[PATCH] D122769: [RISCV] Add a prepass to vsetvli insertion to propagate VLMAX vsetvli to the instructions.

[Craig Topper via Phabricator via llvm-commits]

craig.topper updated this revision to Diff 425057.
craig.topper added a comment.

Address feedback
Rebase on top of pre-committed test.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D122769/new/

https://reviews.llvm.org/D122769

Files:
  llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
  llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll


Index: llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll
===================================================================
--- llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll
+++ llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll
@@ -591,21 +591,20 @@
 ; CHECK-NEXT:    blez a0, .LBB11_3
 ; CHECK-NEXT:  # %bb.1: # %for.body.preheader
 ; CHECK-NEXT:    li a5, 0
-; CHECK-NEXT:    li t1, 0
+; CHECK-NEXT:    li t0, 0
 ; CHECK-NEXT:    slli a7, a6, 3
 ; CHECK-NEXT:  .LBB11_2: # %for.body
 ; CHECK-NEXT:    # =>This Inner Loop Header: Depth=1
-; CHECK-NEXT:    add t0, a2, a5
-; CHECK-NEXT:    vsetvli zero, a6, e64, m1, ta, mu
-; CHECK-NEXT:    vle64.v v8, (t0)
+; CHECK-NEXT:    add a4, a2, a5
+; CHECK-NEXT:    vle64.v v8, (a4)
 ; CHECK-NEXT:    add a4, a3, a5
 ; CHECK-NEXT:    vle64.v v9, (a4)
 ; CHECK-NEXT:    vfadd.vv v8, v8, v9
 ; CHECK-NEXT:    add a4, a1, a5
 ; CHECK-NEXT:    vse64.v v8, (a4)
-; CHECK-NEXT:    add t1, t1, a6
+; CHECK-NEXT:    add t0, t0, a6
 ; CHECK-NEXT:    add a5, a5, a7
-; CHECK-NEXT:    blt t1, a0, .LBB11_2
+; CHECK-NEXT:    blt t0, a0, .LBB11_2
 ; CHECK-NEXT:  .LBB11_3: # %for.end
 ; CHECK-NEXT:    ret
 entry:
Index: llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
+++ llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
@@ -435,6 +435,7 @@
   void insertVSETVLI(MachineBasicBlock &MBB, MachineInstr &MI,
                      const VSETVLIInfo &Info, const VSETVLIInfo &PrevInfo);
 
+  void forwardPropagateVLMAX(MachineBasicBlock &MBB);
   bool computeVLVTYPEChanges(const MachineBasicBlock &MBB);
   void computeIncomingVLVTYPE(const MachineBasicBlock &MBB);
   void emitVSETVLIs(MachineBasicBlock &MBB);
@@ -887,6 +888,44 @@
   return CurInfo.isCompatibleWithLoadStoreEEW(EEW, Require);
 }
 
+// Forward propagate VLMAX vsetvlis.
+void RISCVInsertVSETVLI::forwardPropagateVLMAX(MachineBasicBlock &MBB) {
+  for (const MachineInstr &MI : MBB) {
+    // Look for VLMAX vsetvlis.
+    if (!(isVectorConfigInstr(MI) && MI.getOperand(1).isReg() &&
+          MI.getOperand(1).getReg() == RISCV::X0 &&
+          MI.getOperand(0).getReg() != RISCV::X0))
+      continue;
+
+    const MachineOperand &DestVLOp = MI.getOperand(0);
+    Register DestVLReg = DestVLOp.getReg();
+    // Walk through all uses of this VL.
+    for (MachineRegisterInfo::use_nodbg_iterator
+             UI = MRI->use_nodbg_begin(DestVLReg),
+             UIEnd = MRI->use_nodbg_end();
+         UI != UIEnd;) {
+      MachineOperand &Use(*UI++);
+      assert(Use.getParent() != nullptr && "Expected parent instruction");
+      const MachineInstr &UseMI = *Use.getParent();
+      const unsigned UseIndex = UseMI.getOperandNo(&Use);
+
+      uint64_t TSFlags = UseMI.getDesc().TSFlags;
+      if (RISCVII::hasSEWOp(TSFlags) && RISCVII::hasVLOp(TSFlags)) {
+        unsigned NumOperands = UseMI.getNumExplicitOperands();
+        if (RISCVII::hasVecPolicyOp(TSFlags))
+          --NumOperands;
+
+        // NumOperands - 2 == VLOpIndex
+        if (UseIndex == (NumOperands - 2)) {
+          Use.setReg(RISCV::X0);
+          // TODO: Should we update the dead flag or remove the instruction if
+          // we propagated to all users?
+        }
+      }
+    }
+  }
+}
+
 bool RISCVInsertVSETVLI::computeVLVTYPEChanges(const MachineBasicBlock &MBB) {
   bool HadVectorOp = false;
 
@@ -1143,6 +1182,10 @@
   assert(BlockInfo.empty() && "Expect empty block infos");
   BlockInfo.resize(MF.getNumBlockIDs());
 
+  // Phase 0 - propagate VLMAX vsetvlis.
+  for (MachineBasicBlock &MBB : MF)
+    forwardPropagateVLMAX(MBB);
+
   bool HaveVectorOp = false;
 
   // Phase 1 - determine how VL/VTYPE are affected by the each block.


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