120 lines
3.4 KiB
LLVM
120 lines
3.4 KiB
LLVM
; RUN: opt -S -jump-threading < %s | FileCheck %s
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; Check that based solely on static profile estimation we don't update the
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; branch-weight metadata. Even if the function has an entry frequency, a
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; completely cold part of the CFG may be statically estimated.
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; For example in the loop below, jump threading would update the weight of the
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; loop-exiting branch to 0, drastically inflating the frequency of the loop
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; (in the range of billions).
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;
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; This is the CFG of the loop. There is no run-time profile info for edges
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; inside the loop, so branch and block frequencies are estimated as shown:
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;
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; check_1 (16)
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; (8) / |
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; eq_1 | (8)
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; \ |
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; check_2 (16)
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; (8) / |
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; eq_2 | (8)
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; \ |
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; check_3 (16)
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; (1) / |
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; (loop exit) | (15)
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; |
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; (back edge)
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;
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; First we thread eq_1->check_2 to check_3. Frequencies are updated to remove
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; the frequency of eq_1 from check_2 and then the false edge leaving check_2
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; (changed frequencies are highlighted with * *):
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;
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; check_1 (16)
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; (8) / |
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; eq_1~ | (8)
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; / |
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; / check_2 (*8*)
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; / (8) / |
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; \ eq_2 | (*0*)
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; \ \ |
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; ` --- check_3 (16)
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; (1) / |
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; (loop exit) | (15)
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; |
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; (back edge)
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;
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; Next we thread eq_1->check_3 and eq_2->check_3 to check_1 as new back edges.
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; Frequencies are updated to remove the frequency of eq_1 and eq_3 from
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; check_3 and then the false edge leaving check_3 (changed frequencies are
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; highlighted with * *):
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;
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; check_1 (16)
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; (8) / |
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; eq_1~ | (8)
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; / |
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; / check_2 (*8*)
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; / (8) / |
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; /-- eq_2~ | (*0*)
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; (back edge) |
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; check_3 (*0*)
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; (*0*) / |
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; (loop exit) | (*0*)
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; |
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; (back edge)
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;
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; As a result, the loop exit edge ends up with 0 frequency which in turn makes
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; the loop header to have maximum frequency.
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declare void @bar()
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define void @foo(i32 *%p, i32 %n) !prof !0 {
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entry:
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%enter_loop = icmp eq i32 %n, 0
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br i1 %enter_loop, label %exit, label %check_1, !prof !1
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; CHECK: br i1 %enter_loop, label %exit, label %check_1, !prof !1
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check_1:
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%v = load i32, i32* %p
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%cond1 = icmp eq i32 %v, 1
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br i1 %cond1, label %eq_1, label %check_2
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; No metadata:
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; CHECK: br i1 %cond1, label %check_2.thread, label %check_2{{$}}
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eq_1:
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call void @bar()
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br label %check_2
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; Verify the new backedge:
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; CHECK: check_2.thread:
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; CHECK-NEXT: call void @bar()
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; CHECK-NEXT: br label %check_1
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check_2:
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%cond2 = icmp eq i32 %v, 2
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br i1 %cond2, label %eq_2, label %check_3
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; No metadata:
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; CHECK: br i1 %cond2, label %eq_2, label %check_3{{$}}
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eq_2:
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call void @bar()
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br label %check_3
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; Verify the new backedge:
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; CHECK: eq_2:
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; CHECK-NEXT: call void @bar()
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; CHECK-NEXT: br label %check_1
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check_3:
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%condE = icmp eq i32 %v, 3
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br i1 %condE, label %exit, label %check_1
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; No metadata:
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; CHECK: br i1 %condE, label %exit, label %check_1{{$}}
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exit:
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ret void
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}
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!0 = !{!"function_entry_count", i64 120}
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; CHECK-NOT: branch_weights
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!1 = !{!"branch_weights", i32 119, i32 1}
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; CHECK: !1 = !{!"branch_weights", i32 119, i32 1}
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; CHECK-NOT: branch_weights
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