1 ; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s 2 3 target 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> 28 define void @test1(i32 %N, i32 %M) { 29 entry: 30 br label %bb3 31 32 bb: ; 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 38 bb3: ; 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 44 bb5: ; preds = %bb3 45 br label %return 46 47 return: ; 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 87 define void @test2(i32 %N, i32 %M, i16 %Start) { 88 entry: 89 br label %bb3 90 91 bb: ; 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 97 bb3: ; 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 102 103 bb5: ; preds = %bb3 104 br label %return 105 106 return: ; preds = %bb5 107 ret void 108 } 109 110
