[IRCE] Add a missing invariant check

Currently IRCE relies on the loops it transforms to be (semantically) of
the form:

  for (i = START; i < END; i++)
    ...

or

  for (i = START; i > END; i--)
    ...

However, we were not verifying the presence of the START < END entry
check (i.e. check before the first iteration).  We were only verifying
that the backedge was guarded by (i + 1) < END.

Usually this would work "fine" since (especially in Java) most loops do
actually have the START < END check, but of course that is not
guaranteed.

llvm-svn: 294375

1 files changed, 45 insertions, 0 deletions

diff --git a/llvm/test/Transforms/IRCE/bad-loop-structure.ll b/llvm/test/Transforms/IRCE/bad-loop-structure.ll
new file mode 100644
index 00000000000..9c2e4251423
--- /dev/null
+++ b/llvm/test/Transforms/IRCE/bad-loop-structure.ll
@@ -0,0 +1,45 @@
+; RUN: opt -S -irce -irce-print-changed-loops=true < %s | FileCheck %s
+
+; CHECK-NOT: irce
+
+define void @bad_loop_structure_increasing(i64 %iv.start) {
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ %iv.start, %entry ], [ %indvars.iv.next, %for.inc ]
+  %cmp = icmp ult i64 %indvars.iv, 100
+  br i1 %cmp, label %switch.lookup, label %for.inc
+
+switch.lookup:
+  br label %for.inc
+
+for.inc:
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %cmp55 = icmp slt i64 %indvars.iv.next, 11
+  br i1 %cmp55, label %for.body, label %for.end
+
+for.end:
+  ret void
+}
+
+define void @bad_loop_structure_decreasing(i64 %iv.start) {
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ %iv.start, %entry ], [ %indvars.iv.next, %for.inc ]
+  %cmp = icmp ult i64 %indvars.iv, 100
+  br i1 %cmp, label %switch.lookup, label %for.inc
+
+switch.lookup:
+  br label %for.inc
+
+for.inc:
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, -1
+  %cmp55 = icmp sgt i64 %indvars.iv.next, 11
+  br i1 %cmp55, label %for.body, label %for.end
+
+for.end:
+  ret void
+}