[llvm] [TRE] Adjust function entry count when using instrumented profiles (PR #143987)

[Joel E. Denny via llvm-commits]

================
@@ -0,0 +1,167 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals
+; RUN: opt -passes=tailcallelim -S %s -o - | FileCheck %s
+; RUN: opt -passes=tailcallelim -tre-disable-entrycount-recompute -S %s -o - | FileCheck %s --check-prefix=DISABLED
+
+; Test that tail call elimination correctly adjusts function entry counts
+; when eliminating tail recursive calls.
+
+; Basic test: eliminate a tail call and adjust entry count
+define i32 @test_basic_entry_count_adjustment(i32 %n) !prof !0 {
+; CHECK-LABEL: @test_basic_entry_count_adjustment(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[TAILRECURSE:%.*]]
+; CHECK:       tailrecurse:
+; CHECK-NEXT:    [[N_TR:%.*]] = phi i32 [ [[N:%.*]], [[ENTRY:%.*]] ], [ [[SUB:%.*]], [[IF_THEN:%.*]] ]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[N_TR]], 0
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN]], label [[IF_ELSE:%.*]], !prof [[PROF1:![0-9]+]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[SUB]] = sub i32 [[N_TR]], 1
+; CHECK-NEXT:    br label [[TAILRECURSE]]
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i32 0
+;
+; DISABLED-LABEL: @test_basic_entry_count_adjustment(
+; DISABLED-NEXT:  entry:
+; DISABLED-NEXT:    br label [[TAILRECURSE:%.*]]
+; DISABLED:       tailrecurse:
+; DISABLED-NEXT:    [[N_TR:%.*]] = phi i32 [ [[N:%.*]], [[ENTRY:%.*]] ], [ [[SUB:%.*]], [[IF_THEN:%.*]] ]
+; DISABLED-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[N_TR]], 0
+; DISABLED-NEXT:    br i1 [[CMP]], label [[IF_THEN]], label [[IF_ELSE:%.*]], !prof [[PROF1:![0-9]+]]
+; DISABLED:       if.then:
+; DISABLED-NEXT:    [[SUB]] = sub i32 [[N_TR]], 1
+; DISABLED-NEXT:    br label [[TAILRECURSE]]
+; DISABLED:       if.else:
+; DISABLED-NEXT:    ret i32 0
+;
+entry:
+  %cmp = icmp sgt i32 %n, 0
+  br i1 %cmp, label %if.then, label %if.else, !prof !1
+
+if.then:                                          ; preds = %entry
+  %sub = sub i32 %n, 1
+  %call = tail call i32 @test_basic_entry_count_adjustment(i32 %sub)
+  ret i32 %call
+
+if.else:                                          ; preds = %entry
+  ret i32 0
+}
+
+; Test multiple tail calls in different blocks with different frequencies
+define i32 @test_multiple_blocks_entry_count(i32 %n, i32 %flag) !prof !2 {
+; CHECK-LABEL: @test_multiple_blocks_entry_count(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[TAILRECURSE:%.*]]
+; CHECK:       tailrecurse:
+; CHECK-NEXT:    [[N_TR:%.*]] = phi i32 [ [[N:%.*]], [[ENTRY:%.*]] ], [ [[SUB1:%.*]], [[BLOCK1:%.*]] ], [ [[SUB2:%.*]], [[BLOCK2:%.*]] ]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[N_TR]], 0
+; CHECK-NEXT:    br i1 [[CMP]], label [[CHECK_FLAG:%.*]], label [[BASE_CASE:%.*]]
+; CHECK:       check.flag:
+; CHECK-NEXT:    [[CMP_FLAG:%.*]] = icmp eq i32 [[FLAG:%.*]], 1
+; CHECK-NEXT:    br i1 [[CMP_FLAG]], label [[BLOCK1]], label [[BLOCK2]], !prof [[PROF3:![0-9]+]]
+; CHECK:       block1:
+; CHECK-NEXT:    [[SUB1]] = sub i32 [[N_TR]], 1
+; CHECK-NEXT:    br label [[TAILRECURSE]]
+; CHECK:       block2:
+; CHECK-NEXT:    [[SUB2]] = sub i32 [[N_TR]], 2
+; CHECK-NEXT:    br label [[TAILRECURSE]]
+; CHECK:       base.case:
+; CHECK-NEXT:    ret i32 1
+;
+; DISABLED-LABEL: @test_multiple_blocks_entry_count(
+; DISABLED-NEXT:  entry:
+; DISABLED-NEXT:    br label [[TAILRECURSE:%.*]]
+; DISABLED:       tailrecurse:
+; DISABLED-NEXT:    [[N_TR:%.*]] = phi i32 [ [[N:%.*]], [[ENTRY:%.*]] ], [ [[SUB1:%.*]], [[BLOCK1:%.*]] ], [ [[SUB2:%.*]], [[BLOCK2:%.*]] ]
+; DISABLED-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[N_TR]], 0
+; DISABLED-NEXT:    br i1 [[CMP]], label [[CHECK_FLAG:%.*]], label [[BASE_CASE:%.*]]
+; DISABLED:       check.flag:
+; DISABLED-NEXT:    [[CMP_FLAG:%.*]] = icmp eq i32 [[FLAG:%.*]], 1
+; DISABLED-NEXT:    br i1 [[CMP_FLAG]], label [[BLOCK1]], label [[BLOCK2]], !prof [[PROF3:![0-9]+]]
+; DISABLED:       block1:
+; DISABLED-NEXT:    [[SUB1]] = sub i32 [[N_TR]], 1
+; DISABLED-NEXT:    br label [[TAILRECURSE]]
+; DISABLED:       block2:
+; DISABLED-NEXT:    [[SUB2]] = sub i32 [[N_TR]], 2
+; DISABLED-NEXT:    br label [[TAILRECURSE]]
+; DISABLED:       base.case:
+; DISABLED-NEXT:    ret i32 1
+;
+entry:
+  %cmp = icmp sgt i32 %n, 0
+  br i1 %cmp, label %check.flag, label %base.case
----------------
jdenny-ornl wrote:

Is the lack of a !prof on this branch intentional?  What does it assume for the branch weights?  How is the new function entry count of 859 computed?

https://github.com/llvm/llvm-project/pull/143987