[PseudoProbe] Do not force the calliste debug loc to inlined probes from __nodebug__ functions.

[hoy]

Summary

For pseudo probes we would like to keep their original dwarf discriminator (either a zero or null) until the first FS-discriminator pass. The inliner is a violation of that, given that it assigns inlinee instructions with no debug info with the that of the callsite. This is being disabled in this patch.

[wenlei]

For pseudo probes we would like to keep their original debug location

Is this accurate? we just don't want to have non-zero discriminator for probes, but we don't really care about whether their debug metadata point to original debug location or not. In this particular case, there's just no need to fill in call debug info if probe from inlinee originally doesn't have debug info.

llvm/lib/Transforms/Utils/InlineFunction.cpp

1645–1646

nit: follow the style above, as we don't want to make a single complicated condition check in the future.

// ...
if (isa<PseudoProbeInst>(BI))
  continue;

[hoy]

In D151568#4376679, @wenlei wrote:

For pseudo probes we would like to keep their original debug location

Is this accurate? we just don't want to have non-zero discriminator for probes, but we don't really care about whether their debug metadata point to original debug location or not. In this particular case, there's just no need to fill in call debug info if probe from inlinee originally doesn't have debug info.

Yeah, would be more accurate to say "keep their original dwarf discriminator".

[hoy]

Addressing comments.

[wenlei]

lgtm, thanks.

llvm/lib/Transforms/Utils/InlineFunction.cpp

for (BasicBlock::iterator BI = FI->begin(), BE = FI->end();
       // functions which must use caller location for all instructions in their
       // function body.
 
       // Don't update static allocas, as they may get moved later.
       if (auto *AI = dyn_cast<AllocaInst>(BI))
         if (allocaWouldBeStaticInEntry(AI))
           continue;
 
+      // Do not force a debug loc for pseudo probes, since they do not need to
+      // be debuggable, and also they are expected to have a zero/null dwarf
+      // discriminator at this point which could be violated otherwise.
+      if (isa<PseudoProbeInst>(BI))
+        continue;
+
       BI->setDebugLoc(TheCallDL);
     }
 
     // Remove debug info intrinsics if we're not keeping inline info.
     if (NoInlineLineTables) {
       BasicBlock::iterator BI = FI->begin();
       while (BI != FI->end()) {
         if (isa<DbgInfoIntrinsic>(BI)) {
           BI = BI->eraseFromParent();
           continue;

llvm/test/Transforms/SampleProfile/pseudo-probe-no-debug-info.ll

+; RUN: opt < %s -passes='pseudo-probe,cgscc(inline)' -S | FileCheck %s
+
+
+; CHECK-LABEL: @caller(
+
+; This instruction did not have a !dbg metadata in the callee but get a !dbg after inlined.
+; CHECK: store i32 1, {{.*}}, !dbg ![[#]]
+
+; This pseudo probe came from callee without a !dbg metadata.
+; CHECK-NOT:  call void @llvm.pseudoprobe({{.*}}), !dbg ![[#]]
+; CHECK:  call void @llvm.pseudoprobe({{.*}})
+
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@a = common global i32 0, align 4
+@b = common global i32 0, align 4
+
+; Function Attrs: nounwind uwtable
+define void @callee() #0 {
+entry:
+  store i32 1, ptr @a, align 4
+  ret void
+}
+
+; Function Attrs: nounwind uwtable
+define void @caller() #0 !dbg !4 {
+entry:
+  tail call void @callee(), !dbg !12
+  ret void, !dbg !12
+}
+
+attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "frame-pointer"="none" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!8, !9}
+!llvm.ident = !{!10}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, producer: "clang version 3.5.0 (210174)", isOptimized: true, emissionKind: LineTablesOnly, file: !1, enums: !2, retainedTypes: !2, globals: !2, imports: !2)
+!1 = !DIFile(filename: "test.c", directory: "/code/llvm/build0")
+!2 = !{}
+!4 = distinct !DISubprogram(name: "caller", line: 4, isLocal: false, isDefinition: true, virtualIndex: 6, isOptimized: true, unit: !0, scopeLine: 4, file: !1, scope: !5, type: !6, retainedNodes: !2)
+!5 = !DIFile(filename: "test.c", directory: "/code/llvm/build0")
+!6 = !DISubroutineType(types: !2)
+!7 = distinct !DISubprogram(name: "callee2", line: 2, isLocal: true, isDefinition: true, virtualIndex: 6, isOptimized: true, unit: !0, scopeLine: 2, file: !1, scope: !5, type: !6, retainedNodes: !2)
+!8 = !{i32 2, !"Dwarf Version", i32 4}
+!9 = !{i32 2, !"Debug Info Version", i32 3}
+!10 = !{!"clang version 3.5.0 (210174)"}
+!11 = !DILocation(line: 2, scope: !7)
+!12 = !DILocation(line: 4, scope: !4)