[GCOVProfiling] don't profile Fn's w/ noprofile attribute

[nickdesaulniers]

Summary

Similar to D104475, the Linux kernel would like to avoid compiler
generated code in certain functions. The no_profile function
attribute can be used in C to generate the the noprofile fn attr in IR.
Respect that from GCOVProfiling.

Link: https://lore.kernel.org/lkml/[e-mail]/

[nickdesaulniers]

TODO(Nick): trim down test case further.

[MaskRay]

llvm/test/Transforms/GCOVProfiling/noprofile.ll

2

You may use module-flags.ll as a template. It is simple enough.

[nickdesaulniers]

• reduce test case, remove WIP

[nickdesaulniers]

• refresh utils/update_test_checks.py assertions

[MaskRay]

llvm/test/Transforms/GCOVProfiling/noprofile.ll

3

< %s

Add a file-level comment: Test that the noprofile attribute disables profiling.

4

s/#0/noprofile

in-line attributes are usually clearer for testing purpose.

[MaskRay]

Signed-off-by: Nick Desaulniers <[e-mail]>

We don't use the tag.

[nickdesaulniers]

• test mods: add comment, remove -o -, in-line noprofile attr

llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp

for (unsigned i = 0, e = CUNode->getNumOperands(); i != e; ++i) {
     for (auto &F : M->functions()) {
       DISubprogram *SP = F.getSubprogram();
       unsigned EndLine;
       if (!SP) continue;
       if (!functionHasLines(F, EndLine) || !isFunctionInstrumented(F))
         continue;
       // TODO: Functions using scope-based EH are currently not supported.
       if (isUsingScopeBasedEH(F)) continue;
+      if (F.hasFnAttribute(llvm::Attribute::NoProfile))
+        continue;
 
       // Add the function line number to the lines of the entry block
       // to have a counter for the function definition.
       uint32_t Line = SP->getLine();
       auto Filename = getFilename(SP);
 
       BranchProbabilityInfo *BPI = GetBPI(F);
       BlockFrequencyInfo *BFI = GetBFI(F);

llvm/test/Transforms/GCOVProfiling/noprofile.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=insert-gcov-profiling -S %s | FileCheck %s
+
+; Test that the noprofile attribute disables profiling.
+define dso_local i32 @no_instr(i32 %a) noprofile !dbg !9 {
+; CHECK-LABEL: @no_instr(
+; CHECK-NEXT:    ret i32 42, !dbg [[DBG6:![0-9]+]]
+;
+  ret i32 42, !dbg !27
+}
+
+define dso_local i32 @instr(i32 %a) !dbg !28 {
+; CHECK-LABEL: @instr(
+; CHECK-NEXT:    [[GCOV_CTR:%.*]] = load i64, i64* getelementptr inbounds ([1 x i64], [1 x i64]* @__llvm_gcov_ctr, i64 0, i64 0), align 4, !dbg [[DBG8:![0-9]+]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[GCOV_CTR]], 1, !dbg [[DBG8]]
+; CHECK-NEXT:    store i64 [[TMP1]], i64* getelementptr inbounds ([1 x i64], [1 x i64]* @__llvm_gcov_ctr, i64 0, i64 0), align 4, !dbg [[DBG8]]
+; CHECK-NEXT:    ret i32 42, !dbg [[DBG8]]
+;
+  ret i32 42, !dbg !44
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "a.c", directory: "")
+!2 = !{}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = distinct !DISubprogram(name: "no_instr", scope: !1, file: !1, line: 5, type: !10, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!10 = !DISubroutineType(types: !2)
+!27 = !DILocation(line: 9, column: 3, scope: !9)
+!28 = distinct !DISubprogram(name: "instr", scope: !1, file: !1, line: 12, type: !10, scopeLine: 12, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!44 = !DILocation(line: 16, column: 3, scope: !28)