1; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s 2 3target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" 4 5@A = weak global [1000 x i32] zeroinitializer, align 32 6 7; The resulting predicate is i16 {0,+,1} <nssw>, meanining 8; that the resulting backedge expression will be valid for: 9; (1 + (-1 smax %M)) <= MAX_INT16 10; 11; At the limit condition for M (MAX_INT16 - 1) we have in the 12; last iteration: 13; i0 <- MAX_INT16 14; i0.ext <- MAX_INT16 15; 16; and therefore no wrapping happend for i0 or i0.ext 17; throughout the execution of the loop. The resulting predicated 18; backedge taken count is correct. 19 20; CHECK: Classifying expressions for: @test1 21; CHECK: %i.0.ext = sext i16 %i.0 to i32 22; CHECK-NEXT: --> (sext i16 {0,+,1}<%bb3> to i32) 23; CHECK: Loop %bb3: Unpredictable backedge-taken count. 24; CHECK-NEXT: Loop %bb3: Unpredictable max backedge-taken count. 25; CHECK-NEXT: Loop %bb3: Predicated backedge-taken count is (1 + (-1 smax %M)) 26; CHECK-NEXT: Predicates: 27; CHECK-NEXT: {0,+,1}<%bb3> Added Flags: <nssw> 28define void @test1(i32 %N, i32 %M) { 29entry: 30 br label %bb3 31 32bb: ; preds = %bb3 33 %tmp = getelementptr [1000 x i32], [1000 x i32]* @A, i32 0, i16 %i.0 ; <i32*> [#uses=1] 34 store i32 123, i32* %tmp 35 %tmp2 = add i16 %i.0, 1 ; <i32> [#uses=1] 36 br label %bb3 37 38bb3: ; preds = %bb, %entry 39 %i.0 = phi i16 [ 0, %entry ], [ %tmp2, %bb ] ; <i32> [#uses=3] 40 %i.0.ext = sext i16 %i.0 to i32 41 %tmp3 = icmp sle i32 %i.0.ext, %M ; <i1> [#uses=1] 42 br i1 %tmp3, label %bb, label %bb5 43 44bb5: ; preds = %bb3 45 br label %return 46 47return: ; preds = %bb5 48 ret void 49} 50 51; The predicated backedge taken count is: 52; (2 + (zext i16 %Start to i32) + ((-2 + (-1 * (sext i16 %Start to i32))) 53; smax (-1 + (-1 * %M))) 54; ) 55 56; -1 + (-1 * %M) <= (-2 + (-1 * (sext i16 %Start to i32)) 57; The predicated backedge taken count is 0. 58; From the IR, this is correct since we will bail out at the 59; first iteration. 60 61 62; * -1 + (-1 * %M) > (-2 + (-1 * (sext i16 %Start to i32)) 63; or: %M < 1 + (sext i16 %Start to i32) 64; 65; The predicated backedge taken count is 1 + (zext i16 %Start to i32) - %M 66; 67; If %M >= MIN_INT + 1, this predicated backedge taken count would be correct (even 68; without predicates). However, for %M < MIN_INT this would be an infinite loop. 69; In these cases, the {%Start,+,-1} <nusw> predicate would be false, as the 70; final value of the expression {%Start,+,-1} expression (%M - 1) would not be 71; representable as an i16. 72 73; There is also a limit case here where the value of %M is MIN_INT. In this case 74; we still have an infinite loop, since icmp sge %x, MIN_INT will always return 75; true. 76 77; CHECK: Classifying expressions for: @test2 78 79; CHECK: %i.0.ext = sext i16 %i.0 to i32 80; CHECK-NEXT: --> (sext i16 {%Start,+,-1}<%bb3> to i32) 81; CHECK: Loop %bb3: Unpredictable backedge-taken count. 82; CHECK-NEXT: Loop %bb3: Unpredictable max backedge-taken count. 83; CHECK-NEXT: Loop %bb3: Predicated backedge-taken count is (2 + (sext i16 %Start to i32) + ((-2 + (-1 * (sext i16 %Start to i32))<nsw>) smax (-1 + (-1 * %M)))) 84; CHECK-NEXT: Predicates: 85; CHECK-NEXT: {%Start,+,-1}<%bb3> Added Flags: <nssw> 86 87define void @test2(i32 %N, i32 %M, i16 %Start) { 88entry: 89 br label %bb3 90 91bb: ; preds = %bb3 92 %tmp = getelementptr [1000 x i32], [1000 x i32]* @A, i32 0, i16 %i.0 ; <i32*> [#uses=1] 93 store i32 123, i32* %tmp 94 %tmp2 = sub i16 %i.0, 1 ; <i32> [#uses=1] 95 br label %bb3 96 97bb3: ; preds = %bb, %entry 98 %i.0 = phi i16 [ %Start, %entry ], [ %tmp2, %bb ] ; <i32> [#uses=3] 99 %i.0.ext = sext i16 %i.0 to i32 100 %tmp3 = icmp sge i32 %i.0.ext, %M ; <i1> [#uses=1] 101 br i1 %tmp3, label %bb, label %bb5 102 103bb5: ; preds = %bb3 104 br label %return 105 106return: ; preds = %bb5 107 ret void 108} 109 110