[llvm] 58e1c0e - [RISCV] Discard the false operand in vmerge.vvm -> vmv.v.v peephole (#106688)

[via llvm-commits]

Author: Luke Lau
Date: 2024-08-31T13:20:53+08:00
New Revision: 58e1c0e416f4a071482d1d9c2d620c7a0df4cf33

URL: https://github.com/llvm/llvm-project/commit/58e1c0e416f4a071482d1d9c2d620c7a0df4cf33
DIFF: https://github.com/llvm/llvm-project/commit/58e1c0e416f4a071482d1d9c2d620c7a0df4cf33.diff

LOG: [RISCV] Discard the false operand in vmerge.vvm -> vmv.v.v peephole (#106688)

vmerge.vvm needs to have an all ones mask, so nothing is taken from the
false operand. So instead of checking that the passthru is the same as
false, just use the passthru directly for the tail elements.

This supersedes the convertVMergeToVMv part of #105788, as noted in
https://github.com/llvm/llvm-project/pull/105788/files#r1731683971

Added: 
    

Modified: 
    llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp
    llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-to-vmv.mir

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp b/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp
index 6df3b951f5a06f..412fd790061a37 100644
--- a/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp
+++ b/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp
@@ -333,8 +333,8 @@ bool RISCVVectorPeephole::convertToWholeRegister(MachineInstr &MI) const {
   return true;
 }
 
-// Transform (VMERGE_VVM_<LMUL> false, false, true, allones, vl, sew) to
-// (VMV_V_V_<LMUL> false, true, vl, sew). It may decrease uses of VMSET.
+// Transform (VMERGE_VVM_<LMUL> pt, false, true, allones, vl, sew) to
+// (VMV_V_V_<LMUL> pt, true, vl, sew). It may decrease uses of VMSET.
 bool RISCVVectorPeephole::convertVMergeToVMv(MachineInstr &MI) const {
 #define CASE_VMERGE_TO_VMV(lmul)                                               \
   case RISCV::PseudoVMERGE_VVM_##lmul:                                         \
@@ -353,21 +353,12 @@ bool RISCVVectorPeephole::convertVMergeToVMv(MachineInstr &MI) const {
     CASE_VMERGE_TO_VMV(M8)
   }
 
-  Register PassthruReg = MI.getOperand(1).getReg();
-  Register FalseReg = MI.getOperand(2).getReg();
-  // Check passthru == false (or passthru == undef)
-  if (PassthruReg != RISCV::NoRegister &&
-      TRI->lookThruCopyLike(PassthruReg, MRI) !=
-          TRI->lookThruCopyLike(FalseReg, MRI))
-    return false;
-
   assert(MI.getOperand(4).isReg() && MI.getOperand(4).getReg() == RISCV::V0);
   if (!isAllOnesMask(V0Defs.lookup(&MI)))
     return false;
 
   MI.setDesc(TII->get(NewOpc));
-  MI.removeOperand(1);  // Passthru operand
-  MI.tieOperands(0, 1); // Tie false to dest
+  MI.removeOperand(2);  // False operand
   MI.removeOperand(3);  // Mask operand
   MI.addOperand(
       MachineOperand::CreateImm(RISCVII::TAIL_UNDISTURBED_MASK_UNDISTURBED));
@@ -375,7 +366,8 @@ bool RISCVVectorPeephole::convertVMergeToVMv(MachineInstr &MI) const {
   // vmv.v.v doesn't have a mask operand, so we may be able to inflate the
   // register class for the destination and passthru operands e.g. VRNoV0 -> VR
   MRI->recomputeRegClass(MI.getOperand(0).getReg());
-  MRI->recomputeRegClass(MI.getOperand(1).getReg());
+  if (MI.getOperand(1).getReg() != RISCV::NoRegister)
+    MRI->recomputeRegClass(MI.getOperand(1).getReg());
   return true;
 }
 

diff  --git a/llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-to-vmv.mir b/llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-to-vmv.mir
index 01fff3de0aa8bd..1419eede6ca9d1 100644
--- a/llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-to-vmv.mir
+++ b/llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-to-vmv.mir
@@ -15,7 +15,7 @@ body: |
     ; CHECK-NEXT: %avl:gprnox0 = COPY $x1
     ; CHECK-NEXT: %mask:vmv0 = PseudoVMSET_M_B8 %avl, 5 /* e32 */
     ; CHECK-NEXT: $v0 = COPY %mask
-    ; CHECK-NEXT: %x:vr = PseudoVMV_V_V_M1 %false, %true, %avl, 5 /* e32 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %x:vr = PseudoVMV_V_V_M1 $noreg, %true, %avl, 5 /* e32 */, 0 /* tu, mu */
     %false:vr = COPY $v8
     %true:vr = COPY $v9
     %avl:gprnox0 = COPY $x1
@@ -31,13 +31,13 @@ body: |
     ; CHECK-LABEL: name: undef_false
     ; CHECK: liveins: $x1, $v8, $v9
     ; CHECK-NEXT: {{  $}}
-    ; CHECK-NEXT: %pt:vrnov0 = COPY $v8
+    ; CHECK-NEXT: %pt:vr = COPY $v8
     ; CHECK-NEXT: %false:vr = COPY $noreg
     ; CHECK-NEXT: %true:vr = COPY $v9
     ; CHECK-NEXT: %avl:gprnox0 = COPY $x1
     ; CHECK-NEXT: %mask:vmv0 = PseudoVMSET_M_B8 %avl, 5 /* e32 */
     ; CHECK-NEXT: $v0 = COPY %mask
-    ; CHECK-NEXT: %x:vrnov0 = PseudoVMERGE_VVM_M1 %pt, %false, %true, $v0, %avl, 5 /* e32 */
+    ; CHECK-NEXT: %x:vr = PseudoVMV_V_V_M1 %pt, %true, %avl, 5 /* e32 */, 0 /* tu, mu */
     %pt:vrnov0 = COPY $v8
     %false:vr = COPY $noreg
     %true:vr = COPY $v9
@@ -55,12 +55,12 @@ body: |
     ; CHECK: liveins: $x1, $v8, $v9
     ; CHECK-NEXT: {{  $}}
     ; CHECK-NEXT: %false:vr = COPY $v8
-    ; CHECK-NEXT: %pt:vrnov0 = COPY $v8
+    ; CHECK-NEXT: %pt:vr = COPY $v8
     ; CHECK-NEXT: %true:vr = COPY $v9
     ; CHECK-NEXT: %avl:gprnox0 = COPY $x1
     ; CHECK-NEXT: %mask:vmv0 = PseudoVMSET_M_B8 %avl, 5 /* e32 */
     ; CHECK-NEXT: $v0 = COPY %mask
-    ; CHECK-NEXT: %x:vr = PseudoVMV_V_V_M1 %false, %true, %avl, 5 /* e32 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %x:vr = PseudoVMV_V_V_M1 %pt, %true, %avl, 5 /* e32 */, 0 /* tu, mu */
     %false:vr = COPY $v8
     %pt:vrnov0 = COPY $v8
     %true:vr = COPY $v9