[PATCH] [AArch64] Implement getMaximumUnrollFactor()

[Z. Zheng]

Hi Jiangning, t.p.northover,

This patches allows vectorized loops to be unrolled by a factor of 2. Our experiments show this patch helps performance of linpack and a few tests in EEMBC.

http://reviews.llvm.org/D3320

Files:
  lib/Target/AArch64/AArch64TargetTransformInfo.cpp
  test/Transforms/LoopVectorize/AArch64/aarch64-unroll.ll

Index: lib/Target/AArch64/AArch64TargetTransformInfo.cpp
===================================================================
--- lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -92,6 +92,7 @@
     return 64;
   }
 
+  unsigned getMaximumUnrollFactor() const override { return 2; }
   /// @}
 };
 
Index: test/Transforms/LoopVectorize/AArch64/aarch64-unroll.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopVectorize/AArch64/aarch64-unroll.ll
@@ -0,0 +1,42 @@
+; RUN: opt < %s -loop-vectorize -mtriple=aarch64-none-linux-gnu -mattr=+neon -S | FileCheck %s
+target datalayout = "e-m:e-i64:64-i128:128-n32:64-S128"
+
+; Function Attrs: nounwind
+define i32* @array_add(i32* noalias nocapture readonly %a, i32* noalias nocapture readonly %b, i32* %c, i32 %size) {
+;CHECK-LABEL: array_add
+;CHECK: load <4 x i32>
+;CHECK: load <4 x i32>
+;CHECK: load <4 x i32>
+;CHECK: load <4 x i32>
+;CHECK: add nsw <4 x i32>
+;CHECK: add nsw <4 x i32>
+;CHECK: store <4 x i32>
+;CHECK: store <4 x i32>
+;CHECK: ret
+entry:
+  %cmp10 = icmp sgt i32 %size, 0
+  br i1 %cmp10, label %for.body.preheader, label %for.end
+
+for.body.preheader:                               ; preds = %entry
+  br label %for.body
+
+for.body:                                         ; preds = %for.body.preheader, %for.body
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %for.body.preheader ]
+  %arrayidx = getelementptr inbounds i32* %a, i64 %indvars.iv
+  %0 = load i32* %arrayidx, align 4
+  %arrayidx2 = getelementptr inbounds i32* %b, i64 %indvars.iv
+  %1 = load i32* %arrayidx2, align 4
+  %add = add nsw i32 %1, %0
+  %arrayidx4 = getelementptr inbounds i32* %c, i64 %indvars.iv
+  store i32 %add, i32* %arrayidx4, align 4
+  %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, %size
+  br i1 %exitcond, label %for.end.loopexit, label %for.body
+
+for.end.loopexit:                                 ; preds = %for.body
+  br label %for.end
+
+for.end:                                          ; preds = %for.end.loopexit, %entry
+  ret i32* %c
+}
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