[CSSPGO] Tweakes to lower pseudo probe runtime overhead

[hoy]

Summary

A couple tweaks to

1. allow more thinlto importing by excluding probe intrinsics from IR size in module summary

2. Allow general default attributes (nofree nosync nounwind) for pseudo probe intrinsic. Without those attributes, pseudo probes will be basically treated as unknown calls which will in turn block their containing functions from annotated with those attributes.

[wenlei]

ltgm, thanks for the fix.

Allow general default attributes (nofree nosync nounwind) for pseudo probe intrinsic.

Can you expand in this commit message to also explain what problem this caused and fixed -- containing function cannot have these attribute.

llvm/lib/Analysis/ModuleSummaryAnalysis.cpp

282

Perhaps we should audit the use of DbgInfoIntrinsic to see if there're others that should be changed

[hoy]

In D109976#3006549, @wenlei wrote:

ltgm, thanks for the fix.

Allow general default attributes (nofree nosync nounwind) for pseudo probe intrinsic.

Can you expand in this commit message to also explain what problem this caused and fixed -- containing function cannot have these attribute.

Summary updated.

llvm/lib/Analysis/ModuleSummaryAnalysis.cpp

282

Good point. Will do.

llvm/include/llvm/IR/Intrinsics.td

 // that they are not removed even if they turn out to be empty, for languages
 // which specify that infinite loops must be preserved.
 def int_sideeffect : DefaultAttrsIntrinsic<[], [], [IntrInaccessibleMemOnly, IntrWillReturn]>;
 
 // The pseudoprobe intrinsic works as a place holder to the block it probes.
 // Like the sideeffect intrinsic defined above, this intrinsic is treated by the
 // optimizer as having opaque side effects so that it won't be get rid of or moved
 // out of the block it probes.
-def int_pseudoprobe : Intrinsic<[], [llvm_i64_ty, llvm_i64_ty, llvm_i32_ty, llvm_i64_ty],
+def int_pseudoprobe : DefaultAttrsIntrinsic<[], [llvm_i64_ty, llvm_i64_ty, llvm_i32_ty, llvm_i64_ty],
                                     [IntrInaccessibleMemOnly, IntrWillReturn]>;
 
 // Arithmetic fence intrinsic.
 def int_arithmetic_fence : Intrinsic<[llvm_anyfloat_ty], [LLVMMatchType<0>], [IntrNoMem]>;
 
 // Intrinsics to support half precision floating point format
 let IntrProperties = [IntrNoMem, IntrWillReturn] in {
 def int_convert_to_fp16   : DefaultAttrsIntrinsic<[llvm_i16_ty], [llvm_anyfloat_ty]>;

llvm/lib/Analysis/ModuleSummaryAnalysis.cpp

if (BB.hasAddressTaken()) {
       for (User *U : BlockAddress::get(const_cast<BasicBlock *>(&BB))->users())
         if (!isa<CallBrInst>(*U)) {
           HasIndirBranchToBlockAddress = true;
           break;
         }
     }
 
     for (const Instruction &I : BB) {
-      if (isa<DbgInfoIntrinsic>(I))
+      if (I.isDebugOrPseudoInst())
         continue;
       ++NumInsts;
       // Regular LTO module doesn't participate in ThinLTO import,
       // so no reference from it can be read/writeonly, since this
       // would require importing variable as local copy
       if (IsThinLTO) {
         if (isNonVolatileLoad(&I)) {
           // Postpone processing of non-volatile load instructions

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

 ; Check pseudo_probe metadata attached to the direct call instruction.
 ; CHECK-IL: call void @bar(i32 1), !dbg ![[#PROBE1:]]
 ; CHECK-MIR: PSEUDO_PROBE [[#GUID2]], 3, 2, 0
 ; CHECK-ASM: .pseudoprobe [[#GUID2]] 3 2 0
   call void @bar(i32 1)
   ret void
 }
 
+; CHECK-IL: Function Attrs: inaccessiblememonly nofree nosync nounwind willreturn
+; CHECK-IL-NEXT: declare void @llvm.pseudoprobe(i64, i64, i32, i64)
+
 ; CHECK-IL: ![[#FOO:]] = distinct !DISubprogram(name: "foo"
 ; CHECK-IL: ![[#FAKELINE]] = !DILocation(line: 0, scope: ![[#FOO]])
 ; CHECK-IL: ![[#REALLINE]] = !DILocation(line: 2, scope: ![[#FOO]])
 ; 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
 ;; with an index of 2.
 ; CHECK-IL: ![[#SCOPE0]] = !DILexicalBlockFile(scope: ![[#]], file: ![[#]], discriminator: 119537687)
 ; CHECK-IL: ![[#PROBE1]] = !DILocation(line: 0, scope: ![[#SCOPE1:]])