[NFC] Remove overconfident assert from IRCE

This patch removes assert that SCEV is able to prove that a value is
non-negative. In fact, SCEV can sometimes be unable to do this because
its cache does not update properly. This assert will be returned once this
problem is resolved.

llvm-svn: 323309

lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp

@@ -1643,8 +1643,6 @@ InductiveRangeCheck::computeSafeIterationSpace(
   // values, depending on type of latch condition that defines IV iteration
   // space.
   auto ClampedSubstract = [&](const SCEV *X, const SCEV *Y) {
-    assert(SE.isKnownNonNegative(X) &&
-           "We can only substract from values in [0; SINT_MAX]!");
     if (IsLatchSigned) {
       // X is a number from signed range, Y is interpreted as signed.
       // Even if Y is SINT_MAX, (X - Y) does not reach SINT_MIN. So the only

test/Transforms/IRCE/optimistic_scev.ll

@@ -0,0 +1,42 @@
+; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -S < %s 2>&1 | FileCheck %s
+
+; CHECK-LABEL: irce: in function test_01: constrained Loop at depth 2 containing:
+
+define void @test_01(i64 %len) {
+
+; CHECK-LABEL: @test_01(
+
+entry:
+  br label %loop
+
+check:
+  %entry_check = icmp eq i32 %idx.next, 0
+  br i1 %entry_check, label %exit, label %loop
+
+loop:
+  %idx = phi i32 [ 1, %entry ], [ %idx.next, %check ]
+  %idx_ext = sext i32 %idx to i64
+  br label %inner_loop
+
+inner_loop:
+  %iv = phi i64 [ 0, %loop ], [ %iv.next, %inner_backedge ]
+  %iv.next = add nuw nsw i64 %iv, 1
+  %inner_check = icmp slt i64 %iv.next, %idx_ext
+  br i1 %inner_check, label %inner, label %outer_check
+
+inner:
+  %iv_next_check = icmp slt i64 %iv.next, 100
+  br i1 %iv_next_check, label %inner_backedge, label %exit
+
+inner_backedge:
+  %cond = icmp eq i64 %iv.next, 100
+  br i1 %cond, label %exit, label %inner_loop
+
+outer_check:
+  %idx.next = add i32 %idx, 1
+  %loopdone = icmp slt i32 %idx.next, 2
+  br i1 %loopdone, label %check, label %exit
+
+exit:
+  ret void
+}