[AArch64] Do not lower scalar sdiv/udiv to a shifts + mul sequence when optimizing for minsize

Mimic what x86 does when optimizing sdiv/udiv for minsize.

llvm-svn: 264606

2 files changed, 19 insertions, 0 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index c35fa4df757..a262b1d2b3f 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -7516,6 +7516,10 @@ SDValue
 AArch64TargetLowering::BuildSDIVPow2(SDNode *N, const APInt &Divisor,
                                      SelectionDAG &DAG,
                                      std::vector<SDNode *> *Created) const {
+  AttributeSet Attr = DAG.getMachineFunction().getFunction()->getAttributes();
+  if (isIntDivCheap(N->getValueType(0), Attr))
+    return SDValue(N,0); // Lower SDIV as SDIV
+
   // fold (sdiv X, pow2)
   EVT VT = N->getValueType(0);
   if ((VT != MVT::i32 && VT != MVT::i64) ||
@@ -10298,3 +10302,16 @@ void AArch64TargetLowering::insertCopiesSplitCSR(
           .addReg(NewVR);
   }
 }
+
+bool AArch64TargetLowering::isIntDivCheap(EVT VT, AttributeSet Attr) const {
+  // Integer division on AArch64 is expensive. However, when aggressively
+  // optimizing for code size, we prefer to use a div instruction, as it is
+  // usually smaller than the alternative sequence.
+  // The exception to this is vector division. Since AArch64 doesn't have vector
+  // integer division, leaving the division as-is is a loss even in terms of
+  // size, because it will have to be scalarized, while the alternative code
+  // sequence can be performed in vector form.
+  bool OptSize =
+      Attr.hasAttribute(AttributeSet::FunctionIndex, Attribute::MinSize);
+  return OptSize && !VT.isVector();
+}
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.h b/llvm/lib/Target/AArch64/AArch64ISelLowering.h
index 20c468e08de..13eba096142 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.h
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.h
@@ -378,6 +378,8 @@ public:
     return AArch64::X1;
   }
 
+  bool isIntDivCheap(EVT VT, AttributeSet Attr) const override;
+
   bool isCheapToSpeculateCttz() const override {
     return true;
   }