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1; RUN: opt -S -passes=jump-threading < %s | FileCheck %s2 3; Check that based solely on static profile estimation we don't update the4; branch-weight metadata. Even if the function has an entry frequency, a5; completely cold part of the CFG may be statically estimated.6 7; For example in the loop below, jump threading would update the weight of the8; loop-exiting branch to 0, drastically inflating the frequency of the loop9; (in the range of billions).10;11; This is the CFG of the loop. There is no run-time profile info for edges12; inside the loop, so branch and block frequencies are estimated as shown:13;14; check_1 (16)15; (8) / |16; eq_1 | (8)17; \ |18; check_2 (16)19; (8) / |20; eq_2 | (8)21; \ |22; check_3 (16)23; (1) / |24; (loop exit) | (15)25; |26; latch27; |28; (back edge)29;30; First we thread eq_1->check_2 to check_3. Frequencies are updated to remove31; the frequency of eq_1 from check_2 and then the false edge leaving check_232; (changed frequencies are highlighted with * *):33;34; check_1 (16)35; (8) / |36; eq_1~ | (8)37; / |38; / check_2 (*8*)39; / (8) / |40; \ eq_2 | (*0*)41; \ \ |42; ` --- check_3 (16)43; (1) / |44; (loop exit) | (15)45; |46; latch47; |48; (back edge)49;50; Next we thread eq_1->check_3 and eq_2->check_3 to check_1 as new edges to51; the loop latch. Frequencies are updated to remove the frequency of eq_152; and eq_3 from check_3 and then the false edge leaving check_3 (changed53; frequencies are highlighted with * *):54;55; check_1 (16)56; (8) / |57; eq_1~ | (8)58; / |59; / check_2 (*8*)60; / (8) / |61; /-- eq_2~ | (*0*)62; / |63; / check_3 (*0*)64; / (*0*) / |65; | (loop exit) | (*0*)66; \ |67; `--------- latch68; |69; (back edge)70;71; As a result, the loop exit edge ends up with 0 frequency which in turn makes72; the loop header to have maximum frequency.73 74declare void @bar()75 76define void @foo(ptr %p, i32 %n) !prof !0 {77entry:78 %enter_loop = icmp eq i32 %n, 079 br i1 %enter_loop, label %exit, label %check_1, !prof !180; CHECK: br i1 %enter_loop, label %exit, label %check_1, !prof !181 82check_1:83 %v = load i32, ptr %p84 %cond1 = icmp eq i32 %v, 185 br i1 %cond1, label %eq_1, label %check_286; No metadata:87; CHECK: br i1 %cond1, label %check_2.thread, label %check_2{{$}}88 89eq_1:90 call void @bar()91 br label %check_292; Verify the new edge:93; CHECK: check_2.thread:94; CHECK-NEXT: call void @bar()95; CHECK-NEXT: br label %latch96 97check_2:98 %cond2 = icmp eq i32 %v, 299 br i1 %cond2, label %eq_2, label %check_3100; No metadata:101; CHECK: br i1 %cond2, label %eq_2, label %check_3{{$}}102 103eq_2:104 call void @bar()105 br label %check_3106; Verify the new edge:107; CHECK: eq_2:108; CHECK-NEXT: call void @bar()109; CHECK-NEXT: br label %latch110 111check_3:112 %condE = icmp eq i32 %v, 3113 br i1 %condE, label %exit, label %latch114; No metadata:115; CHECK: br i1 %condE, label %exit, label %latch{{$}}116 117latch:118 br label %check_1119 120exit:121 ret void122}123 124!0 = !{!"function_entry_count", i64 120}125; CHECK-NOT: branch_weights126!1 = !{!"branch_weights", i32 119, i32 1}127; CHECK: !1 = !{!"branch_weights", i32 119, i32 1}128; CHECK-NOT: branch_weights129