Reapply [FastISel][AArch64] Make use of the zero register when possible (r215591).

Note: This was originally reverted to track down a buildbot error. Reapply
without any modifications.

Original commit message:
This change materializes now the value "0" from the zero register.
The zero register can be folded by several instruction, so no
materialization is need at all.

Fixes <rdar://problem/17924413>.

llvm-svn: 216009

llvm/lib/Target/AArch64/AArch64FastISel.cpp

@@ -217,7 +217,19 @@ unsigned AArch64FastISel::TargetMaterializeAlloca(const AllocaInst *AI) {
 unsigned AArch64FastISel::AArch64MaterializeInt(const ConstantInt *CI, MVT VT) {
   if (VT > MVT::i64)
     return 0;
-  return FastEmit_i(VT, VT, ISD::Constant, CI->getZExtValue());
+
+  if (!CI->isZero())
+    return FastEmit_i(VT, VT, ISD::Constant, CI->getZExtValue());
+
+  // Create a copy from the zero register to materialize a "0" value.
+  const TargetRegisterClass *RC = (VT == MVT::i64) ? &AArch64::GPR64RegClass
+                                                   : &AArch64::GPR32RegClass;
+  unsigned ZeroReg = (VT == MVT::i64) ? AArch64::XZR : AArch64::WZR;
+  unsigned ResultReg = createResultReg(RC);
+  BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc,
+          TII.get(TargetOpcode::COPY), ResultReg)
+    .addReg(ZeroReg, getKillRegState(true));
+  return ResultReg;
 }
 
 unsigned AArch64FastISel::AArch64MaterializeFP(const ConstantFP *CFP, MVT VT) {

llvm/test/CodeGen/AArch64/arm64-fast-isel-call.ll

@@ -42,7 +42,7 @@ entry:
 
 define i32 @sext_(i8 %a, i16 %b) nounwind {
 entry:
-; CHECK-LABEL: @sext_
+; CHECK-LABEL: sext_
 ; CHECK:       sxtb w0, w0
 ; CHECK:       sxth w1, w1
 ; CHECK:       bl _foo_sext_
@@ -54,7 +54,7 @@ declare void @foo_sext_(i8 %a, i16 %b)
 
 define i32 @zext_(i8 %a, i16 %b) nounwind {
 entry:
-; CHECK-LABEL: @zext_
+; CHECK-LABEL: zext_
 ; CHECK:       uxtb w0, w0
 ; CHECK:       uxth w1, w1
   call void @foo_zext_(i8 zeroext %a, i16 zeroext %b)
@@ -78,17 +78,18 @@ declare i32 @bar(i8 zeroext, i8 zeroext, i8 zeroext, i8 zeroext, i8 zeroext, i8
 ; Test materialization of integers.  Target-independent selector handles this.
 define i32 @t2() {
 entry:
-; CHECK-LABEL: @t2
-; CHECK:       movz x0, #0
+; CHECK-LABEL: t2
+; CHECK:       mov [[REG1:x[0-9]+]], xzr
 ; CHECK:       orr w1, wzr, #0xfffffff8
-; CHECK:       orr w[[REG:[0-9]+]], wzr, #0x3ff
-; CHECK:       orr w[[REG2:[0-9]+]], wzr, #0x2
-; CHECK:       movz w[[REG3:[0-9]+]], #0
-; CHECK:       orr w[[REG4:[0-9]+]], wzr, #0x1
-; CHECK:       uxth w2, w[[REG]]
-; CHECK:       sxtb w3, w[[REG2]]
-; CHECK:       and w4, w[[REG3]], #0x1
-; CHECK:       and w5, w[[REG4]], #0x1
+; CHECK:       orr [[REG2:w[0-9]+]], wzr, #0x3ff
+; CHECK:       orr [[REG3:w[0-9]+]], wzr, #0x2
+; CHECK:       mov [[REG4:w[0-9]+]], wzr
+; CHECK:       orr [[REG5:w[0-9]+]], wzr, #0x1
+; CHECK:       mov x0, [[REG1]]
+; CHECK:       uxth w2, [[REG2]]
+; CHECK:       sxtb w3, [[REG3]]
+; CHECK:       and w4, [[REG4]], #0x1
+; CHECK:       and w5, [[REG5]], #0x1
 ; CHECK:       bl _func2
   %call = call i32 @func2(i64 zeroext 0, i32 signext -8, i16 zeroext 1023, i8 signext -254, i1 zeroext 0, i1 zeroext 1)
   ret i32 0

llvm/test/CodeGen/AArch64/arm64-fast-isel-intrinsic.ll

@@ -7,7 +7,7 @@ define void @t1() {
 ; ARM64-LABEL: t1
 ; ARM64: adrp x8, _message@PAGE
 ; ARM64: add x0, x8, _message@PAGEOFF
-; ARM64: movz w9, #0
+; ARM64: mov w9, wzr
 ; ARM64: movz x2, #0x50
 ; ARM64: uxtb w1, w9
 ; ARM64: bl _memset

llvm/test/CodeGen/AArch64/arm64-fast-isel-store.ll

@@ -0,0 +1,30 @@
+; RUN: llc -mtriple=aarch64-unknown-unknown                             < %s | FileCheck %s
+; RUN: llc -mtriple=aarch64-unknown-unknown -fast-isel -fast-isel-abort < %s | FileCheck %s
+
+define void @store_i8(i8* %a) {
+; CHECK-LABEL: store_i8
+; CHECK: strb  wzr, [x0]
+  store i8 0, i8* %a
+  ret void
+}
+
+define void @store_i16(i16* %a) {
+; CHECK-LABEL: store_i16
+; CHECK: strh  wzr, [x0]
+  store i16 0, i16* %a
+  ret void
+}
+
+define void @store_i32(i32* %a) {
+; CHECK-LABEL: store_i32
+; CHECK: str  wzr, [x0]
+  store i32 0, i32* %a
+  ret void
+}
+
+define void @store_i64(i64* %a) {
+; CHECK-LABEL: store_i64
+; CHECK: str  xzr, [x0]
+  store i64 0, i64* %a
+  ret void
+}

llvm/test/CodeGen/AArch64/arm64-fast-isel.ll

@@ -66,7 +66,7 @@ entry:
 define void @t4(i32 *%ptr) nounwind {
 entry:
 ; CHECK-LABEL: t4:
-; CHECK: movz w8, #0
+; CHECK: mov w8, wzr
 ; CHECK: stur w8, [x0, #-4]
 ; CHECK: ret
   %0 = getelementptr i32 *%ptr, i32 -1
@@ -77,7 +77,7 @@ entry:
 define void @t5(i32 *%ptr) nounwind {
 entry:
 ; CHECK-LABEL: t5:
-; CHECK: movz w8, #0
+; CHECK: mov w8, wzr
 ; CHECK: stur w8, [x0, #-256]
 ; CHECK: ret
   %0 = getelementptr i32 *%ptr, i32 -64