[Sample-PGO] Emit FS discriminators only when -fdebug-info-for-profiling is set

[xur]

Summary

IR level addDiscriminator pass is guarded by DebugInfoForProfiling (set by option -fdebug-info-for-profiling).

This patch syncs the logic for the MIR and IR level implementations.

[wenlei]

lgtm, thanks.

[xur]

Another way to do this is to check PGOOpt->DebugInfoForProfiling in TargetPassConfig before adding the passes.
That would be the same as IR level addDiscriminator.

But since PGOOpt might not be set for some invocations (like in the unit tests). I would need to introduce
an extra internal option.

I think the change is this patch is simpler.

llvm/lib/CodeGen/MIRFSDiscriminator.cpp

 // Traverse the CFG and assign FD discriminators. If two instructions
 // have the same lineno and discriminator, but residing in different BBs,
 // the latter instruction will get a new discriminator value. The new
 // discriminator keeps the existing discriminator value but sets new bits
 // b/w LowBit and HighBit.
 bool MIRAddFSDiscriminators::runOnMachineFunction(MachineFunction &MF) {
   if (!EnableFSDiscriminator)
     return false;
+  if (!MF.getFunction().isDebugInfoForProfiling())
+    return false;
 
   bool Changed = false;
   using LocationDiscriminator = std::tuple<StringRef, unsigned, unsigned>;
   using BBSet = DenseSet<const MachineBasicBlock *>;
   using LocationDiscriminatorBBMap = DenseMap<LocationDiscriminator, BBSet>;
   using LocationDiscriminatorCurrPassMap =
       DenseMap<LocationDiscriminator, unsigned>;
 

llvm/test/CodeGen/X86/fsafdo_test1.ll

 ; RUN: llc -enable-fs-discriminator < %s | FileCheck %s
 ;
 ; Check that fs-afdo discriminators are generated.
 ; CHECK: .loc    1 7 3 is_stmt 0 discriminator 2 # foo.c:7:3
-; Check: .loc    1 9 5 is_stmt 1 discriminator 2 # foo.c:9:5
+; ChECK: .loc    1 9 5 is_stmt 1 discriminator 2 # foo.c:9:5
 ; CHECK: .loc    1 9 5 is_stmt 0 discriminator 11266 # foo.c:9:5
 ; CHECK: .loc    1 7 3 is_stmt 1 discriminator 11266 # foo.c:7:3
 ; Check that variable __llvm_fs_discriminator__ is generated.
 ; CHECK: .type   __llvm_fs_discriminator__,@object # @__llvm_fs_discriminator__
 ; CHECK: .section        .rodata,"a",@progbits
 ; CHECK: .weak   __llvm_fs_discriminator__
 ; CHECK: __llvm_fs_discriminator__:
 ; CHECK: .byte   1

 
 while.end4:
   ret i32 0, !dbg !12
 }
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!3, !4}
 
-!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, isOptimized: true, emissionKind: LineTablesOnly)
+!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: 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)

llvm/test/CodeGen/X86/fsafdo_test4.ll

 ; RUN: llc -enable-fs-discriminator < %s | FileCheck %s
 ;
-; Check that fs-afdo discriminators are generated.
+; Check that fs-afdo discriminators are NOT generated, as debugInfoForProfiling is false (not set).
 ; CHECK: .loc    1 7 3 is_stmt 0 discriminator 2 # foo.c:7:3
-; Check: .loc    1 9 5 is_stmt 1 discriminator 2 # foo.c:9:5
-; CHECK: .loc    1 9 5 is_stmt 0 discriminator 11266 # foo.c:9:5
-; CHECK: .loc    1 7 3 is_stmt 1 discriminator 11266 # foo.c:7:3
-; Check that variable __llvm_fs_discriminator__ is generated.
-; CHECK: .type   __llvm_fs_discriminator__,@object # @__llvm_fs_discriminator__
-; CHECK: .section        .rodata,"a",@progbits
-; CHECK: .weak   __llvm_fs_discriminator__
-; CHECK: __llvm_fs_discriminator__:
-; CHECK: .byte   1
-; CHECK: .size   __llvm_fs_discriminator__, 1
+; CHECK: .loc    1 9 5 is_stmt 1 discriminator 2 # foo.c:9:5
+; CHECK-NOT: .loc    1 9 5 is_stmt 0 discriminator 11266 # foo.c:9:5
+; CHECK-NOT: .loc    1 7 3 is_stmt 1 discriminator 11266 # foo.c:7:3
+; Check that variable __llvm_fs_discriminator__ is NOT generated.
+; CHECK-NOT: __llvm_fs_discriminator__:
 
 target triple = "x86_64-unknown-linux-gnu"
 
 %struct.Node = type { %struct.Node* }
 
 define i32 @foo(%struct.Node* readonly %node, %struct.Node* readnone %root) !dbg !6 {
 entry:
   %cmp = icmp eq %struct.Node* %node, %root, !dbg !8