InstrProf: Mark BiasLI as invariant. (#95588)

Bias doesn't change after startup.

The test is enhanced for optimized sequences and atomic ops.

Author: chapuni

llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp

@@ -945,6 +945,9 @@ Value *InstrLowerer::getCounterAddress(InstrProfCntrInstBase *I) {
     IRBuilder<> EntryBuilder(&Fn->getEntryBlock().front());
     auto *Bias = getOrCreateBiasVar(getInstrProfCounterBiasVarName());
     BiasLI = EntryBuilder.CreateLoad(Int64Ty, Bias, "profc_bias");
+    // Bias doesn't change after startup.
+    BiasLI->setMetadata(LLVMContext::MD_invariant_load,
+                        MDNode::get(M.getContext(), std::nullopt));
   }
   auto *Add = Builder.CreateAdd(Builder.CreatePtrToInt(Addr, Int64Ty), BiasLI);
   return Builder.CreateIntToPtr(Add, Addr->getType());

llvm/test/Instrumentation/InstrProfiling/runtime-counter-relocation.ll

@@ -1,9 +1,13 @@
 ; RUN: opt < %s -S -passes=instrprof | FileCheck %s
 ; RUN: opt < %s -S -passes=instrprof -runtime-counter-relocation | FileCheck -check-prefixes=RELOC %s
+; RUN: opt < %s -S -passes=instrprof,inline,gvn -runtime-counter-relocation | FileCheck -check-prefixes=RELOC,RELOCOPT %s
+; RUN: opt < %s -S -passes=instrprof            -runtime-counter-relocation -instrprof-atomic-counter-update-all | FileCheck -check-prefixes=ATOMIC %s
+; RUN: opt < %s -S -passes=instrprof,inline,gvn -runtime-counter-relocation -instrprof-atomic-counter-update-all | FileCheck -check-prefixes=ATOMIC,ATOMICOPT %s
 
 target triple = "x86_64-unknown-linux-gnu"
 
 @__profn_foo = private constant [3 x i8] c"foo"
+@__profn_bar = private constant [3 x i8] c"bar"
 ; RELOC: $__llvm_profile_counter_bias = comdat any
 ; RELOC: @__llvm_profile_counter_bias = linkonce_odr hidden global i64 0, comdat
 
@@ -12,14 +16,34 @@ target triple = "x86_64-unknown-linux-gnu"
 ; CHECK-NEXT: %[[PGOCOUNTINC:.+]] = add i64 %[[PGOCOUNT]], 1
 ; CHECK-NEXT: store i64 %[[PGOCOUNTINC]], ptr @__profc_foo
 ; RELOC-LABEL: define void @foo
-; RELOC-NEXT: %[[BIAS:.+]] = load i64, ptr @__llvm_profile_counter_bias
+; RELOC-NEXT: %[[BIAS:.+]] = load i64, ptr @__llvm_profile_counter_bias, align 8, !invariant.load !0
 ; RELOC-NEXT: %[[PROFC_BIAS:.+]] = add i64 ptrtoint (ptr @__profc_foo to i64), %[[BIAS]]
 ; RELOC-NEXT: %[[PROFC_ADDR:.+]] = inttoptr i64 %[[PROFC_BIAS]] to ptr
 ; RELOC-NEXT: %[[PGOCOUNT:.+]] = load i64, ptr %[[PROFC_ADDR]]
 ; RELOC-NEXT: %[[PGOCOUNTINC:.+]] = add i64 %[[PGOCOUNT]], 1
 ; RELOC-NEXT: store i64 %[[PGOCOUNTINC]], ptr %[[PROFC_ADDR]]
+; RELOCOPT-NEXT: %[[PROFC_BIAS1:.+]] = add i64 ptrtoint (ptr @__profc_bar to i64), %[[BIAS]]
+; RELOCOPT-NEXT: %[[PROFC_ADDR1:.+]] = inttoptr i64 %[[PROFC_BIAS1]] to ptr
+; RELOCOPT-NEXT: %[[PGOCOUNT1:.+]] = load i64, ptr %[[PROFC_ADDR1]]
+; RELOCOPT-NEXT: %[[PGOCOUNTINC1:.+]] = add i64 %[[PGOCOUNT1]], 1
+; RELOCOPT-NEXT: store i64 %[[PGOCOUNTINC1]], ptr %[[PROFC_ADDR1]]
+; ATOMIC-LABEL: define void @foo
+; ATOMIC-NEXT: %[[BIAS:.+]] = load i64, ptr @__llvm_profile_counter_bias, align 8, !invariant.load !0
+; ATOMIC-NEXT: %[[PROFC_BIAS:.+]] = add i64 ptrtoint (ptr @__profc_foo to i64), %[[BIAS]]
+; ATOMIC-NEXT: %[[PROFC_ADDR:.+]] = inttoptr i64 %[[PROFC_BIAS]] to ptr
+; ATOMIC-NEXT: %[[PGOCOUNTINC:.+]] = atomicrmw add ptr %[[PROFC_ADDR]], i64 1 monotonic
+; ATOMICOPT-NEXT: %[[PROFC_BIAS1:.+]] = add i64 ptrtoint (ptr @__profc_bar to i64), %[[BIAS]]
+; ATOMICOPT-NEXT: %[[PROFC_ADDR1:.+]] = inttoptr i64 %[[PROFC_BIAS1]] to ptr
+; ATOMICOPT-NEXT: %[[PGOCOUNTINC1:.+]] = atomicrmw add ptr %[[PROFC_ADDR1]], i64 1 monotonic
+
+define void @bar() {
+  call void @llvm.instrprof.increment(ptr @__profn_bar, i64 0, i32 1, i32 0)
+  ret void
+}
+
 define void @foo() {
   call void @llvm.instrprof.increment(ptr @__profn_foo, i64 0, i32 1, i32 0)
+  call void @bar()
   ret void
 }