[RISCV] Support postRA vsetvl insertion pass (#70549)

This patch try to get rid of vsetvl implict vl/vtype def-use chain and
improve the register allocation quality by moving the vsetvl insertion
pass after RVV register allocation

It will gain the benefit for the following optimization from

1. unblock scheduler's constraints by removing vl/vtype def-use chain
2. Support RVV re-materialization
3. Support partial spill

This patch add a new option `-riscv-vsetvl-after-rvv-regalloc=<1|0>` to
control this feature and default set as disable.

llvm/lib/Target/RISCV/RISCVTargetMachine.cpp

@@ -96,6 +96,11 @@ static cl::opt<bool> EnableMISchedLoadClustering(
     cl::desc("Enable load clustering in the machine scheduler"),
     cl::init(false));
 
+static cl::opt<bool> EnableVSETVLIAfterRVVRegAlloc(
+    "riscv-vsetvl-after-rvv-regalloc", cl::Hidden,
+    cl::desc("Insert vsetvls after vector register allocation"),
+    cl::init(true));
+
 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeRISCVTarget() {
   RegisterTargetMachine<RISCVTargetMachine> X(getTheRISCV32Target());
   RegisterTargetMachine<RISCVTargetMachine> Y(getTheRISCV64Target());
@@ -389,6 +394,8 @@ FunctionPass *RISCVPassConfig::createRVVRegAllocPass(bool Optimized) {
 
 bool RISCVPassConfig::addRegAssignAndRewriteFast() {
   addPass(createRVVRegAllocPass(false));
+  if (EnableVSETVLIAfterRVVRegAlloc)
+    addPass(createRISCVInsertVSETVLIPass());
   addPass(createRISCVCoalesceVSETVLIPass());
   if (TM->getOptLevel() != CodeGenOptLevel::None &&
       EnableRISCVDeadRegisterElimination)
@@ -399,6 +406,8 @@ bool RISCVPassConfig::addRegAssignAndRewriteFast() {
 bool RISCVPassConfig::addRegAssignAndRewriteOptimized() {
   addPass(createRVVRegAllocPass(true));
   addPass(createVirtRegRewriter(false));
+  if (EnableVSETVLIAfterRVVRegAlloc)
+    addPass(createRISCVInsertVSETVLIPass());
   addPass(createRISCVCoalesceVSETVLIPass());
   if (TM->getOptLevel() != CodeGenOptLevel::None &&
       EnableRISCVDeadRegisterElimination)
@@ -547,10 +556,12 @@ void RISCVPassConfig::addPreRegAlloc() {
 
   // Run RISCVInsertVSETVLI after PHI elimination. On O1 and above do it after
   // register coalescing so needVSETVLIPHI doesn't need to look through COPYs.
-  if (TM->getOptLevel() == CodeGenOptLevel::None)
-    insertPass(&PHIEliminationID, &RISCVInsertVSETVLIID);
-  else
-    insertPass(&RegisterCoalescerID, &RISCVInsertVSETVLIID);
+  if (!EnableVSETVLIAfterRVVRegAlloc) {
+    if (TM->getOptLevel() == CodeGenOptLevel::None)
+      insertPass(&PHIEliminationID, &RISCVInsertVSETVLIID);
+    else
+      insertPass(&RegisterCoalescerID, &RISCVInsertVSETVLIID);
+  }
 }
 
 void RISCVPassConfig::addFastRegAlloc() {

llvm/test/CodeGen/RISCV/O0-pipeline.ll

@@ -44,14 +44,12 @@
 ; CHECK-NEXT:       RISC-V Insert Write VXRM Pass
 ; CHECK-NEXT:       Init Undef Pass
 ; CHECK-NEXT:       Eliminate PHI nodes for register allocation
-; CHECK-NEXT:       MachineDominator Tree Construction
-; CHECK-NEXT:       Slot index numbering
-; CHECK-NEXT:       Live Interval Analysis
-; CHECK-NEXT:       RISC-V Insert VSETVLI pass
 ; CHECK-NEXT:       Two-Address instruction pass
 ; CHECK-NEXT:       Fast Register Allocator
+; CHECK-NEXT:       MachineDominator Tree Construction
 ; CHECK-NEXT:       Slot index numbering
 ; CHECK-NEXT:       Live Interval Analysis
+; CHECK-NEXT:       RISC-V Insert VSETVLI pass
 ; CHECK-NEXT:       RISC-V Coalesce VSETVLI pass
 ; CHECK-NEXT:       Fast Register Allocator
 ; CHECK-NEXT:       Remove Redundant DEBUG_VALUE analysis

llvm/test/CodeGen/RISCV/O3-pipeline.ll

@@ -128,7 +128,6 @@
 ; CHECK-NEXT:       Slot index numbering
 ; CHECK-NEXT:       Live Interval Analysis
 ; CHECK-NEXT:       Register Coalescer
-; CHECK-NEXT:       RISC-V Insert VSETVLI pass
 ; CHECK-NEXT:       Rename Disconnected Subregister Components
 ; CHECK-NEXT:       Machine Instruction Scheduler
 ; CHECK-NEXT:       Machine Block Frequency Analysis
@@ -142,6 +141,7 @@
 ; CHECK-NEXT:       Machine Optimization Remark Emitter
 ; CHECK-NEXT:       Greedy Register Allocator
 ; CHECK-NEXT:       Virtual Register Rewriter
+; CHECK-NEXT:       RISC-V Insert VSETVLI pass
 ; CHECK-NEXT:       RISC-V Coalesce VSETVLI pass
 ; CHECK-NEXT:       RISC-V Dead register definitions
 ; CHECK-NEXT:       Virtual Register Map

llvm/test/CodeGen/RISCV/early-clobber-tied-def-subreg-liveness.ll

@@ -24,36 +24,36 @@ define void @_Z3foov() {
 ; CHECK-NEXT:    lui a0, %hi(.L__const._Z3foov.var_49)
 ; CHECK-NEXT:    addi a0, a0, %lo(.L__const._Z3foov.var_49)
 ; CHECK-NEXT:    vsetivli zero, 2, e16, m2, ta, ma
-; CHECK-NEXT:    vle16.v v8, (a0)
+; CHECK-NEXT:    vle16.v v10, (a0)
 ; CHECK-NEXT:    lui a0, %hi(.L__const._Z3foov.var_48)
 ; CHECK-NEXT:    addi a0, a0, %lo(.L__const._Z3foov.var_48)
-; CHECK-NEXT:    vle8.v v10, (a0)
+; CHECK-NEXT:    vle8.v v8, (a0)
 ; CHECK-NEXT:    csrr a0, vlenb
 ; CHECK-NEXT:    slli a0, a0, 3
 ; CHECK-NEXT:    add a0, sp, a0
 ; CHECK-NEXT:    addi a0, a0, 16
-; CHECK-NEXT:    vs1r.v v10, (a0) # Unknown-size Folded Spill
+; CHECK-NEXT:    vs1r.v v8, (a0) # Unknown-size Folded Spill
 ; CHECK-NEXT:    lui a0, %hi(.L__const._Z3foov.var_46)
 ; CHECK-NEXT:    addi a0, a0, %lo(.L__const._Z3foov.var_46)
-; CHECK-NEXT:    vle16.v v10, (a0)
+; CHECK-NEXT:    vle16.v v12, (a0)
 ; CHECK-NEXT:    lui a0, %hi(.L__const._Z3foov.var_45)
 ; CHECK-NEXT:    addi a0, a0, %lo(.L__const._Z3foov.var_45)
-; CHECK-NEXT:    vle16.v v12, (a0)
+; CHECK-NEXT:    vle16.v v14, (a0)
 ; CHECK-NEXT:    addi a0, sp, 16
 ; CHECK-NEXT:    csrr a1, vlenb
 ; CHECK-NEXT:    slli a1, a1, 1
-; CHECK-NEXT:    vs2r.v v8, (a0) # Unknown-size Folded Spill
-; CHECK-NEXT:    add a0, a0, a1
 ; CHECK-NEXT:    vs2r.v v10, (a0) # Unknown-size Folded Spill
 ; CHECK-NEXT:    add a0, a0, a1
 ; CHECK-NEXT:    vs2r.v v12, (a0) # Unknown-size Folded Spill
 ; CHECK-NEXT:    add a0, a0, a1
 ; CHECK-NEXT:    vs2r.v v14, (a0) # Unknown-size Folded Spill
+; CHECK-NEXT:    add a0, a0, a1
+; CHECK-NEXT:    vs2r.v v16, (a0) # Unknown-size Folded Spill
 ; CHECK-NEXT:    #APP
 ; CHECK-NEXT:    #NO_APP
-; CHECK-NEXT:    vsetivli zero, 2, e16, m2, ta, ma
 ; CHECK-NEXT:    lui a0, %hi(.L__const._Z3foov.var_40)
 ; CHECK-NEXT:    addi a0, a0, %lo(.L__const._Z3foov.var_40)
+; CHECK-NEXT:    vsetivli zero, 2, e16, m2, ta, ma
 ; CHECK-NEXT:    vle16.v v8, (a0)
 ; CHECK-NEXT:    lui a0, %hi(.L__const._Z3foov.var_44)
 ; CHECK-NEXT:    addi a0, a0, %lo(.L__const._Z3foov.var_44)
@@ -71,12 +71,12 @@ define void @_Z3foov() {
 ; CHECK-NEXT:    lui a0, 1048572
 ; CHECK-NEXT:    addi a0, a0, 928
 ; CHECK-NEXT:    vmsbc.vx v0, v8, a0
-; CHECK-NEXT:    vsetvli zero, zero, e16, m2, tu, mu
 ; CHECK-NEXT:    csrr a0, vlenb
 ; CHECK-NEXT:    slli a0, a0, 3
 ; CHECK-NEXT:    add a0, sp, a0
 ; CHECK-NEXT:    addi a0, a0, 16
 ; CHECK-NEXT:    vl1r.v v8, (a0) # Unknown-size Folded Reload
+; CHECK-NEXT:    vsetvli zero, zero, e16, m2, tu, mu
 ; CHECK-NEXT:    vsext.vf2 v10, v8, v0.t
 ; CHECK-NEXT:    lui a0, %hi(var_47)
 ; CHECK-NEXT:    addi a0, a0, %lo(var_47)

llvm/test/CodeGen/RISCV/intrinsic-cttz-elts-vscale.ll

@@ -75,18 +75,18 @@ define i64 @ctz_nxv8i1_no_range(<vscale x 8 x i16> %a) {
 ; RV32-NEXT:    sw a0, 16(sp)
 ; RV32-NEXT:    addi a2, sp, 16
 ; RV32-NEXT:    vsetvli a3, zero, e64, m8, ta, ma
-; RV32-NEXT:    vlse64.v v16, (a2), zero
-; RV32-NEXT:    vid.v v8
+; RV32-NEXT:    vlse64.v v8, (a2), zero
+; RV32-NEXT:    vid.v v16
 ; RV32-NEXT:    li a2, -1
-; RV32-NEXT:    vmadd.vx v8, a2, v16
-; RV32-NEXT:    vsetvli zero, zero, e16, m2, ta, ma
+; RV32-NEXT:    vmadd.vx v16, a2, v8
 ; RV32-NEXT:    addi a2, sp, 32
-; RV32-NEXT:    vl2r.v v16, (a2) # Unknown-size Folded Reload
-; RV32-NEXT:    vmsne.vi v0, v16, 0
+; RV32-NEXT:    vl2r.v v8, (a2) # Unknown-size Folded Reload
+; RV32-NEXT:    vsetvli zero, zero, e16, m2, ta, ma
+; RV32-NEXT:    vmsne.vi v0, v8, 0
 ; RV32-NEXT:    vsetvli zero, zero, e64, m8, ta, ma
-; RV32-NEXT:    vmv.v.i v16, 0
-; RV32-NEXT:    vmerge.vim v16, v16, -1, v0
-; RV32-NEXT:    vand.vv v8, v8, v16
+; RV32-NEXT:    vmv.v.i v8, 0
+; RV32-NEXT:    vmerge.vim v8, v8, -1, v0
+; RV32-NEXT:    vand.vv v8, v16, v8
 ; RV32-NEXT:    vredmaxu.vs v8, v8, v8
 ; RV32-NEXT:    vmv.x.s a2, v8
 ; RV32-NEXT:    sltu a3, a0, a2
@@ -108,15 +108,15 @@ define i64 @ctz_nxv8i1_no_range(<vscale x 8 x i16> %a) {
 ; RV64:       # %bb.0:
 ; RV64-NEXT:    csrr a0, vlenb
 ; RV64-NEXT:    vsetvli a1, zero, e64, m8, ta, ma
-; RV64-NEXT:    vmv.v.x v24, a0
-; RV64-NEXT:    vid.v v16
+; RV64-NEXT:    vmv.v.x v16, a0
+; RV64-NEXT:    vid.v v24
 ; RV64-NEXT:    li a1, -1
-; RV64-NEXT:    vmadd.vx v16, a1, v24
+; RV64-NEXT:    vmadd.vx v24, a1, v16
 ; RV64-NEXT:    vsetvli zero, zero, e16, m2, ta, ma
 ; RV64-NEXT:    vmsne.vi v0, v8, 0
 ; RV64-NEXT:    vsetvli zero, zero, e64, m8, ta, ma
 ; RV64-NEXT:    vmv.v.i v8, 0
-; RV64-NEXT:    vmerge.vvm v8, v8, v16, v0
+; RV64-NEXT:    vmerge.vvm v8, v8, v24, v0
 ; RV64-NEXT:    vredmaxu.vs v8, v8, v8
 ; RV64-NEXT:    vmv.x.s a1, v8
 ; RV64-NEXT:    sub a0, a0, a1