeDwarfDiscriminator::extractProbeType(Discriminator);
         auto Attr = PseudoProbeDwarfDiscriminator::extractProbeAttributes(
             Discriminator);
+        auto DwarfBaseDiscriminator =
+            PseudoProbeDwarfDiscriminator::extractDwarfBaseDiscriminator(
+                Discriminator);
         // Round small factors to 0 to avoid over-counting.
         uint32_t IntFactor =
             PseudoProbeDwarfDiscriminator::FullDistributionFactor;
         if (Factor < 1)
           IntFactor *= Factor;
         uint32_t V = PseudoProbeDwarfDiscriminator::packProbeData(
-            Index, Type, Attr, IntFactor);
+            Index, Type, Attr, IntFactor, DwarfBaseDiscriminator);
         DIL = DIL->cloneWithDiscriminator(V);
         Inst.setDebugLoc(DIL);
       }

llvm/lib/Transforms/IPO/SampleProfileProbe.cpp

@@ -431,8 +431,8 @@ void SampleProfileProber::instrumentOneFunc(Function &F, TargetMachine *TM) {
       // and type of a callsite probe. This gets rid of the dependency on
       // plumbing a customized metadata through the codegen pipeline.
       uint32_t V = PseudoProbeDwarfDiscriminator::packProbeData(
-          Index, Type, 0,
-          PseudoProbeDwarfDiscriminator::FullDistributionFactor);
+          Index, Type, 0, PseudoProbeDwarfDiscriminator::FullDistributionFactor,
+          DIL->getBaseDiscriminator());
       DIL = DIL->cloneWithDiscriminator(V);
       Call->setDebugLoc(DIL);
     }

llvm/test/Transforms/SampleProfile/pseudo-probe-discriminator.ll

@@ -64,8 +64,8 @@ attributes #1 = { "disable-tail-calls"="false" "less-precise-fpmad"="false" "fra
 
 
 ; PROBE: ![[CALL1]] = !DILocation(line: 4, column: 3, scope: ![[CALL1BLOCK:[0-9]+]])
-; PROBE: ![[CALL1BLOCK]] = !DILexicalBlockFile({{.*}} discriminator: 186646559)
+; PROBE: ![[CALL1BLOCK]] = !DILexicalBlockFile({{.*}} discriminator: 455147551)
 ; PROBE: ![[CALL2]] = !DILocation(line: 4, column: 9, scope: ![[CALL2BLOCK:[0-9]+]])
-; PROBE: ![[CALL2BLOCK]] = !DILexicalBlockFile({{.*}} discriminator: 186646567)
+; PROBE: ![[CALL2BLOCK]] = !DILexicalBlockFile({{.*}} discriminator: 455344167)
 ; PROBE: ![[INST]] = !DILocation(line: 4, column: 15, scope: ![[INSTBLOCK:[0-9]+]])
 ; PROBE: ![[INSTBLOCK]] = !DILexicalBlockFile({{.*}} discriminator: 4)

llvm/test/Transforms/SampleProfile/pseudo-probe-emit-inline.ll

@@ -42,13 +42,13 @@ define dso_local i32 @entry() !dbg !14 {
 ; CHECK-IL: ![[#SCOPE2:]] = distinct !DISubprogram(name: "foo"
 ; CHECK-IL: ![[#DL1]] = !DILocation(line: 3, column: 1,  scope: ![[#SCOPE1]], inlinedAt: ![[#INL1:]])
 ; CHECK-IL: ![[#INL1]] = distinct !DILocation(line: 7, column: 3, scope: ![[#BL1:]])
-;; A discriminator of 186646551 which is 0xb200017 in hexdecimal, stands for a direct call probe
+;; A discriminator of 455082007 which is 0x1b200017 in hexdecimal, stands for a direct call probe
 ;; with an index of 2 and a scale of 100%.
-; CHECK-IL: ![[#BL1]] = !DILexicalBlockFile(scope: ![[#SCOPE2]], file: !1, discriminator: 186646551)
+; CHECK-IL: ![[#BL1]] = !DILexicalBlockFile(scope: ![[#SCOPE2]], file: !1, discriminator: 455082007)
 ; CHECK-IL: ![[#SCOPE3:]] = distinct !DISubprogram(name: "entry"
 ; CHECK-IL: ![[#DL2]] = !DILocation(line: 7, column: 3,  scope: ![[#SCOPE2]], inlinedAt: ![[#INL2:]])
 ; CHECK-IL: ![[#INL2]] = distinct !DILocation(line: 11, column: 3, scope: ![[#BL2:]])
-; CHECK-IL: ![[#BL2]] = !DILexicalBlockFile(scope: ![[#SCOPE3]], file: !1, discriminator: 186646551)
+; CHECK-IL: ![[#BL2]] = !DILexicalBlockFile(scope: ![[#SCOPE3]], file: !1, discriminator: 455082007)
 ; CHECK-IL: ![[#DL3]] = !DILocation(line: 3, column: 1,  scope: ![[#SCOPE1]], inlinedAt: ![[#INL3:]])
 ; CHECK-IL: ![[#INL3]] = distinct !DILocation(line: 7, column: 3,  scope: ![[#BL1]], inlinedAt: ![[#INL2]])
 

llvm/test/Transforms/SampleProfile/pseudo-probe-emit.ll

@@ -84,13 +84,13 @@ entry:
 ; CHECK-IL: ![[#REALLINE]] = !DILocation(line: 2, scope: ![[#DISC0:]])
 ; CHECK-IL: ![[#DISC0]] = !DILexicalBlockFile(scope: ![[#FOO]], file: ![[#]], discriminator: 0)
 ; CHECK-IL: ![[#PROBE0]] = !DILocation(line: 2, column: 20, scope: ![[#SCOPE0:]])
-;; A discriminator of 67108887 which is 0x7200017 in hexdecimal, stands for a direct call probe
+;; A discriminator of 387973143 which is 0x17200017 in hexdecimal, stands for a direct call probe
 ;; with an index of 2.
-; CHECK-IL: ![[#SCOPE0]] = !DILexicalBlockFile(scope: ![[#]], file: ![[#]], discriminator: 119537687)
+; CHECK-IL: ![[#SCOPE0]] = !DILexicalBlockFile(scope: ![[#]], file: ![[#]], discriminator: 387973143)
 ; CHECK-IL: ![[#PROBE1]] = !DILocation(line: 0, scope: ![[#SCOPE1:]])
-;; A discriminator of 186646559 which is 0xb20001f in hexdecimal, stands for a direct call probe
+;; A discriminator of 455082015 which is 0x1b20001f in hexdecimal, stands for a direct call probe
 ;; with an index of 3.
-; CHECK-IL: ![[#SCOPE1]] = !DILexicalBlockFile(scope: ![[#]], file: ![[#]], discriminator: 186646559)
+; CHECK-IL: ![[#SCOPE1]] = !DILexicalBlockFile(scope: ![[#]], file: ![[#]], discriminator: 455082015)
 
 ; Check the generation of .pseudo_probe_desc section
 ; CHECK-ASM: .section .pseudo_probe_desc,"G",@progbits,.pseudo_probe_desc_foo,comdat

llvm/test/Transforms/SampleProfile/pseudo-probe-inline.ll

@@ -106,8 +106,6 @@ if.end:
 ;YAML-NEXT:    - Line:            '1'
 ;YAML-NEXT:    - String:          ':'
 ;YAML-NEXT:    - Column:          '11'
-;YAML-NEXT:    - String:          .
-;YAML-NEXT:    - Disc:            '2'
 ;YAML-NEXT:    - String:          ';'
 ;YAML-NEXT:  ...
 ;YAML:  --- !Analysis

llvm/test/Transforms/SampleProfile/pseudo-probe-profile.ll

@@ -40,14 +40,14 @@ attributes #0 = {"use-sample-profile"}
 
 ; CHECK: ![[PD1]] = !{!"branch_weights", i32 8, i32 7}
 ; CHECK: ![[#PROBE1]] = !DILocation(line: 0, scope: ![[#SCOPE1:]])
-;; A discriminator of 119537695 which is 0x720001f in hexdecimal, stands for an indirect call probe
+;; A discriminator of 387973151 which is 0x1720001f in hexdecimal, stands for an indirect call probe
 ;; with an index of 3.
-; CHECK: ![[#SCOPE1]] = !DILexicalBlockFile(scope: ![[#]], file: ![[#]], discriminator: 119537695)
+; CHECK: ![[#SCOPE1]] = !DILexicalBlockFile(scope: ![[#]], file: ![[#]], discriminator: 387973151)
 ; CHECK: ![[PROF1]] = !{!"VP", i32 0, i64 7, i64 9191153033785521275, i64 5, i64 -1069303473483922844, i64 2}
-;; A discriminator of 119537711 which is 0x720002f in hexdecimal, stands for an indirect call probe
+;; A discriminator of 387973167 which is 0x1720002f in hexdecimal, stands for an indirect call probe
 ;; with an index of 5.
 ; CHECK: ![[#PROBE2]] = !DILocation(line: 0, scope: ![[#SCOPE2:]])
-; CHECK: ![[#SCOPE2]] = !DILexicalBlockFile(scope: ![[#]], file: ![[#]], discriminator: 119537711)
+; CHECK: ![[#SCOPE2]] = !DILexicalBlockFile(scope: ![[#]], file: ![[#]], discriminator: 387973167)
 ; CHECK: ![[PROF2]] = !{!"VP", i32 0, i64 6, i64 -1069303473483922844, i64 4, i64 9191153033785521275, i64 2}
 
 !llvm.module.flags = !{!9, !10}

llvm/test/Transforms/SampleProfile/pseudo-probe-verify.ll

@@ -54,10 +54,10 @@ bb24:
   ret void
 }
 
-;; A discriminator of 186646583 which is 0xb200037 in hexdecimal, stands for a direct call probe
+;; A discriminator of 455082031 which is 0x1b200037 in hexdecimal, stands for a direct call probe
 ;; with an index of 6 and a scale of -1%.
 ; CHECK: ![[#PROBE6]] = !DILocation(line: 2, column: 20, scope: ![[#SCOPE:]])
-; CHECK: ![[#SCOPE]] = !DILexicalBlockFile(scope: ![[#]], file: ![[#]], discriminator: 186646575)
+; CHECK: ![[#SCOPE]] = !DILexicalBlockFile(scope: ![[#]], file: ![[#]], discriminator: 455082031)
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!9, !10}