[llvm] [SLU][profcheck] Estimate branch weights in partial unswitch cases (PR #164035)

[Mircea Trofin via llvm-commits]

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@@ -0,0 +1,157 @@
+; RUN: split-file %s %t
+; RUN: cat %t/main.ll %t/probable-or.prof > %t/probable-or.ll
+; RUN: cat %t/main.ll %t/probable-and.prof > %t/probable-and.ll
+; RUN: opt -passes='loop-mssa(simple-loop-unswitch)' -S %t/probable-or.ll -o - | FileCheck %t/probable-or.prof
+; RUN: opt -passes='loop-mssa(simple-loop-unswitch)' -S %t/probable-and.ll -o - | FileCheck %t/probable-and.prof
+;
+; RUN: opt -passes='module(print<block-freq>),function(loop-mssa(simple-loop-unswitch)),module(print<block-freq>)' \
+; RUN:   %t/probable-or.ll -disable-output -simple-loop-unswitch-estimate-profile=0 2>&1 | FileCheck %t/probable-or.prof --check-prefixes=PROFILE-COM,PROFILE-REF
+
+; RUN: opt -passes='module(print<block-freq>),function(loop-mssa(simple-loop-unswitch)),module(print<block-freq>)' \
+; RUN:   %t/probable-or.ll -disable-output -simple-loop-unswitch-estimate-profile=1 2>&1 | FileCheck %t/probable-or.prof --check-prefixes=PROFILE-COM,PROFILE-CHK
+
+; RUN: opt -passes='module(print<block-freq>),function(loop-mssa(simple-loop-unswitch)),module(print<block-freq>)' \
+; RUN:   %t/probable-and.ll -disable-output -simple-loop-unswitch-estimate-profile=0 2>&1 | FileCheck %t/probable-and.prof --check-prefixes=PROFILE-COM,PROFILE-REF
+
+; RUN: opt -passes='module(print<block-freq>),function(loop-mssa(simple-loop-unswitch)),module(print<block-freq>)' \
+; RUN:   %t/probable-and.ll -disable-output -simple-loop-unswitch-estimate-profile=1 2>&1 | FileCheck %t/probable-and.prof --check-prefixes=PROFILE-COM,PROFILE-CHK
+
+;--- main.ll
+declare void @some_func() noreturn
+
+define i32 @or(i1 %cond1, i32 %var1) !prof !0 {
+entry:
+  br label %loop_begin
+
+loop_begin:
+  %var3 = phi i32 [%var1, %entry], [%var2, %do_something]
+  %cond2 = icmp eq i32 %var3, 10
+  %cond.or = or i1 %cond1, %cond2
+  br i1 %cond.or, label %loop_exit, label %do_something, !prof !1
+
+do_something:
+  %var2 = add i32 %var3, 1
+  call void @some_func() noreturn nounwind
+  br label %loop_begin
+
+loop_exit:
+  ret i32 0
+}
+
+define i32 @and(i1 %cond1, i32 %var1) !prof !0 {
+entry:
+  br label %loop_begin
+
+loop_begin:
+  %var3 = phi i32 [%var1, %entry], [%var2, %do_something]
+  %cond2 = icmp eq i32 %var3, 10
+  %cond.and = and i1 %cond1, %cond2
+  br i1 %cond.and, label %do_something, label %loop_exit, !prof !1
+
+do_something:
+  %var2 = add i32 %var3, 1
+  call void @some_func() noreturn nounwind
+  br label %loop_begin
+
+loop_exit:
+  ret i32 0
+}
+
+;--- probable-or.prof
+!0 = !{!"function_entry_count", i32 10}
+!1 = !{!"branch_weights", i32 1, i32 1000}
+; CHECK-LABEL: @or
+; CHECK-LABEL: entry:
+; CHECK-NEXT:   %cond1.fr = freeze i1 %cond1
+; CHECK-NEXT:   br i1 %cond1.fr, label %loop_exit.split, label %entry.split, !prof !1
+; CHECK-LABEL: @and
+; CHECK-LABEL: entry:
+; CHECK-NEXT:   %cond1.fr = freeze i1 %cond1
+; CHECK-NEXT:   br i1 %cond1.fr, label %entry.split, label %loop_exit.split, !prof !2
+; CHECK: !1 = !{!"branch_weights", i32 1, i32 1000}
+; CHECK: !2 = !{!"unknown", !"simple-loop-unswitch"}
+
+; PROFILE-COM: Printing analysis results of BFI for function 'or':
+; PROFILE-COM: block-frequency-info: or
+ ; PROFILE-COM: - entry: {{.*}} count = 10
+ ; PROFILE-COM: - loop_begin: {{.*}} count = 10010
+ ; PROFILE-COM: - do_something: {{.*}} count = 10000
+ ; PROFILE-COM: - loop_exit: {{.*}} count = 10
+
+; PROFILE-COM: Printing analysis results of BFI for function 'and':
+; PROFILE-COM: block-frequency-info: and
+ ; PROFILE-COM: - entry: {{.*}} count = 10
+ ; PROFILE-COM: - loop_begin: {{.*}} count = 10
+ ; PROFILE-COM: - do_something: {{.*}} count = 0
+ ; PROFILE-COM: - loop_exit: {{.*}} count = 10
+
+; PROFILE-COM: Printing analysis results of BFI for function 'or':
+; PROFILE-COM: block-frequency-info: or
+ ; PROFILE-COM: - entry: {{.*}} count = 10
+ ; PROFILE-REF: - entry.split: {{.*}} count = 5
+ ; PROFILE-CHK: - entry.split: {{.*}} count = 10
+ ; PROFILE-REF: - loop_begin: {{.*}} count = 5005
+ ; PROFILE-CHK: - loop_begin: {{.*}} count = 10000
+ ; PROFILE-REF: - do_something: {{.*}} count = 5000
+ ; PROFILE-CHK: - do_something: {{.*}} count = 9990
----------------
mtrofin wrote:

Yes - which is why I was wondering in the PR-level comment if maybe I should use BFIs as the invariants from which to calculate the new `!prof`. I didn't think hard about it, and it *might* be more complex than this change, hence offered it as a point of discussion. If we think there's some merit to it, I would prefer adding an issue for looking more at it in phase 2 (when we look at `!prof` values); and land this change, as it is still an improvement.

https://github.com/llvm/llvm-project/pull/164035