Re-enable "[SCEV] Make isLoopEntryGuardedByCond a bit smarter"

The failures happened because of assert which was overconfident about
SCEV's proving capabilities and is generally not valid.

Differential Revision: https://reviews.llvm.org/D42835

llvm-svn: 324473

1 files changed, 80 insertions, 0 deletions

diff --git a/llvm/test/Transforms/IRCE/decrementing-loop.ll b/llvm/test/Transforms/IRCE/decrementing-loop.ll
index fac873b4a24..e50479afe52 100644
--- a/llvm/test/Transforms/IRCE/decrementing-loop.ll
+++ b/llvm/test/Transforms/IRCE/decrementing-loop.ll
@@ -38,5 +38,85 @@ define void @decrementing_loop(i32 *%arr, i32 *%a_len_ptr, i32 %n) {
 ; CHECK:   %exit.preloop.at = add i32 [[not_exit_preloop_at]], -1
 }
 
+; Make sure that we can eliminate the range check when the loop looks like:
+; for (i = len.a - 1; i >= 0; --i)
+;   b[i] = a[i];
+define void @test_01(i32* %a, i32* %b, i32* %a_len_ptr, i32* %b_len_ptr) {
+
+; CHECK-LABEL: test_01
+; CHECK:       mainloop:
+; CHECK-NEXT:    br label %loop
+; CHECK:       loop:
+; CHECK:         %rc = and i1 true, true
+; CHECK:       loop.preloop:
+
+ entry:
+  %len.a = load i32, i32* %a_len_ptr, !range !0
+  %len.b = load i32, i32* %b_len_ptr, !range !0
+  %first.itr.check = icmp ne i32 %len.a, 0
+  br i1 %first.itr.check, label %loop, label %exit
+
+ loop:
+  %idx = phi i32 [ %len.a, %entry ] , [ %idx.next, %in.bounds ]
+  %idx.next = sub i32 %idx, 1
+  %rca = icmp ult i32 %idx.next, %len.a
+  %rcb = icmp ult i32 %idx.next, %len.b
+  %rc = and i1 %rca, %rcb
+  br i1 %rc, label %in.bounds, label %out.of.bounds, !prof !1
+
+ in.bounds:
+  %el.a = getelementptr i32, i32* %a, i32 %idx.next
+  %el.b = getelementptr i32, i32* %b, i32 %idx.next
+  %v = load i32, i32* %el.a
+  store i32 %v, i32* %el.b
+  %loop.cond = icmp slt i32 %idx, 2
+  br i1 %loop.cond, label %exit, label %loop
+
+ out.of.bounds:
+  ret void
+
+ exit:
+  ret void
+}
+
+; Same as test_01, but the latch condition is unsigned
+define void @test_02(i32* %a, i32* %b, i32* %a_len_ptr, i32* %b_len_ptr) {
+
+; CHECK-LABEL: test_02
+; CHECK:       mainloop:
+; CHECK-NEXT:    br label %loop
+; CHECK:       loop:
+; CHECK:         %rc = and i1 true, true
+; CHECK:       loop.preloop:
+
+ entry:
+  %len.a = load i32, i32* %a_len_ptr, !range !0
+  %len.b = load i32, i32* %b_len_ptr, !range !0
+  %first.itr.check = icmp ne i32 %len.a, 0
+  br i1 %first.itr.check, label %loop, label %exit
+
+ loop:
+  %idx = phi i32 [ %len.a, %entry ] , [ %idx.next, %in.bounds ]
+  %idx.next = sub i32 %idx, 1
+  %rca = icmp ult i32 %idx.next, %len.a
+  %rcb = icmp ult i32 %idx.next, %len.b
+  %rc = and i1 %rca, %rcb
+  br i1 %rc, label %in.bounds, label %out.of.bounds, !prof !1
+
+ in.bounds:
+  %el.a = getelementptr i32, i32* %a, i32 %idx.next
+  %el.b = getelementptr i32, i32* %b, i32 %idx.next
+  %v = load i32, i32* %el.a
+  store i32 %v, i32* %el.b
+  %loop.cond = icmp ult i32 %idx, 2
+  br i1 %loop.cond, label %exit, label %loop
+
+ out.of.bounds:
+  ret void
+
+ exit:
+  ret void
+}
+
 !0 = !{i32 0, i32 2147483647}
 !1 = !{!"branch_weights", i32 64, i32 4}