1 files changed, 109 insertions, 0 deletions
diff --git a/llvm/test/Analysis/ScalarEvolution/predicated-trip-count.ll b/llvm/test/Analysis/ScalarEvolution/predicated-trip-count.ll
new file mode 100644
index 00000000000..2db0a8b5777
--- /dev/null
+++ b/llvm/test/Analysis/ScalarEvolution/predicated-trip-count.ll
@@ -0,0 +1,109 @@
+; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+@A = weak global [1000 x i32] zeroinitializer, align 32
+
+; The resulting predicate is i16 {0,+,1} <nssw>, meanining
+; that the resulting backedge expression will be valid for:
+;   (1 + (-1 smax %M)) <= MAX_INT16
+;
+; At the limit condition for M (MAX_INT16 - 1) we have in the
+; last iteration:
+;    i0 <- MAX_INT16
+;    i0.ext <- MAX_INT16
+;
+; and therefore no wrapping happend for i0 or i0.ext
+; throughout the execution of the loop. The resulting predicated
+; backedge taken count is correct.
+
+; CHECK: Classifying expressions for: @test1
+; CHECK: %i.0.ext = sext i16 %i.0 to i32
+; CHECK-NEXT:  -->  (sext i16 {0,+,1}<%bb3> to i32)
+; CHECK:      Loop %bb3: Unpredictable backedge-taken count.
+; CHECK-NEXT: Loop %bb3: Unpredictable max backedge-taken count.
+; CHECK-NEXT: Loop %bb3: Predicated backedge-taken count is (1 + (-1 smax %M))
+; CHECK-NEXT: Predicates:
+; CHECK-NEXT:    {0,+,1}<%bb3> Added Flags: <nssw>
+define void @test1(i32 %N, i32 %M) {
+entry:
+        br label %bb3
+
+bb:             ; preds = %bb3
+        %tmp = getelementptr [1000 x i32], [1000 x i32]* @A, i32 0, i16 %i.0          ; <i32*> [#uses=1]
+        store i32 123, i32* %tmp
+        %tmp2 = add i16 %i.0, 1         ; <i32> [#uses=1]
+        br label %bb3
+
+bb3:            ; preds = %bb, %entry
+        %i.0 = phi i16 [ 0, %entry ], [ %tmp2, %bb ]            ; <i32> [#uses=3]
+        %i.0.ext = sext i16 %i.0 to i32
+        %tmp3 = icmp sle i32 %i.0.ext, %M          ; <i1> [#uses=1]
+        br i1 %tmp3, label %bb, label %bb5
+
+bb5:            ; preds = %bb3
+        br label %return
+
+return:         ; preds = %bb5
+        ret void
+}
+
+; The predicated backedge taken count is:
+;    (2 + (zext i16 %Start to i32) + ((-2 + (-1 * (sext i16 %Start to i32)))
+;                                     smax (-1 + (-1 * %M)))
+;    )
+
+; -1 + (-1 * %M) <= (-2 + (-1 * (sext i16 %Start to i32))
+; The predicated backedge taken count is 0.
+; From the IR, this is correct since we will bail out at the
+; first iteration.
+
+
+; * -1 + (-1 * %M) > (-2 + (-1 * (sext i16 %Start to i32))
+; or: %M < 1 + (sext i16 %Start to i32)
+;
+; The predicated backedge taken count is 1 + (zext i16 %Start to i32) - %M
+;
+; If %M >= MIN_INT + 1, this predicated backedge taken count would be correct (even
+; without predicates). However, for %M < MIN_INT this would be an infinite loop.
+; In these cases, the {%Start,+,-1} <nusw> predicate would be false, as the
+; final value of the expression {%Start,+,-1} expression (%M - 1) would not be
+; representable as an i16.
+
+; There is also a limit case here where the value of %M is MIN_INT. In this case
+; we still have an infinite loop, since icmp sge %x, MIN_INT will always return
+; true.
+
+; CHECK: Classifying expressions for: @test2
+
+; CHECK:      %i.0.ext = sext i16 %i.0 to i32
+; CHECK-NEXT:    -->  (sext i16 {%Start,+,-1}<%bb3> to i32)
+; CHECK:       Loop %bb3: Unpredictable backedge-taken count.
+; CHECK-NEXT:  Loop %bb3: Unpredictable max backedge-taken count.
+; CHECK-NEXT:  Loop %bb3: Predicated backedge-taken count is (2 + (sext i16 %Start to i32) + ((-2 + (-1 * (sext i16 %Start to i32))) smax (-1 + (-1 * %M))))
+; CHECK-NEXT:  Predicates:
+; CHECK-NEXT:    {%Start,+,-1}<%bb3> Added Flags: <nssw>
+
+define void @test2(i32 %N, i32 %M, i16 %Start) {
+entry:
+        br label %bb3
+
+bb:             ; preds = %bb3
+        %tmp = getelementptr [1000 x i32], [1000 x i32]* @A, i32 0, i16 %i.0          ; <i32*> [#uses=1]
+        store i32 123, i32* %tmp
+        %tmp2 = sub i16 %i.0, 1         ; <i32> [#uses=1]
+        br label %bb3
+
+bb3:            ; preds = %bb, %entry
+        %i.0 = phi i16 [ %Start, %entry ], [ %tmp2, %bb ]            ; <i32> [#uses=3]
+        %i.0.ext = sext i16 %i.0 to i32
+        %tmp3 = icmp sge i32 %i.0.ext, %M          ; <i1> [#uses=1]
+        br i1 %tmp3, label %bb, label %bb5
+
+bb5:            ; preds = %bb3
+        br label %return
+
+return:         ; preds = %bb5
+        ret void
+}
+