[PGO] Fix select instruction annotation

Summary:
Select instruction annotation in IR PGO uses the edge count to infer the
branch count. It's currently placed in setInstrumentedCounts() where
no all the BB counts have been computed. This leads to wrong branch weights.
Move the annotation after all BB counts are populated.

Reviewers: davidxl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D25961

llvm-svn: 285128

llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp

@@ -642,7 +642,7 @@ public:
              BranchProbabilityInfo *BPI = nullptr,
              BlockFrequencyInfo *BFI = nullptr)
       : F(Func), M(Modu), FuncInfo(Func, ComdatMembers, false, BPI, BFI),
-        FreqAttr(FFA_Normal) {}
+        CountPosition(0), ProfileCountSize(0), FreqAttr(FFA_Normal) {}
 
   // Read counts for the instrumented BB from profile.
   bool readCounters(IndexedInstrProfReader *PGOReader);
@@ -682,6 +682,12 @@ private:
   // compilation.
   uint64_t ProgramMaxCount;
 
+  // Position of counter that remains to be read.
+  uint32_t CountPosition;
+
+  // Total size of the profile count for this function.
+  uint32_t ProfileCountSize;
+
   // ProfileRecord for this function.
   InstrProfRecord ProfileRecord;
 
@@ -750,9 +756,8 @@ void PGOUseFunc::setInstrumentedCounts(
     NewEdge1.InMST = true;
     getBBInfo(InstrBB).setBBInfoCount(CountValue);
   }
-  // Now annotate select instructions
-  FuncInfo.SIVisitor.annotateSelects(F, this, &I);
-  assert(I == CountFromProfile.size());
+  ProfileCountSize =  CountFromProfile.size();
+  CountPosition = I;
 }
 
 // Set the count value for the unknown edge. There should be one and only one
@@ -892,6 +897,10 @@ void PGOUseFunc::populateCounters() {
     FuncMaxCount = std::max(FuncMaxCount, getBBInfo(&BB).CountValue);
   markFunctionAttributes(FuncEntryCount, FuncMaxCount);
 
+  // Now annotate select instructions
+  FuncInfo.SIVisitor.annotateSelects(F, this, &CountPosition);
+  assert(CountPosition == ProfileCountSize);
+
   DEBUG(FuncInfo.dumpInfo("after reading profile."));
 }
 

llvm/test/Transforms/PGOProfile/Inputs/select2.proftext

@@ -0,0 +1,11 @@
+# IR level Instrumentation Flag
+:ir
+foo
+# Func Hash:
+72057628175588252
+# Num Counters:
+3
+# Counter Values:
+800
+3
+300

llvm/test/Transforms/PGOProfile/select2.ll

@@ -0,0 +1,37 @@
+; RUN: llvm-profdata merge %S/Inputs/select2.proftext -o %t.profdata
+; RUN: opt < %s -pgo-instr-use -pgo-test-profile-file=%t.profdata -pgo-instr-select=true -S | FileCheck %s --check-prefix=USE
+; RUN: opt < %s -passes=pgo-instr-use -pgo-test-profile-file=%t.profdata -pgo-instr-select=true -S | FileCheck %s --check-prefix=USE
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @foo(i32 %n) {
+;USE: define i32 @foo(i32 %n) !prof ![[ENTRY_COUNT:[0-9]+]] {
+entry:
+  br label %for.cond
+
+for.cond:
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+  %sum.0 = phi i32 [ 0, %entry ], [ %add, %for.inc ]
+  %cmp = icmp slt i32 %i.0, %n
+  br i1 %cmp, label %for.body, label %for.end
+;USE:  br i1 %cmp, label %for.body, label %for.end, !prof ![[BW_FOR_BR:[0-9]+]]
+
+for.body:
+  %cmp1 = icmp sgt i32 %sum.0, 10
+  %cond = select i1 %cmp1, i32 20, i32 -10
+;USE:  %cond = select i1 %cmp1, i32 20, i32 -10, !prof ![[BW_FOR_SELECT:[0-9]+]]
+  %add = add nsw i32 %sum.0, %cond
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i32 %i.0, 1
+  br label %for.cond
+
+for.end:
+  ret i32 %sum.0
+}
+
+;USE: ![[ENTRY_COUNT]] = !{!"function_entry_count", i64 3}
+;USE: ![[BW_FOR_BR]] = !{!"branch_weights", i32 800, i32 3}
+;USE: ![[BW_FOR_SELECT]] = !{!"branch_weights", i32 300, i32 500}