[RISCV] Don't forward AVL in VSETVLIInfo if it would clobber other definitions

llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp

@@ -956,6 +956,12 @@ void RISCVInsertVSETVLI::forwardVSETVLIAVL(VSETVLIInfo &Info) const {
   VSETVLIInfo DefInstrInfo = getInfoForVSETVLI(*DefMI);
   if (!DefInstrInfo.hasSameVLMAX(Info))
     return;
+  // If the AVL is a register with multiple definitions, don't forward it. We
+  // might not be able to extend its LiveInterval without clobbering other val
+  // nums.
+  if (DefInstrInfo.hasAVLReg() &&
+      !LIS->getInterval(DefInstrInfo.getAVLReg()).containsOneValue())
+    return;
   Info.setAVL(DefInstrInfo);
 }
 

llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll

@@ -1125,3 +1125,39 @@ exit:
   call void @llvm.riscv.vse.nxv8i8(<vscale x 8 x i8> %1, ptr %p, i64 1)
   ret void
 }
+
+; Check that we don't forward an AVL if we wouldn't be able to extend its
+; LiveInterval without clobbering other val nos.
+define <vscale x 4 x i32> @unforwardable_avl(i64 %n, <vscale x 4 x i32> %v, i1 %cmp) {
+; CHECK-LABEL: unforwardable_avl:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    vsetvli a2, a0, e32, m2, ta, ma
+; CHECK-NEXT:    andi a1, a1, 1
+; CHECK-NEXT:  .LBB27_1: # %for.body
+; CHECK-NEXT:    # =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    addi a0, a0, 1
+; CHECK-NEXT:    bnez a1, .LBB27_1
+; CHECK-NEXT:  # %bb.2: # %for.cond.cleanup
+; CHECK-NEXT:    vsetvli a0, zero, e32, m2, ta, ma
+; CHECK-NEXT:    vadd.vv v10, v8, v8
+; CHECK-NEXT:    vsetvli zero, a2, e32, m2, ta, ma
+; CHECK-NEXT:    vadd.vv v8, v10, v8
+; CHECK-NEXT:    ret
+entry:
+  %0 = tail call i64 @llvm.riscv.vsetvli.i64(i64 %n, i64 2, i64 1)
+  br label %for.body
+
+for.body:
+  ; Use %n in a PHI here so its virtual register is assigned to a second time here.
+  %1 = phi i64 [ %3, %for.body ], [ %n, %entry ]
+  %2 = tail call i64 @llvm.riscv.vsetvli.i64(i64 %1, i64 0, i64 0)
+  %3 = add i64 %1, 1
+  br i1 %cmp, label %for.body, label %for.cond.cleanup
+
+for.cond.cleanup:
+  %4 = tail call <vscale x 4 x i32> @llvm.riscv.vadd.nxv2f32.nxv2f32.i64(<vscale x 4 x i32> undef, <vscale x 4 x i32> %v, <vscale x 4 x i32> %v, i64 -1)
+  ; VL toggle needed here: If the %n AVL was forwarded here we wouldn't be able
+  ; to extend it's LiveInterval because it would clobber the assignment at %1.
+  %5 = tail call <vscale x 4 x i32> @llvm.riscv.vadd.nxv2f32.nxv2f32.i64(<vscale x 4 x i32> undef, <vscale x 4 x i32> %4, <vscale x 4 x i32> %v, i64 %0)
+  ret <vscale x 4 x i32> %5
+}

llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.mir

@@ -134,6 +134,10 @@
     ret void
   }
 
+  define void @unforwardable_avl() {
+    ret void
+  }
+
   declare i32 @llvm.vector.reduce.add.v4i32(<4 x i32>)
 
   declare <vscale x 1 x i64> @llvm.riscv.vadd.nxv1i64.nxv1i64.i64(<vscale x 1 x i64>, <vscale x 1 x i64>, <vscale x 1 x i64>, i64) #1
@@ -990,3 +994,43 @@ body: |
     %x:gpr = PseudoVMV_X_S undef $noreg, 6
     PseudoBR %bb.1
 ...
+---
+name: unforwardable_avl
+tracksRegLiveness: true
+body: |
+  ; CHECK-LABEL: name: unforwardable_avl
+  ; CHECK: bb.0:
+  ; CHECK-NEXT:   successors: %bb.1(0x80000000)
+  ; CHECK-NEXT:   liveins: $x10, $v8m2
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   %avl:gprnox0 = COPY $x10
+  ; CHECK-NEXT:   %outvl:gprnox0 = PseudoVSETVLI %avl, 209 /* e32, m2, ta, ma */, implicit-def $vl, implicit-def $vtype
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1:
+  ; CHECK-NEXT:   successors: %bb.2(0x80000000)
+  ; CHECK-NEXT:   liveins: $v8m2
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   dead %avl:gprnox0 = ADDI %avl, 1
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.2:
+  ; CHECK-NEXT:   liveins: $v8m2
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   dead [[PseudoVSETVLIX0_:%[0-9]+]]:gpr = PseudoVSETVLIX0 killed $x0, 209 /* e32, m2, ta, ma */, implicit-def $vl, implicit-def $vtype
+  ; CHECK-NEXT:   renamable $v10m2 = PseudoVADD_VV_M2 undef renamable $v10m2, renamable $v8m2, renamable $v8m2, -1, 5 /* e32 */, 0 /* tu, mu */, implicit $vl, implicit $vtype
+  ; CHECK-NEXT:   dead $x0 = PseudoVSETVLI %outvl, 209 /* e32, m2, ta, ma */, implicit-def $vl, implicit-def $vtype
+  ; CHECK-NEXT:   renamable $v8m2 = PseudoVADD_VV_M2 undef renamable $v8m2, killed renamable $v10m2, renamable $v8m2, $noreg, 5 /* e32 */, 0 /* tu, mu */, implicit $vl, implicit $vtype
+  ; CHECK-NEXT:   PseudoRET implicit $v8m2
+  bb.0:
+    liveins: $x10, $v8m2
+    %avl:gprnox0 = COPY $x10
+    %outvl:gprnox0 = PseudoVSETVLI %avl:gprnox0, 209, implicit-def dead $vl, implicit-def dead $vtype
+
+  bb.1:
+    liveins: $v8m2
+    %avl:gprnox0 = ADDI %avl:gprnox0, 1
+
+  bb.2:
+    liveins: $v8m2
+    renamable $v10m2 = PseudoVADD_VV_M2 undef renamable $v10m2, renamable $v8m2, renamable $v8m2, -1, 5, 0
+    renamable $v8m2 = PseudoVADD_VV_M2 undef renamable $v8m2, killed renamable $v10m2, killed renamable $v8m2, %outvl:gprnox0, 5, 0
+    PseudoRET implicit $v8m2

llvm/test/Transforms/LoopStrengthReduce/RISCV/lsr-drop-solution.ll

@@ -20,6 +20,7 @@ define ptr @foo(ptr %a0, ptr %a1, i64 %a2) {
 ; CHECK-NEXT:    mv a3, a0
 ; CHECK-NEXT:  .LBB0_3: # %do.body
 ; CHECK-NEXT:    # =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    vsetvli zero, a4, e8, m8, ta, ma
 ; CHECK-NEXT:    vle8.v v8, (a1)
 ; CHECK-NEXT:    vse8.v v8, (a3)
 ; CHECK-NEXT:    add a3, a3, a4