[ScalarEvolution] Handling for ICmp occuring in the evolution chain.

Summary:
 If a compare instruction is same or inverse of the compare in the
 branch of the loop latch, then return a constant evolution node.
 Currently scope of evaluation is limited to SCEV computation for
 PHI nodes.

 This shall facilitate computations of loop exit counts in cases
 where compare appears in the evolution chain of induction variables.

 Will fix PR 34538
Reviewers: sanjoy, hfinkel, junryoungju

Reviewed By: junryoungju

Subscribers: javed.absar, llvm-commits

Differential Revision: https://reviews.llvm.org/D38494

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316054 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 19 insertions, 0 deletions

diff --git a/test/Analysis/ScalarEvolution/pr34538.ll b/test/Analysis/ScalarEvolution/pr34538.ll
new file mode 100644
index 00000000000..0aa72c36de4
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/pr34538.ll
@@ -0,0 +1,19 @@
+; RUN: opt -S -scalar-evolution -loop-deletion -simplifycfg -analyze < %s | FileCheck %s --check-prefix=CHECK-ANALYSIS
+
+define i32 @foo() local_unnamed_addr #0 {
+; CHECK-ANALYSIS: Loop %do.body: backedge-taken count is 10000
+; CHECK-ANALYSIS: Loop %do.body: max backedge-taken count is 10000
+; CHECK-ANALYSIS: Loop %do.body: Predicated backedge-taken count is 10000
+entry:
+  br label %do.body
+
+do.body:                                          ; preds = %do.body, %entry
+  %start.0 = phi i32 [ 0, %entry ], [ %inc.start.0, %do.body ]
+  %cmp = icmp slt i32 %start.0, 10000
+  %inc = zext i1 %cmp to i32
+  %inc.start.0 = add nsw i32 %start.0, %inc
+  br i1 %cmp, label %do.body, label %do.end
+
+do.end:                                           ; preds = %do.body
+  ret i32 0
+}