[PseudoProbe] Use probe id as the base dwarf discriminator for callsites (#65685)

With `-fpseudo-probe-for-profiling`, the dwarf discriminator for a
callsite will be overwritten to pseudo probe related information for
that callsite. The probe information is encoded in a special format
(i.e., with all lowest three digits be one) in order to be distinguished
from regular dwarf discriminator. The special encoding format will be
decoded to zero by the regular discriminator logic. This means all
callsites would have a zero discriminator in both the sample profile and
the compiler, for classic AutoFDO. This is inconvenient in that no
decent classic AutoFDO can be generated from a pseudo probe build. I'm
mitigating the issue by allowing callsite probe id to be used as the
base dwarf discriminator for classic AutoFDO, since probe id is also
unique and can be used to differentiate callsites on the same source
line.

Author: htyu

llvm/include/llvm/IR/DebugInfoMetadata.h

@@ -22,6 +22,7 @@
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/Metadata.h"
+#include "llvm/IR/PseudoProbe.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Discriminator.h"
@@ -2075,6 +2076,14 @@ 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))
+      return PseudoProbeDwarfDiscriminator::extractProbeIndex(D);
+
     if (IsFSDiscriminator)
       return getMaskedDiscriminator(D, getBaseDiscriminatorBits());
     return getUnsignedFromPrefixEncoding(D);

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

@@ -106,6 +106,8 @@ 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/tools/llvm-profgen/inline-probe-afdo.test

@@ -0,0 +1,82 @@
+; RUN: llvm-profgen --format=text --use-dwarf-correlation --ignore-stack-samples --perfscript=%S/Inputs/cs-preinline-cost.perfscript --binary=%S/Inputs/cs-preinline-cost.perfbin --output %t
+; RUN: FileCheck %s --input-file %t
+
+; CHECK:     main:947937:0
+; CHECK-NEXT:  2: 545
+; CHECK-NEXT:  3: 545
+; CHECK-NEXT:  5: 545
+; CHECK-NEXT:  7: 0
+; CHECK-NEXT:  65496: 545
+; CHECK-NEXT:  3.7: _Z3fooi:915794
+; CHECK-NEXT:   1: 545
+; CHECK-NEXT:   5: 545
+; CHECK-NEXT:   6: 272
+; CHECK-NEXT:   10: 273
+; CHECK-NEXT:   11: 180
+; CHECK-NEXT:   12: 6965
+; CHECK-NEXT:   13: 6965
+; CHECK-NEXT:   14: 6965
+; CHECK-NEXT:   15: 6965
+; CHECK-NEXT:   20: 182
+; CHECK-NEXT:   21: 6958
+; CHECK-NEXT:   22: 6958
+; CHECK-NEXT:   23: 6958
+; CHECK-NEXT:   24: 6958
+; CHECK-NEXT:   29: 272
+; CHECK-NEXT:   65529: 182
+; CHECK-NEXT:  4.8: _Z3fooi:16338
+; CHECK-NEXT:   1: 272
+; CHECK-NEXT:   6: 545
+
+
+
+
+; binary is built with the source below using the following command line:
+;   clang -O3 -g -fpseudo-probe-for-profiling test.cpp
+;
+;#include <stdio.h>
+;
+;volatile int state = 9000;
+;
+;int foo(int x) {
+;    if (x == 0) {
+;        return 7;
+;    }
+;
+;    if ((x & 1) == 0) {
+;        state--;
+;        return 9;
+;    }
+;
+;    if (state > 5000) {
+;        while (state > 5000) {
+;               for (int i = 50; i >= 0; i--) {
+;                state *= 6;
+;                state /= 7;
+;                state -= 1;
+;            }
+;        }
+;    }
+;    else {
+;        while (state < 5000) {
+;            for (int i = 50; i >= 0; i--) {
+;                state *= 6;
+;                state /= 5;
+;                state += 1;
+;            }
+;        }
+;    }
+;
+;    return state;
+;}
+;
+;volatile int cnt = 10000000;//10000000;
+;int main() {
+;    int r = 0;
+;    for (int i = 0; i < cnt; i++) {
+;      r += foo(i);
+;      r -= foo(i & (~1));
+;      r += foo(0);
+;    }
+;    return r;
+;}