[FastISel][AArch64] Optimize select when one of the operands is a 'true' or 'false' value.

Optimize selects of i1 in the presence of 'true' and 'false' operands to simple
logic operations.

This fixes rdar://problem/18960150.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221848 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/AArch64/AArch64FastISel.cpp

@@ -150,6 +150,7 @@ private:
   bool foldXALUIntrinsic(AArch64CC::CondCode &CC, const Instruction *I,
                          const Value *Cond);
   bool optimizeIntExtLoad(const Instruction *I, MVT RetVT, MVT SrcVT);
+  bool optimizeSelect(const SelectInst *SI);
 
   // Emit helper routines.
   unsigned emitAddSub(bool UseAdd, MVT RetVT, const Value *LHS,
@@ -2496,6 +2497,63 @@ bool AArch64FastISel::selectCmp(const Instruction *I) {
   return true;
 }
 
+/// \brief Optimize selects of i1 if one of the operands has a 'true' or 'false'
+/// value.
+bool AArch64FastISel::optimizeSelect(const SelectInst *SI) {
+  if (!SI->getType()->isIntegerTy(1))
+    return false;
+
+  const Value *Src1Val, *Src2Val;
+  unsigned Opc = 0;
+  bool NeedExtraOp = false;
+  if (auto *CI = dyn_cast<ConstantInt>(SI->getTrueValue())) {
+    if (CI->isOne()) {
+      Src1Val = SI->getCondition();
+      Src2Val = SI->getFalseValue();
+      Opc = AArch64::ORRWrr;
+    } else {
+      assert(CI->isZero());
+      Src1Val = SI->getFalseValue();
+      Src2Val = SI->getCondition();
+      Opc = AArch64::BICWrr;
+    }
+  } else if (auto *CI = dyn_cast<ConstantInt>(SI->getFalseValue())) {
+    if (CI->isOne()) {
+      Src1Val = SI->getCondition();
+      Src2Val = SI->getTrueValue();
+      Opc = AArch64::ORRWrr;
+      NeedExtraOp = true;
+    } else {
+      assert(CI->isZero());
+      Src1Val = SI->getCondition();
+      Src2Val = SI->getTrueValue();
+      Opc = AArch64::ANDWrr;
+    }
+  }
+
+  if (!Opc)
+    return false;
+
+  unsigned Src1Reg = getRegForValue(Src1Val);
+  if (!Src1Reg)
+    return false;
+  bool Src1IsKill = hasTrivialKill(Src1Val);
+
+  unsigned Src2Reg = getRegForValue(Src2Val);
+  if (!Src2Reg)
+    return false;
+  bool Src2IsKill = hasTrivialKill(Src2Val);
+
+  if (NeedExtraOp) {
+    Src1Reg = emitLogicalOp_ri(ISD::XOR, MVT::i32, Src1Reg, Src1IsKill, 1);
+    Src1IsKill = true;
+  }
+  unsigned ResultReg = fastEmitInst_rr(Opc, &AArch64::GPR32spRegClass, Src1Reg,
+                                       Src1IsKill, Src2Reg, Src2IsKill);
+  updateValueMap(SI, ResultReg);
+  return true;
+}
+
 bool AArch64FastISel::selectSelect(const Instruction *I) {
   assert(isa<SelectInst>(I) && "Expected a select instruction.");
   MVT VT;
@@ -2533,6 +2591,9 @@ bool AArch64FastISel::selectSelect(const Instruction *I) {
   AArch64CC::CondCode CC = AArch64CC::NE;
   AArch64CC::CondCode ExtraCC = AArch64CC::AL;
 
+  if (optimizeSelect(SI))
+    return true;
+
   // Try to pickup the flags, so we don't have to emit another compare.
   if (foldXALUIntrinsic(CC, I, Cond)) {
     // Fake request the condition to force emission of the XALU intrinsic.

test/CodeGen/AArch64/fast-isel-select.ll

@@ -284,3 +284,33 @@ define float @select_icmp_sle(i32 %x, i32 %y, float %a, float %b) {
   %2 = select i1 %1, float %a, float %b
   ret float %2
 }
+
+; Test peephole optimizations for select.
+define zeroext i1 @select_opt1(i1 zeroext %c, i1 zeroext %a) {
+; CHECK-LABEL: select_opt1
+; CHECK:       orr {{w[0-9]+}}, w0, w1
+  %1 = select i1 %c, i1 true, i1 %a
+  ret i1 %1
+}
+
+define zeroext i1 @select_opt2(i1 zeroext %c, i1 zeroext %a) {
+; CHECK-LABEL: select_opt2
+; CHECK:       eor [[REG:w[0-9]+]], w0, #0x1
+; CHECK:       orr {{w[0-9]+}}, [[REG]], w1
+  %1 = select i1 %c, i1 %a, i1 true
+  ret i1 %1
+}
+
+define zeroext i1 @select_opt3(i1 zeroext %c, i1 zeroext %a) {
+; CHECK-LABEL: select_opt3
+; CHECK:       bic {{w[0-9]+}}, w1, w0
+  %1 = select i1 %c, i1 false, i1 %a
+  ret i1 %1
+}
+
+define zeroext i1 @select_opt4(i1 zeroext %c, i1 zeroext %a) {
+; CHECK-LABEL: select_opt4
+; CHECK:       and {{w[0-9]+}}, w0, w1
+  %1 = select i1 %c, i1 %a, i1 false
+  ret i1 %1
+}