[AArch64] Improve cost model to handle sdiv by a pow-of-two.

This patch improves the target-specific cost model to better handle signed
division by a power of two. The immediate result is that this enables the SLP
vectorizer to do a better job.

http://reviews.llvm.org/D5469
PR20714

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218607 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
index abae09ba74062acdcf61b4c74d5a8e43fcef51c6..dbdf199a25cc4fb452adc95eee566f87a052530b 100644 (file)
--- a/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ b/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -413,6 +413,29 @@ unsigned AArch64TTI::getArithmeticInstrCost(
 
   int ISD = TLI->InstructionOpcodeToISD(Opcode);
 
+  if (ISD == ISD::SDIV &&
+      Opd2Info == TargetTransformInfo::OK_UniformConstantValue &&
+      Opd2PropInfo == TargetTransformInfo::OP_PowerOf2) {
+    // On AArch64, scalar signed division by constants power-of-two are
+    // normally expanded to the sequence ADD + CMP + SELECT + SRA.
+    // The OperandValue properties many not be same as that of previous
+    // operation; conservatively assume OP_None.
+    unsigned Cost =
+      getArithmeticInstrCost(Instruction::Add, Ty, Opd1Info, Opd2Info,
+                             TargetTransformInfo::OP_None,
+                             TargetTransformInfo::OP_None);
+    Cost += getArithmeticInstrCost(Instruction::Sub, Ty, Opd1Info, Opd2Info,
+                                   TargetTransformInfo::OP_None,
+                                   TargetTransformInfo::OP_None);
+    Cost += getArithmeticInstrCost(Instruction::Select, Ty, Opd1Info, Opd2Info,
+                                   TargetTransformInfo::OP_None,
+                                   TargetTransformInfo::OP_None);
+    Cost += getArithmeticInstrCost(Instruction::AShr, Ty, Opd1Info, Opd2Info,
+                                   TargetTransformInfo::OP_None,
+                                   TargetTransformInfo::OP_None);
+    return Cost;
+  }
+
   switch (ISD) {
   default:
     return TargetTransformInfo::getArithmeticInstrCost(

diff --git a/test/Transforms/SLPVectorizer/AArch64/sdiv-pow2.ll b/test/Transforms/SLPVectorizer/AArch64/sdiv-pow2.ll
new file mode 100644 (file)
index 0000000..e49c7ad
--- /dev/null
+++ b/test/Transforms/SLPVectorizer/AArch64/sdiv-pow2.ll
@@ -0,0 +1,42 @@
+; RUN: opt < %s -basicaa -slp-vectorizer -S -mtriple=aarch64-unknown-linux-gnu -mcpu=cortex-a57 | FileCheck %s
+target datalayout = "e-m:e-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64--linux-gnu"
+
+; CHECK-LABEL: @test1
+; CHECK: load <4 x i32>
+; CHECK: add nsw <4 x i32>
+; CHECK: sdiv <4 x i32>
+
+define void @test1(i32* noalias nocapture %a, i32* noalias nocapture readonly %b, i32* noalias nocapture readonly %c) {
+entry:
+  %0 = load i32* %b, align 4
+  %1 = load i32* %c, align 4
+  %add = add nsw i32 %1, %0
+  %div = sdiv i32 %add, 2
+  store i32 %div, i32* %a, align 4
+  %arrayidx3 = getelementptr inbounds i32* %b, i64 1
+  %2 = load i32* %arrayidx3, align 4
+  %arrayidx4 = getelementptr inbounds i32* %c, i64 1
+  %3 = load i32* %arrayidx4, align 4
+  %add5 = add nsw i32 %3, %2
+  %div6 = sdiv i32 %add5, 2
+  %arrayidx7 = getelementptr inbounds i32* %a, i64 1
+  store i32 %div6, i32* %arrayidx7, align 4
+  %arrayidx8 = getelementptr inbounds i32* %b, i64 2
+  %4 = load i32* %arrayidx8, align 4
+  %arrayidx9 = getelementptr inbounds i32* %c, i64 2
+  %5 = load i32* %arrayidx9, align 4
+  %add10 = add nsw i32 %5, %4
+  %div11 = sdiv i32 %add10, 2
+  %arrayidx12 = getelementptr inbounds i32* %a, i64 2
+  store i32 %div11, i32* %arrayidx12, align 4
+  %arrayidx13 = getelementptr inbounds i32* %b, i64 3
+  %6 = load i32* %arrayidx13, align 4
+  %arrayidx14 = getelementptr inbounds i32* %c, i64 3
+  %7 = load i32* %arrayidx14, align 4
+  %add15 = add nsw i32 %7, %6
+  %div16 = sdiv i32 %add15, 2
+  %arrayidx17 = getelementptr inbounds i32* %a, i64 3
+  store i32 %div16, i32* %arrayidx17, align 4
+  ret void
+}