[SampleFDO] Fix invalid branch profile generated by indirect call promotion.

Suppose an inline instance has hot total sample count but 0 entry count, and
it is an indirect call target. If the indirect call has no other call target
and inline instance associated with it and it is promoted, currently the
conditional branch generated by indirect call promotion will have invalid
branch profile which is !{!"branch_weights", i32 0, i32 0} -- because the
entry count of the promoted target is 0 and the total entry count of all
targets is also 0. This caused a SEGV in Control Height Reduction and may
cause problem in other passes.

Function entry count of an inline instance is computed by a heuristic --
using either the sample of the starting line or starting inner inline
instance. The patch changes the heuristic a little bit so that when total
sample count is larger than 0, the computed entry count will be at least 1.
Then the new branch profile will be !{!"branch_weights", i32 1, i32 0}.

Differential Revision: https://reviews.llvm.org/D72790

llvm/include/llvm/ProfileData/SampleProf.h

@@ -416,21 +416,21 @@ public:
   /// Return the sample count of the first instruction of the function.
   /// The function can be either a standalone symbol or an inlined function.
   uint64_t getEntrySamples() const {
+    uint64_t Count = 0;
     // Use either BodySamples or CallsiteSamples which ever has the smaller
     // lineno.
     if (!BodySamples.empty() &&
         (CallsiteSamples.empty() ||
          BodySamples.begin()->first < CallsiteSamples.begin()->first))
-      return BodySamples.begin()->second.getSamples();
-    if (!CallsiteSamples.empty()) {
-      uint64_t T = 0;
+      Count = BodySamples.begin()->second.getSamples();
+    else if (!CallsiteSamples.empty()) {
       // An indirect callsite may be promoted to several inlined direct calls.
       // We need to get the sum of them.
       for (const auto &N_FS : CallsiteSamples.begin()->second)
-        T += N_FS.second.getEntrySamples();
-      return T;
+        Count += N_FS.second.getEntrySamples();
     }
-    return 0;
+    // Return at least 1 if total sample is not 0.
+    return Count ? Count : TotalSamples > 0;
   }
 
   /// Return all the samples collected in the body of the function.

llvm/test/Transforms/SampleProfile/Inputs/indirect-call.prof

@@ -29,3 +29,8 @@ return_arg_caller:3000:0
   11: 3000
  2: return_arg:3000
   1: 3000
+branch_prof_valid:4000:0
+ 1: 1000
+ 2: foo_inline3:3000
+  1: 0
+  2: 3000

llvm/test/Transforms/SampleProfile/indirect-call.ll

@@ -121,6 +121,19 @@ else:
   ret i32* null
 }
 
+; CHECK-LABEL: @branch_prof_valid
+; Check the conditional branch generated by indirect call promotion won't
+; have invalid profile like !{!"branch_weights", i32 0, i32 0}.
+define void @branch_prof_valid(void ()* %t0) !dbg !33 {
+  %t1 = alloca void ()*
+  store void ()* %t0, void ()** %t1
+  %t2 = load void ()*, void ()** %t1
+  ; CHECK-NOT: call {{.*}}
+  ; CHECK: br i1 {{.*}}, label %if.true.direct_targ, label %if.false.orig_indirect, {{.*}}, !prof ![[BR3:[0-9]+]]
+  call void %t2(), !dbg !34
+  ret void
+}
+
 @x = global i32 0, align 4
 @y = global void ()* null, align 8
 
@@ -148,6 +161,10 @@ define i32* @foo_inline2(i32* %x) !dbg !19 {
   ret i32* %x
 }
 
+define void @foo_inline3() !dbg !35 {
+  ret void
+}
+
 define i32 @foo_noinline(i32 %x) !dbg !20 {
   ret i32 %x
 }
@@ -184,6 +201,7 @@ define void @test_direct() !dbg !22 {
 ; CHECK: ![[BR1]] = !{!"branch_weights", i32 4000, i32 4000}
 ; CHECK: ![[BR2]] = !{!"branch_weights", i32 3000, i32 1000}
 ; CHECK: ![[VP]] = !{!"VP", i32 0, i64 8000, i64 -6391416044382067764, i64 1000}
+; CHECK: ![[BR3]] = !{!"branch_weights", i32 1, i32 0}
 !6 = distinct !DISubprogram(name: "test_inline", scope: !1, file: !1, line: 6, unit: !0)
 !7 = !DILocation(line: 7, scope: !6)
 !8 = distinct !DISubprogram(name: "test_inline_strip", scope: !1, file: !1, line: 8, unit: !0)
@@ -211,3 +229,6 @@ define void @test_direct() !dbg !22 {
 !30 = distinct !DISubprogram(name: "return_arg_caller", scope: !1, file: !1, line: 11, unit: !0)
 !31 = !DILocation(line: 12, scope: !30)
 !32 = !DILocation(line: 13, scope: !30)
+!33 = distinct !DISubprogram(name: "branch_prof_valid", scope: !1, file: !1, line: 25, unit: !0)
+!34 = !DILocation(line: 27, scope: !33)
+!35 = distinct !DISubprogram(name: "foo_inline3", scope: !1, file: !1, line: 29, unit: !0)

llvm/test/Transforms/SampleProfile/inline-callee-update.ll

@@ -5,6 +5,7 @@
 @y = global i32* ()* null, align 8
 @z = global i32* ()* null, align 8
 
+; CHECK: define i32* @sample_loader_inlinee() {{.*}} !prof ![[ENTRY:[0-9]+]]
 define i32* @sample_loader_inlinee() !dbg !3 {
 bb:
   %tmp = call i32* @direct_leaf_func(i32* null), !dbg !4
@@ -20,6 +21,7 @@ else:                                             ; preds = %bb
   ret i32* null
 }
 
+; CHECK: define i32* @cgscc_inlinee() {{.*}} !prof ![[ENTRY:[0-9]+]]
 define i32* @cgscc_inlinee() !dbg !6 {
 bb:
   %tmp = call i32* @direct_leaf_func(i32* null), !dbg !7
@@ -67,7 +69,4 @@ declare i32* @direct_leaf_func(i32*)
 !12 = !DILocation(line: 21, scope: !11)
 
 ; Make sure the ImportGUID stays with entry count metadata for ThinLTO-PreLink
-; CHECK: distinct !DISubprogram(name: "sample_loader_inlinee"
-; CHECK-NEXT: {!"function_entry_count", i64 1, i64 -9171813444624716006}
-; CHECK: distinct !DISubprogram(name: "cgscc_inlinee"
-; CHECK-NEXT: !{!"function_entry_count", i64 0, i64 -9171813444624716006}
+; CHECK: ![[ENTRY]] = !{!"function_entry_count", i64 1, i64 -9171813444624716006}