[AArch64] Remove redundant ORRWrs which is generated by zero-extend

%3:gpr32 = ORRWrs $wzr, %2, 0
%4:gpr64 = SUBREG_TO_REG 0, %3, %subreg.sub_32

If AArch64's 32-bit form of instruction defines the source operand of ORRWrs,
we can remove the ORRWrs because the upper 32 bits of the source operand are
set to zero.

Differential Revision: https://reviews.llvm.org/D110841

llvm/lib/Target/AArch64/AArch64MIPeepholeOpt.cpp

@@ -15,6 +15,16 @@
 //    later. In this case, we could try to split the constant  operand of mov
 //    instruction into two bitmask immediates. It makes two AND instructions
 //    intead of multiple `mov` + `and` instructions.
+//
+// 2. Remove redundant ORRWrs which is generated by zero-extend.
+//
+//    %3:gpr32 = ORRWrs $wzr, %2, 0
+//    %4:gpr64 = SUBREG_TO_REG 0, %3, %subreg.sub_32
+//
+//    If AArch64's 32-bit form of instruction defines the source operand of
+//    ORRWrs, we can remove the ORRWrs because the upper 32 bits of the source
+//    operand are set to zero.
+//
 //===----------------------------------------------------------------------===//
 
 #include "AArch64ExpandImm.h"
@@ -44,6 +54,8 @@ struct AArch64MIPeepholeOpt : public MachineFunctionPass {
   template <typename T>
   bool visitAND(MachineInstr &MI,
                 SmallSetVector<MachineInstr *, 8> &ToBeRemoved);
+  bool visitORR(MachineInstr &MI,
+                SmallSetVector<MachineInstr *, 8> &ToBeRemoved);
   bool runOnMachineFunction(MachineFunction &MF) override;
 
   StringRef getPassName() const override {
@@ -196,6 +208,49 @@ bool AArch64MIPeepholeOpt::visitAND(
   return true;
 }
 
+bool AArch64MIPeepholeOpt::visitORR(
+    MachineInstr &MI, SmallSetVector<MachineInstr *, 8> &ToBeRemoved) {
+  // Check this ORR comes from below zero-extend pattern.
+  //
+  // def : Pat<(i64 (zext GPR32:$src)),
+  //           (SUBREG_TO_REG (i32 0), (ORRWrs WZR, GPR32:$src, 0), sub_32)>;
+  if (MI.getOperand(3).getImm() != 0)
+    return false;
+
+  if (MI.getOperand(1).getReg() != AArch64::WZR)
+    return false;
+
+  MachineInstr *SrcMI = MRI->getUniqueVRegDef(MI.getOperand(2).getReg());
+  if (!SrcMI)
+    return false;
+
+  // From https://developer.arm.com/documentation/dui0801/b/BABBGCAC
+  //
+  // When you use the 32-bit form of an instruction, the upper 32 bits of the
+  // source registers are ignored and the upper 32 bits of the destination
+  // register are set to zero.
+  //
+  // If AArch64's 32-bit form of instruction defines the source operand of
+  // zero-extend, we do not need the zero-extend. Let's check the MI's opcode is
+  // real AArch64 instruction and if it is not, do not process the opcode
+  // conservatively.
+  if (SrcMI->getOpcode() <= TargetOpcode::GENERIC_OP_END)
+    return false;
+
+  Register DefReg = MI.getOperand(0).getReg();
+  Register SrcReg = MI.getOperand(2).getReg();
+  MRI->replaceRegWith(DefReg, SrcReg);
+  MRI->clearKillFlags(SrcReg);
+  // replaceRegWith changes MI's definition register. Keep it for SSA form until
+  // deleting MI.
+  MI.getOperand(0).setReg(DefReg);
+  ToBeRemoved.insert(&MI);
+
+  LLVM_DEBUG({ dbgs() << "Removed: " << MI << "\n"; });
+
+  return true;
+}
+
 bool AArch64MIPeepholeOpt::runOnMachineFunction(MachineFunction &MF) {
   if (skipFunction(MF.getFunction()))
     return false;
@@ -221,6 +276,8 @@ bool AArch64MIPeepholeOpt::runOnMachineFunction(MachineFunction &MF) {
       case AArch64::ANDXrr:
         Changed = visitAND<uint64_t>(MI, ToBeRemoved);
         break;
+      case AArch64::ORRWrs:
+        Changed = visitORR(MI, ToBeRemoved);
       }
     }
   }

llvm/test/CodeGen/AArch64/arm64-assert-zext-sext.ll

@@ -1,9 +1,32 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: llc -O2 -mtriple=aarch64-linux-gnu < %s | FileCheck %s
 
 declare i32 @test(i32) local_unnamed_addr
 declare i32 @test1(i64) local_unnamed_addr
 
 define i32 @assertzext(i32 %n, i1 %a, i32* %b) local_unnamed_addr {
+; CHECK-LABEL: assertzext:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    stp x30, x19, [sp, #-16]! // 16-byte Folded Spill
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    .cfi_offset w19, -8
+; CHECK-NEXT:    .cfi_offset w30, -16
+; CHECK-NEXT:    mov w8, #33066
+; CHECK-NEXT:    tst w1, #0x1
+; CHECK-NEXT:    movk w8, #28567, lsl #16
+; CHECK-NEXT:    csel w19, wzr, w8, ne
+; CHECK-NEXT:    cbnz w0, .LBB0_2
+; CHECK-NEXT:  // %bb.1: // %if.then
+; CHECK-NEXT:    mov w19, wzr
+; CHECK-NEXT:    str wzr, [x2]
+; CHECK-NEXT:  .LBB0_2: // %if.end
+; CHECK-NEXT:    mov w0, w19
+; CHECK-NEXT:    bl test
+; CHECK-NEXT:    mov w0, w19
+; CHECK-NEXT:    bl test1
+; CHECK-NEXT:    mov w0, wzr
+; CHECK-NEXT:    ldp x30, x19, [sp], #16 // 16-byte Folded Reload
+; CHECK-NEXT:    ret
 entry:
   %i = select i1 %a, i64 0, i64 66296709418
   %conv.i = trunc i64 %i to i32
@@ -20,14 +43,29 @@ if.end:                      ; preds = %if.then, %entry
   %i2 = sext i32 %i1 to i64
   %call1.i = tail call i32 @test1(i64 %i2)
   ret i32 0
-; CHECK:       // %if.end
-; CHECK:       mov     w{{[0-9]+}}, w{{[0-9]+}}
-; CHECK:       bl      test
-; CHECK:       mov     w{{[0-9]+}}, w{{[0-9]+}}
-; CHECK:       bl      test1
 }
 
 define i32 @assertsext(i32 %n, i8 %a) local_unnamed_addr {
+; CHECK-LABEL: assertsext:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    cbz w0, .LBB1_2
+; CHECK-NEXT:  // %bb.1:
+; CHECK-NEXT:    mov x0, xzr
+; CHECK-NEXT:    b .LBB1_3
+; CHECK-NEXT:  .LBB1_2: // %if.then
+; CHECK-NEXT:    mov x9, #24575
+; CHECK-NEXT:    sxtb w8, w1
+; CHECK-NEXT:    movk x9, #15873, lsl #16
+; CHECK-NEXT:    movk x9, #474, lsl #32
+; CHECK-NEXT:    udiv x0, x9, x8
+; CHECK-NEXT:  .LBB1_3: // %if.end
+; CHECK-NEXT:    str x30, [sp, #-16]! // 8-byte Folded Spill
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    .cfi_offset w30, -16
+; CHECK-NEXT:    bl test1
+; CHECK-NEXT:    mov w0, wzr
+; CHECK-NEXT:    ldr x30, [sp], #16 // 8-byte Folded Reload
+; CHECK-NEXT:    ret
 entry:
   %conv.i = sext i8 %a to i32
   %cmp = icmp eq i32 %n, 0
@@ -37,9 +75,6 @@ if.then:                     ; preds = %entry
   %conv1 = zext i32 %conv.i to i64
   %div = udiv i64 2036854775807, %conv1
   br label %if.end
-; CHECK:       // %if.then
-; CHECK:       mov     w{{[0-9]+}}, w{{[0-9]+}}
-; CHECK:       udiv    x{{[0-9]+}}, x{{[0-9]+}}, x{{[0-9]+}}
 
 if.end:                      ; preds = %if.then, %entry
   %i1 = phi i64 [ %div, %if.then ], [ 0, %entry ]

llvm/test/CodeGen/AArch64/redundant-mov-from-zero-extend.ll

@@ -0,0 +1,79 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -O3 -mtriple=aarch64-linux-gnu < %s | FileCheck %s
+
+define i32 @test(i32 %input, i32 %n, i32 %a) {
+; CHECK-LABEL: test:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    cbz w1, .LBB0_2
+; CHECK-NEXT:  // %bb.1:
+; CHECK-NEXT:    mov w0, wzr
+; CHECK-NEXT:    ret
+; CHECK-NEXT:  .LBB0_2: // %bb.0
+; CHECK-NEXT:    add w8, w0, w1
+; CHECK-NEXT:    mov w0, #100
+; CHECK-NEXT:    cmp w8, #4
+; CHECK-NEXT:    b.hi .LBB0_5
+; CHECK-NEXT:  // %bb.3: // %bb.0
+; CHECK-NEXT:    adrp x9, .LJTI0_0
+; CHECK-NEXT:    add x9, x9, :lo12:.LJTI0_0
+; CHECK-NEXT:    adr x10, .LBB0_4
+; CHECK-NEXT:    ldrb w11, [x9, x8]
+; CHECK-NEXT:    add x10, x10, x11, lsl #2
+; CHECK-NEXT:    br x10
+; CHECK-NEXT:  .LBB0_4: // %sw.bb
+; CHECK-NEXT:    add w0, w2, #1
+; CHECK-NEXT:    ret
+; CHECK-NEXT:  .LBB0_5: // %bb.0
+; CHECK-NEXT:    cmp w8, #200
+; CHECK-NEXT:    b.ne .LBB0_10
+; CHECK-NEXT:  // %bb.6: // %sw.bb7
+; CHECK-NEXT:    add w0, w2, #7
+; CHECK-NEXT:    ret
+; CHECK-NEXT:  .LBB0_7: // %sw.bb1
+; CHECK-NEXT:    add w0, w2, #3
+; CHECK-NEXT:    ret
+; CHECK-NEXT:  .LBB0_8: // %sw.bb3
+; CHECK-NEXT:    add w0, w2, #4
+; CHECK-NEXT:    ret
+; CHECK-NEXT:  .LBB0_9: // %sw.bb5
+; CHECK-NEXT:    add w0, w2, #5
+; CHECK-NEXT:  .LBB0_10: // %return
+; CHECK-NEXT:    ret
+entry:
+  %b = add nsw i32 %input, %n
+  %cmp = icmp eq i32 %n, 0
+  br i1 %cmp, label %bb.0, label %return
+
+bb.0:
+  switch i32 %b, label %return [
+    i32 0, label %sw.bb
+    i32 1, label %sw.bb1
+    i32 2, label %sw.bb3
+    i32 4, label %sw.bb5
+    i32 200, label %sw.bb7
+  ]
+
+sw.bb:
+  %add = add nsw i32 %a, 1
+  br label %return
+
+sw.bb1:
+  %add2 = add nsw i32 %a, 3
+  br label %return
+
+sw.bb3:
+  %add4 = add nsw i32 %a, 4
+  br label %return
+
+sw.bb5:
+  %add6 = add nsw i32 %a, 5
+  br label %return
+
+sw.bb7:
+  %add8 = add nsw i32 %a, 7
+  br label %return
+
+return:
+  %retval.0 = phi i32 [ %add8, %sw.bb7 ], [ %add6, %sw.bb5 ], [ %add4, %sw.bb3 ], [ %add2, %sw.bb1 ], [ %add, %sw.bb ], [ 100, %bb.0 ], [ 0, %entry ]
+  ret i32 %retval.0
+}

llvm/test/CodeGen/AArch64/redundant-orrwrs-from-zero-extend.mir

@@ -0,0 +1,69 @@
+# RUN: llc -mtriple=aarch64 -run-pass aarch64-mi-peephole-opt -verify-machineinstrs -o - %s | FileCheck %s
+---
+name:            test1
+# CHECK-LABEL: name: test1
+alignment:       4
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: gpr32 }
+  - { id: 1, class: gpr32 }
+  - { id: 2, class: gpr32 }
+  - { id: 3, class: gpr32 }
+  - { id: 4, class: gpr64 }
+body:             |
+  bb.0:
+    liveins: $w0, $w1
+
+    %0:gpr32 = COPY $w0
+    %1:gpr32 = COPY $w1
+    B %bb.1
+
+  bb.1:
+    %2:gpr32 = nsw ADDWrr %0, %1
+    B %bb.2
+
+  bb.2:
+    ; CHECK-LABEL: bb.2:
+    ; CHECK-NOT: %3:gpr32 = ORRWrs $wzr, %2, 0
+    ; The ORRWrs should be removed.
+    %3:gpr32 = ORRWrs $wzr, %2, 0
+    %4:gpr64 = SUBREG_TO_REG 0, %3, %subreg.sub_32
+    B %bb.3
+
+  bb.3:
+    $x0 = COPY %4
+    RET_ReallyLR implicit $x0
+...
+---
+name:            test2
+# CHECK-LABEL: name: test2
+alignment:       4
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: gpr64 }
+  - { id: 1, class: gpr32 }
+  - { id: 2, class: gpr32 }
+  - { id: 3, class: gpr64 }
+body:             |
+  bb.0:
+    liveins: $x0
+
+    %0:gpr64 = COPY $x0
+    B %bb.1
+
+  bb.1:
+    %1:gpr32 = EXTRACT_SUBREG %0, %subreg.sub_32
+    B %bb.2
+
+  bb.2:
+    ; CHECK-LABEL: bb.2:
+    ; CHECK: %2:gpr32 = ORRWrs $wzr, %1, 0
+    ; The ORRWrs should not be removed.
+    %2:gpr32 = ORRWrs $wzr, %1, 0
+    %3:gpr64 = SUBREG_TO_REG 0, %2, %subreg.sub_32
+    B %bb.3
+
+  bb.3:
+    $x0 = COPY %3
+    RET_ReallyLR implicit $x0
+...