[llvm] r207940 - LoopUnroll: If we're doing partial unrolling, use the PartialThreshold to limit unrolling.

[Benjamin Kramer]

Author: d0k
Date: Sun May  4 14:12:38 2014
New Revision: 207940

URL: http://llvm.org/viewvc/llvm-project?rev=207940&view=rev
Log:
LoopUnroll: If we're doing partial unrolling, use the PartialThreshold to limit unrolling.

Otherwise we use the same threshold as for complete unrolling, which is
way too high. This made us unroll any loop smaller than 150 instructions
by 8 times, but only if someone specified -march=core2 or better,
which happens to be the default on darwin.

Modified:
    llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
    llvm/trunk/test/Transforms/LoopUnroll/X86/partial.ll

Modified: llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp?rev=207940&r1=207939&r2=207940&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp Sun May  4 14:12:38 2014
@@ -238,9 +238,12 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPa
       return false;
     }
     uint64_t Size = (uint64_t)LoopSize*Count;
-    if (TripCount != 1 && Size > Threshold) {
-      DEBUG(dbgs() << "  Too large to fully unroll with count: " << Count
-            << " because size: " << Size << ">" << Threshold << "\n");
+    if (TripCount != 1 &&
+        (Size > Threshold || (Count != TripCount && Size > PartialThreshold))) {
+      if (Size > Threshold)
+        DEBUG(dbgs() << "  Too large to fully unroll with count: " << Count
+                     << " because size: " << Size << ">" << Threshold << "\n");
+
       bool AllowPartial = UserAllowPartial ? CurrentAllowPartial : UP.Partial;
       if (!AllowPartial && !(Runtime && TripCount == 0)) {
         DEBUG(dbgs() << "  will not try to unroll partially because "

Modified: llvm/trunk/test/Transforms/LoopUnroll/X86/partial.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/X86/partial.ll?rev=207940&r1=207939&r2=207940&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopUnroll/X86/partial.ll (original)
+++ llvm/trunk/test/Transforms/LoopUnroll/X86/partial.ll Sun May  4 14:12:38 2014
@@ -76,5 +76,52 @@ for.end:
   ret void
 }
 
+define zeroext i16 @test1(i16* nocapture readonly %arr, i32 %n) #0 {
+entry:
+  %cmp25 = icmp eq i32 %n, 0
+  br i1 %cmp25, label %for.end, label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
+  %reduction.026 = phi i16 [ %add14, %for.body ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i16* %arr, i64 %indvars.iv
+  %0 = load i16* %arrayidx, align 2
+  %add = add i16 %0, %reduction.026
+  %sext = mul i64 %indvars.iv, 12884901888
+  %idxprom3 = ashr exact i64 %sext, 32
+  %arrayidx4 = getelementptr inbounds i16* %arr, i64 %idxprom3
+  %1 = load i16* %arrayidx4, align 2
+  %add7 = add i16 %add, %1
+  %sext28 = mul i64 %indvars.iv, 21474836480
+  %idxprom10 = ashr exact i64 %sext28, 32
+  %arrayidx11 = getelementptr inbounds i16* %arr, i64 %idxprom10
+  %2 = load i16* %arrayidx11, align 2
+  %add14 = add i16 %add7, %2
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body, %entry
+  %reduction.0.lcssa = phi i16 [ 0, %entry ], [ %add14, %for.body ]
+  ret i16 %reduction.0.lcssa
+
+; This loop is too large to be partially unrolled (size=16)
+
+; CHECK-LABEL: @test1
+; CHECK: br
+; CHECK: br
+; CHECK: br
+; CHECK: br
+; CHECK-NOT: br
+
+; CHECK-NOUNRL-LABEL: @test1
+; CHECK-NOUNRL: br
+; CHECK-NOUNRL: br
+; CHECK-NOUNRL: br
+; CHECK-NOUNRL: br
+; CHECK-NOUNRL-NOT: br
+}
+
 attributes #0 = { nounwind uwtable }