[llvm] r289583 - [LV] Don't vectorize when we have a small static bound on trip count

[Michael Kuperstein via llvm-commits]

Author: mkuper
Date: Tue Dec 13 14:38:18 2016
New Revision: 289583

URL: http://llvm.org/viewvc/llvm-project?rev=289583&view=rev
Log:
[LV] Don't vectorize when we have a small static bound on trip count

We currently check if the exact trip count is known and is smaller than the
"tiny loop" bound. We should be checking the maximum bound on the trip count
instead.

Differential Revision: https://reviews.llvm.org/D27690

Modified:
    llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
    llvm/trunk/test/Transforms/LoopVectorize/small-loop.ll

Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp?rev=289583&r1=289582&r2=289583&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Tue Dec 13 14:38:18 2016
@@ -7382,8 +7382,8 @@ bool LoopVectorizePass::processLoop(Loop
 
   // Check the loop for a trip count threshold:
   // do not vectorize loops with a tiny trip count.
-  const unsigned TC = SE->getSmallConstantTripCount(L);
-  if (TC > 0u && TC < TinyTripCountVectorThreshold) {
+  const unsigned MaxTC = SE->getSmallConstantMaxTripCount(L);
+  if (MaxTC > 0u && MaxTC < TinyTripCountVectorThreshold) {
     DEBUG(dbgs() << "LV: Found a loop with a very small trip count. "
                  << "This loop is not worth vectorizing.");
     if (Hints.getForce() == LoopVectorizeHints::FK_Enabled)

Modified: llvm/trunk/test/Transforms/LoopVectorize/small-loop.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/small-loop.ll?rev=289583&r1=289582&r2=289583&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/small-loop.ll (original)
+++ llvm/trunk/test/Transforms/LoopVectorize/small-loop.ll Tue Dec 13 14:38:18 2016
@@ -30,3 +30,28 @@ define void @example1() nounwind uwtable
   ret void
 }
 
+;CHECK-LABEL: @bound1(
+;CHECK-NOT: load <4 x i32>
+;CHECK: ret void
+define void @bound1(i32 %k) nounwind uwtable ssp {
+  br label %1
+
+; <label>:1                                       ; preds = %1, %0
+  %indvars.iv = phi i64 [ 0, %0 ], [ %indvars.iv.next, %1 ]
+  %2 = getelementptr inbounds [2048 x i32], [2048 x i32]* @b, i64 0, i64 %indvars.iv
+  %3 = load i32, i32* %2, align 4
+  %4 = getelementptr inbounds [2048 x i32], [2048 x i32]* @c, i64 0, i64 %indvars.iv
+  %5 = load i32, i32* %4, align 4
+  %6 = add nsw i32 %5, %3
+  %7 = getelementptr inbounds [2048 x i32], [2048 x i32]* @a, i64 0, i64 %indvars.iv
+  store i32 %6, i32* %7, align 4
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %large = icmp sge i32 %lftr.wideiv, 8
+  %exitcond = icmp eq i32 %lftr.wideiv, %k
+  %realexit = or i1 %large, %exitcond 
+  br i1 %realexit, label %8, label %1
+
+; <label>:8                                       ; preds = %1
+  ret void
+}