[llvm] 2d6aff8 - One more test case inspired by PR50191

[Philip Reames via llvm-commits]

Author: Philip Reames
Date: 2021-05-03T16:23:04-07:00
New Revision: 2d6aff84c9d7ab7babec3511197337467e3b3082

URL: https://github.com/llvm/llvm-project/commit/2d6aff84c9d7ab7babec3511197337467e3b3082
DIFF: https://github.com/llvm/llvm-project/commit/2d6aff84c9d7ab7babec3511197337467e3b3082.diff

LOG: One more test case inspired by PR50191

Added: 
    

Modified: 
    llvm/test/Analysis/ValueTracking/known-non-equal.ll

Removed: 
    


################################################################################
diff  --git a/llvm/test/Analysis/ValueTracking/known-non-equal.ll b/llvm/test/Analysis/ValueTracking/known-non-equal.ll
index 915ecf7f549d..c1a8f07953a3 100644
--- a/llvm/test/Analysis/ValueTracking/known-non-equal.ll
+++ b/llvm/test/Analysis/ValueTracking/known-non-equal.ll
@@ -1715,6 +1715,7 @@ exit:
   ret i1 %res
 }
 
+
 define i1 @mutual_recurrence_neq(i8 %A) {
 ; CHECK-LABEL: @mutual_recurrence_neq(
 ; CHECK-NEXT:  entry:
@@ -1779,5 +1780,42 @@ exit:
   ret i1 %res
 }
 
+; Illustrate a case where A_IV_i == B_IV_i for all i > 0, but A_IV_0 != B_IV_0.
+; (E.g. This pair of mutually defined recurrences are not invertible.)
+define i1 @recurrence_collapse(i8 %A) {
+; CHECK-LABEL: @recurrence_collapse(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[B:%.*]] = add i8 [[A:%.*]], 1
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[A_IV:%.*]] = phi i8 [ [[A]], [[ENTRY]] ], [ [[A_IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[B_IV:%.*]] = phi i8 [ [[B]], [[ENTRY]] ], [ [[B_IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
+; CHECK-NEXT:    [[A_IV_NEXT]] = sub i8 [[A_IV]], [[B_IV]]
+; CHECK-NEXT:    [[B_IV_NEXT]] = sub i8 [[A_IV]], [[B_IV]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i64 [[IV_NEXT]], 10
+; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[A_IV]], [[B_IV]]
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+entry:
+  %B = add i8 %A, 1
+  br label %loop
+loop:
+  %iv = phi i64 [0, %entry], [%iv.next, %loop]
+  %A.iv = phi i8 [%A, %entry], [%A.iv.next, %loop]
+  %B.iv = phi i8 [%B, %entry], [%B.iv.next, %loop]
+  %iv.next = add i64 %iv, 1
+  %A.iv.next = sub i8 %A.iv, %B.iv
+  %B.iv.next = sub i8 %A.iv, %B.iv
+  %cmp = icmp ne i64 %iv.next, 10
+  br i1 %cmp, label %loop, label %exit
+exit:
+  %res = icmp eq i8 %A.iv, %B.iv
+  ret i1 %res
+}
+
 
 !0 = !{ i8 1, i8 5 }