[AArch64] Improve lowering of GPR zeroing in copyPhysReg

This patch pivots GPR32 and GPR64 zeroing into distinct branches to simplify the code an improve the lowering.

Zeroing GPR moves are now handled differently than non-zeroing ones. Zero source registers WZR and XZR do not require register annotations of undef, implicit and kill. The non-zeroing source now cannot process WZR removing the ternary expression. This patch also moves GPR64 logic right after GPR32 for better organization.

Author: tomershafir

llvm/lib/Target/AArch64/AArch64InstrInfo.cpp

@@ -5063,7 +5063,7 @@ void AArch64InstrInfo::copyPhysReg(MachineBasicBlock &MBB,
                                    bool RenamableDest,
                                    bool RenamableSrc) const {
   if (AArch64::GPR32spRegClass.contains(DestReg) &&
-      (AArch64::GPR32spRegClass.contains(SrcReg) || SrcReg == AArch64::WZR)) {
+      AArch64::GPR32spRegClass.contains(SrcReg)) {
     if (DestReg == AArch64::WSP || SrcReg == AArch64::WSP) {
       // If either operand is WSP, expand to ADD #0.
       if (Subtarget.hasZeroCycleRegMoveGPR64() &&
@@ -5088,21 +5088,14 @@ void AArch64InstrInfo::copyPhysReg(MachineBasicBlock &MBB,
             .addImm(0)
             .addImm(AArch64_AM::getShifterImm(AArch64_AM::LSL, 0));
       }
-    } else if (SrcReg == AArch64::WZR && Subtarget.hasZeroCycleZeroingGPR32()) {
-      BuildMI(MBB, I, DL, get(AArch64::MOVZWi), DestReg)
-          .addImm(0)
-          .addImm(AArch64_AM::getShifterImm(AArch64_AM::LSL, 0));
     } else if (Subtarget.hasZeroCycleRegMoveGPR64() &&
                !Subtarget.hasZeroCycleRegMoveGPR32()) {
       // Cyclone recognizes "ORR Xd, XZR, Xm" as a zero-cycle register move.
       MCRegister DestRegX = RI.getMatchingSuperReg(DestReg, AArch64::sub_32,
                                                    &AArch64::GPR64spRegClass);
       assert(DestRegX.isValid() && "Destination super-reg not valid");
-      MCRegister SrcRegX =
-          SrcReg == AArch64::WZR
-              ? AArch64::XZR
-              : RI.getMatchingSuperReg(SrcReg, AArch64::sub_32,
-                                       &AArch64::GPR64spRegClass);
+      MCRegister SrcRegX = RI.getMatchingSuperReg(SrcReg, AArch64::sub_32,
+                                                  &AArch64::GPR64spRegClass);
       assert(SrcRegX.isValid() && "Source super-reg not valid");
       // This instruction is reading and writing X registers.  This may upset
       // the register scavenger and machine verifier, so we need to indicate
@@ -5121,6 +5114,51 @@ void AArch64InstrInfo::copyPhysReg(MachineBasicBlock &MBB,
     return;
   }
 
+  // GPR32 zeroing
+  if (AArch64::GPR32spRegClass.contains(DestReg) && SrcReg == AArch64::WZR) {
+    if (Subtarget.hasZeroCycleZeroingGPR32()) {
+      BuildMI(MBB, I, DL, get(AArch64::MOVZWi), DestReg)
+          .addImm(0)
+          .addImm(AArch64_AM::getShifterImm(AArch64_AM::LSL, 0));
+    } else {
+      BuildMI(MBB, I, DL, get(AArch64::ORRWrr), DestReg)
+          .addReg(AArch64::WZR)
+          .addReg(AArch64::WZR);
+    }
+    return;
+  }
+
+  if (AArch64::GPR64spRegClass.contains(DestReg) &&
+      AArch64::GPR64spRegClass.contains(SrcReg)) {
+    if (DestReg == AArch64::SP || SrcReg == AArch64::SP) {
+      // If either operand is SP, expand to ADD #0.
+      BuildMI(MBB, I, DL, get(AArch64::ADDXri), DestReg)
+          .addReg(SrcReg, getKillRegState(KillSrc))
+          .addImm(0)
+          .addImm(AArch64_AM::getShifterImm(AArch64_AM::LSL, 0));
+    } else {
+      // Otherwise, expand to ORR XZR.
+      BuildMI(MBB, I, DL, get(AArch64::ORRXrr), DestReg)
+          .addReg(AArch64::XZR)
+          .addReg(SrcReg, getKillRegState(KillSrc));
+    }
+    return;
+  }
+
+  // GPR64 zeroing
+  if (AArch64::GPR64spRegClass.contains(DestReg) && SrcReg == AArch64::XZR) {
+    if (Subtarget.hasZeroCycleZeroingGPR64()) {
+      BuildMI(MBB, I, DL, get(AArch64::MOVZXi), DestReg)
+          .addImm(0)
+          .addImm(AArch64_AM::getShifterImm(AArch64_AM::LSL, 0));
+    } else {
+      BuildMI(MBB, I, DL, get(AArch64::ORRXrr), DestReg)
+          .addReg(AArch64::XZR)
+          .addReg(AArch64::XZR);
+    }
+    return;
+  }
+
   // Copy a Predicate register by ORRing with itself.
   if (AArch64::PPRRegClass.contains(DestReg) &&
       AArch64::PPRRegClass.contains(SrcReg)) {
@@ -5205,27 +5243,6 @@ void AArch64InstrInfo::copyPhysReg(MachineBasicBlock &MBB,
     return;
   }
 
-  if (AArch64::GPR64spRegClass.contains(DestReg) &&
-      (AArch64::GPR64spRegClass.contains(SrcReg) || SrcReg == AArch64::XZR)) {
-    if (DestReg == AArch64::SP || SrcReg == AArch64::SP) {
-      // If either operand is SP, expand to ADD #0.
-      BuildMI(MBB, I, DL, get(AArch64::ADDXri), DestReg)
-          .addReg(SrcReg, getKillRegState(KillSrc))
-          .addImm(0)
-          .addImm(AArch64_AM::getShifterImm(AArch64_AM::LSL, 0));
-    } else if (SrcReg == AArch64::XZR && Subtarget.hasZeroCycleZeroingGPR64()) {
-      BuildMI(MBB, I, DL, get(AArch64::MOVZXi), DestReg)
-          .addImm(0)
-          .addImm(AArch64_AM::getShifterImm(AArch64_AM::LSL, 0));
-    } else {
-      // Otherwise, expand to ORR XZR.
-      BuildMI(MBB, I, DL, get(AArch64::ORRXrr), DestReg)
-          .addReg(AArch64::XZR)
-          .addReg(SrcReg, getKillRegState(KillSrc));
-    }
-    return;
-  }
-
   // Copy a DDDD register quad by copying the individual sub-registers.
   if (AArch64::DDDDRegClass.contains(DestReg) &&
       AArch64::DDDDRegClass.contains(SrcReg)) {

llvm/test/CodeGen/AArch64/arm64-copy-phys-zero-reg.mir

@@ -39,7 +39,7 @@ body:             |
     ; CHECK-NO-ZCM-GPR32-ZCM-GPR64-NO-ZCZ-LABEL: name: f0
     ; CHECK-NO-ZCM-GPR32-ZCM-GPR64-NO-ZCZ: liveins: $x0, $lr
     ; CHECK-NO-ZCM-GPR32-ZCM-GPR64-NO-ZCZ-NEXT: {{  $}}
-    ; CHECK-NO-ZCM-GPR32-ZCM-GPR64-NO-ZCZ-NEXT: $x0 = ORRXrr $xzr, undef $xzr, implicit $wzr
+    ; CHECK-NO-ZCM-GPR32-ZCM-GPR64-NO-ZCZ-NEXT: $w0 = ORRWrr $wzr, $wzr
     ; CHECK-NO-ZCM-GPR32-ZCM-GPR64-NO-ZCZ-NEXT: BL @f2, csr_darwin_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit $w0, implicit-def $sp, implicit-def $w0
     ;
     ; CHECK-ZCM-GPR32-ZCM-GPR64-NO-ZCZ-LABEL: name: f0
@@ -103,7 +103,7 @@ body:             |
     ; CHECK-ZCM-ZCZ: liveins: $x0, $lr
     ; CHECK-ZCM-ZCZ-NEXT: {{  $}}
     ; CHECK-ZCM-ZCZ-NEXT: $x0 = MOVZXi 0, 0
-    ; CHECK-ZCM-ZCZ-NEXT:BL @f2, csr_darwin_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit $w0, implicit-def $sp, implicit-def $w0
+    ; CHECK-ZCM-ZCZ-NEXT: BL @f2, csr_darwin_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit $w0, implicit-def $sp, implicit-def $w0
     $x0 = COPY $xzr
     BL @f2, csr_darwin_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit $w0, implicit-def $sp, implicit-def $w0
 ...