[llvm-commits] [llvm] r122711 - in /llvm/trunk: lib/Transforms/Scalar/LoopIdiomRecognize.cpp test/Transforms/LoopIdiom/basic.ll

[Chris Lattner]

Author: lattner
Date: Sun Jan  2 14:24:21 2011
New Revision: 122711

URL: http://llvm.org/viewvc/llvm-project?rev=122711&view=rev
Log:
If a loop iterates exactly once (has backedge count = 0) then don't
mess with it.  We'd rather peel/unroll it than convert all of its 
stores into memsets.

Modified:
    llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
    llvm/trunk/test/Transforms/LoopIdiom/basic.ll

Modified: llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp?rev=122711&r1=122710&r2=122711&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp Sun Jan  2 14:24:21 2011
@@ -159,6 +159,12 @@
   const SCEV *BECount = SE->getBackedgeTakenCount(L);
   if (isa<SCEVCouldNotCompute>(BECount)) return false;
   
+  // If this loop executes exactly one time, then it should be peeled, not
+  // optimized by this pass.
+  if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
+    if (BECst->getValue()->getValue() == 0)
+      return false;
+  
   // We require target data for now.
   TD = getAnalysisIfAvailable<TargetData>();
   if (TD == 0) return false;

Modified: llvm/trunk/test/Transforms/LoopIdiom/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopIdiom/basic.ll?rev=122711&r1=122710&r2=122711&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopIdiom/basic.ll (original)
+++ llvm/trunk/test/Transforms/LoopIdiom/basic.ll Sun Jan  2 14:24:21 2011
@@ -188,4 +188,22 @@
 ; CHECK-NOT: store
 }
 
+; This is a loop should not be transformed, it only executes one iteration.
+define void @test8(i64* %Ptr, i64 %Size) nounwind ssp {
+bb.nph:                                           ; preds = %entry
+  br label %for.body
+
+for.body:                                         ; preds = %bb.nph, %for.body
+  %indvar = phi i64 [ 0, %bb.nph ], [ %indvar.next, %for.body ]
+  %PI = getelementptr i64* %Ptr, i64 %indvar
+  store i64 0, i64 *%PI
+  %indvar.next = add i64 %indvar, 1
+  %exitcond = icmp eq i64 %indvar.next, 1
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body, %entry
+  ret void
+; CHECK: @test8
+; CHECK: store i64 0, i64* %PI
+}