[llvm] r300441 - [LoopPeeling] Fix condition for phi-eliminating peeling

[Max Kazantsev via llvm-commits]

Author: mkazantsev
Date: Mon Apr 17 00:38:28 2017
New Revision: 300441

URL: http://llvm.org/viewvc/llvm-project?rev=300441&view=rev
Log:
[LoopPeeling] Fix condition for phi-eliminating peeling

When peeling loops basing on phis becoming invariants, we make a wrong loop size check.
UP.Threshold should be compared against the total numbers of instructions after the transformation,
which is equal to 2 * LoopSize in case of peeling one iteration.
We should also check that the maximum allowed number of peeled iterations is not zero.

Reviewers: sanjoy, anna, reames, mkuper

Reviewed By: mkuper

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31753

Added:
    llvm/trunk/test/Transforms/LoopUnroll/peel-loop-negative.ll
Modified:
    llvm/trunk/lib/Transforms/Utils/LoopUnrollPeel.cpp
    llvm/trunk/test/Transforms/LoopUnroll/peel-loop-not-forced.ll

Modified: llvm/trunk/lib/Transforms/Utils/LoopUnrollPeel.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopUnrollPeel.cpp?rev=300441&r1=300440&r2=300441&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/LoopUnrollPeel.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/LoopUnrollPeel.cpp Mon Apr 17 00:38:28 2017
@@ -82,7 +82,8 @@ void llvm::computePeelCount(Loop *L, uns
   // its only back edge. If there is such Phi, peeling 1 iteration from the
   // loop is profitable, because starting from 2nd iteration we will have an
   // invariant instead of this Phi.
-  if (LoopSize <= UP.Threshold) {
+  // First, check that we can peel at least one iteration.
+  if (2 * LoopSize <= UP.Threshold && UnrollPeelMaxCount > 0) {
     BasicBlock *BackEdge = L->getLoopLatch();
     assert(BackEdge && "Loop is not in simplified form?");
     BasicBlock *Header = L->getHeader();

Added: llvm/trunk/test/Transforms/LoopUnroll/peel-loop-negative.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/peel-loop-negative.ll?rev=300441&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopUnroll/peel-loop-negative.ll (added)
+++ llvm/trunk/test/Transforms/LoopUnroll/peel-loop-negative.ll Mon Apr 17 00:38:28 2017
@@ -0,0 +1,28 @@
+; RUN: opt < %s -S -loop-unroll -unroll-threshold=800 -unroll-peel-max-count=0 | FileCheck %s
+
+; We should not peel this loop even though we can, because the max count is set
+; to zero.
+define i32 @invariant_backedge_neg_1(i32 %a, i32 %b) {
+; CHECK-LABEL: @invariant_backedge_neg_1
+; CHECK-NOT    loop.peel{{.*}}:
+; CHECK:       loop:
+; CHECK:         %i = phi
+; CHECK:         %sum = phi
+; CHECK:         %plus = phi
+entry:
+  br label %loop
+
+loop:
+  %i = phi i32 [ 0, %entry ], [ %inc, %loop ]
+  %sum = phi i32 [ 0, %entry ], [ %incsum, %loop ]
+  %plus = phi i32 [ %a, %entry ], [ %b, %loop ]
+
+  %incsum = add i32 %sum, %plus
+  %inc = add i32 %i, 1
+  %cmp = icmp slt i32 %i, 1000
+
+  br i1 %cmp, label %loop, label %exit
+
+exit:
+  ret i32 %sum
+}

Modified: llvm/trunk/test/Transforms/LoopUnroll/peel-loop-not-forced.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/peel-loop-not-forced.ll?rev=300441&r1=300440&r2=300441&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopUnroll/peel-loop-not-forced.ll (original)
+++ llvm/trunk/test/Transforms/LoopUnroll/peel-loop-not-forced.ll Mon Apr 17 00:38:28 2017
@@ -1,4 +1,4 @@
-; RUN: opt < %s -S -loop-unroll -unroll-threshold=4 | FileCheck %s
+; RUN: opt < %s -S -loop-unroll -unroll-threshold=8 | FileCheck %s
 
 define i32 @invariant_backedge_1(i32 %a, i32 %b) {
 ; CHECK-LABEL: @invariant_backedge_1