[PATCH] Choose the best consecutive candidate for a store instruction in SLP vectorizer

[Wei Mi]

Hi nadav, aschwaighofer,

This is the following patch for http://reviews.llvm.org/D10352. It changes the SLPVectorizer::vectorizeStores to choose the immediate succeeding or preceding candidate for a store instruction when it has multiple consecutive candidates. This way, it has better chance to find the slp vectorization opportunity.

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D10445

Files:
  lib/Transforms/Vectorize/SLPVectorizer.cpp
  test/Transforms/SLPVectorizer/X86/pr23510.ll

Index: lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -3244,14 +3244,26 @@
   // Do a quadratic search on all of the given stores and find
   // all of the pairs of stores that follow each other.
   for (unsigned i = 0, e = Stores.size(); i < e; ++i) {
-    for (unsigned j = 0; j < e; ++j) {
-      if (i == j)
-        continue;
-      const DataLayout &DL = Stores[i]->getModule()->getDataLayout();
+    const DataLayout &DL = Stores[i]->getModule()->getDataLayout();
+    unsigned j;
+    // If a store has multiple consectutive store candidates, choose
+    // the immediate succeeding or preceding one.
+    for (j = i + 1; j < e; ++j) {
+      if (R.isConsecutiveAccess(Stores[i], Stores[j], DL)) {
+        Tails.insert(Stores[j]);
+        Heads.insert(Stores[i]);
+        ConsecutiveChain[Stores[i]] = Stores[j];
+        break;
+      }
+    }
+    if (j < e)
+      continue;
+    for (int j = i - 1; j >= 0; --j) {
       if (R.isConsecutiveAccess(Stores[i], Stores[j], DL)) {
         Tails.insert(Stores[j]);
         Heads.insert(Stores[i]);
         ConsecutiveChain[Stores[i]] = Stores[j];
+        break;
       }
     }
   }
Index: test/Transforms/SLPVectorizer/X86/pr23510.ll
===================================================================
--- test/Transforms/SLPVectorizer/X86/pr23510.ll
+++ test/Transforms/SLPVectorizer/X86/pr23510.ll
@@ -0,0 +1,37 @@
+; PR23510
+; RUN: opt < %s -basicaa -slp-vectorizer -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK: lshr <2 x i64>
+; CHECK: lshr <2 x i64>
+
+ at total = global i64 0, align 8
+
+define void @_Z3fooPml(i64* nocapture %a, i64 %i) {
+entry:
+  %tmp = load i64, i64* %a, align 8
+  %shr = lshr i64 %tmp, 4
+  store i64 %shr, i64* %a, align 8
+  %arrayidx1 = getelementptr inbounds i64, i64* %a, i64 1
+  %tmp1 = load i64, i64* %arrayidx1, align 8
+  %shr2 = lshr i64 %tmp1, 4
+  store i64 %shr2, i64* %arrayidx1, align 8
+  %arrayidx3 = getelementptr inbounds i64, i64* %a, i64 %i
+  %tmp2 = load i64, i64* %arrayidx3, align 8
+  %tmp3 = load i64, i64* @total, align 8
+  %add = add i64 %tmp3, %tmp2
+  store i64 %add, i64* @total, align 8
+  %tmp4 = load i64, i64* %a, align 8
+  %shr5 = lshr i64 %tmp4, 4
+  store i64 %shr5, i64* %a, align 8
+  %tmp5 = load i64, i64* %arrayidx1, align 8
+  %shr7 = lshr i64 %tmp5, 4
+  store i64 %shr7, i64* %arrayidx1, align 8
+  %tmp6 = load i64, i64* %arrayidx3, align 8
+  %tmp7 = load i64, i64* @total, align 8
+  %add9 = add i64 %tmp7, %tmp6
+  store i64 %add9, i64* @total, align 8
+  ret void
+}

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