From: Sanjoy Das <sanjoy@playingwithpointers.com>
Date: Sun, 12 Apr 2015 01:24:01 +0000 (+0000)
Subject: [LoopUnrollRuntime] Clean up a predicate.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=e0f4a11a8971f0f736dec8392a066081753e26cd;p=oota-llvm.git

[LoopUnrollRuntime] Clean up a predicate.

Clean up a predicate I added in r229731, fix the relevant comment and
add a test case.  The earlier version is confusing to read and was also
buggy (probably not a coincidence) till Alexey fixed it in r233881.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234701 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Utils/LoopUnrollRuntime.cpp b/lib/Transforms/Utils/LoopUnrollRuntime.cpp
index 46570a11a4f..c8d47828eba 100644
--- a/lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ b/lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -318,9 +318,8 @@ bool llvm::UnrollRuntimeLoopProlog(Loop *L, unsigned Count, LoopInfo *LI,
     return false;
 
   // This constraint lets us deal with an overflowing trip count easily; see the
-  // comment on ModVal below.  This check is equivalent to `Log2(Count) <
-  // BEWidth`.
-  if (BEWidth < 64 && static_cast<uint64_t>(Count) > (1ULL << BEWidth))
+  // comment on ModVal below.
+  if (Log2_32(Count) > BEWidth)
     return false;
 
   // If this loop is nested, then the loop unroller changes the code in
diff --git a/test/Transforms/LoopUnroll/runtime-loop5.ll b/test/Transforms/LoopUnroll/runtime-loop5.ll
new file mode 100644
index 00000000000..e8d51775ce1
--- /dev/null
+++ b/test/Transforms/LoopUnroll/runtime-loop5.ll
@@ -0,0 +1,45 @@
+; RUN: opt < %s -S -loop-unroll -unroll-runtime=true -unroll-count=16 | FileCheck --check-prefix=UNROLL-16 %s
+; RUN: opt < %s -S -loop-unroll -unroll-runtime=true -unroll-count=4 | FileCheck --check-prefix=UNROLL-4 %s
+
+; Given that the trip-count of this loop is a 3-bit value, we cannot
+; safely unroll it with a count of anything more than 8.
+
+define i3 @test(i3* %a, i3 %n) {
+; UNROLL-16-LABEL: @test(
+; UNROLL-4-LABEL: @test(
+entry:
+  %cmp1 = icmp eq i3 %n, 0
+  br i1 %cmp1, label %for.end, label %for.body
+
+; UNROLL-16-NOT: for.body.prol:
+; UNROLL-4: for.body.prol:
+
+for.body:                                         ; preds = %for.body, %entry
+; UNROLL-16-LABEL: for.body:
+; UNROLL-4-LABEL: for.body:
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
+  %sum.02 = phi i3 [ %add, %for.body ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i3, i3* %a, i64 %indvars.iv
+
+; UNROLL-16-LABEL: for.body
+; UNROLL-16-LABEL: getelementptr
+; UNROLL-16-LABEL-NOT: getelementptr
+
+; UNROLL-4-LABEL: getelementptr
+; UNROLL-4-LABEL: getelementptr
+; UNROLL-4-LABEL: getelementptr
+; UNROLL-4-LABEL: getelementptr
+
+  %0 = load i3, i3* %arrayidx
+  %add = add nsw i3 %0, %sum.02
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i3
+  %exitcond = icmp eq i3 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.end, label %for.body
+
+; UNROLL-16-LABEL: for.end
+; UNROLL-4-LABEL: for.end
+for.end:                                          ; preds = %for.body, %entry
+  %sum.0.lcssa = phi i3 [ 0, %entry ], [ %add, %for.body ]
+  ret i3 %sum.0.lcssa
+}