[DAG] visitFREEZE - limit freezing of multiple operands

This is a partial revert of #145939 (I've kept the BUILD_VECTOR(FREEZE(UNDEF), FREEZE(UNDEF), elt2, ...) canonicalization) as we're getting reports of infinite loops (#148084).

The issue appears to be due to deep chains of nodes and how visitFREEZE replaces all instances of a node with a common frozen version - the other users then get added back to the worklist but might no longer be able to confirm a node isn't poison due to recursion depth limits on isGuaranteedNotToBeUndefOrPoison.

The issue still exists with the old implementation but by only allowing a single frozen operand it helps prevent cases of interdependent frozen nodes.

I'm still working on supporting multiple operands as its critical for topological DAG handling but need to get a fix in for trunk and 21.x.

Author: RKSimon

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -16738,14 +16738,27 @@ SDValue DAGCombiner::visitFREEZE(SDNode *N) {
   // Fold freeze(op(x, ...)) -> op(freeze(x), ...).
   // Try to push freeze through instructions that propagate but don't produce
   // poison as far as possible. If an operand of freeze follows three
-  // conditions 1) one-use, and 2) does not produce poison then push
+  // conditions 1) one-use, 2) does not produce poison, and 3) has all but one
+  // guaranteed-non-poison operands (or is a BUILD_VECTOR or similar) then push
   // the freeze through to the operands that are not guaranteed non-poison.
   // NOTE: we will strip poison-generating flags, so ignore them here.
   if (DAG.canCreateUndefOrPoison(N0, /*PoisonOnly*/ false,
                                  /*ConsiderFlags*/ false) ||
       N0->getNumValues() != 1 || !N0->hasOneUse())
     return SDValue();
 
+  // TOOD: we should always allow multiple operands, however this increases the
+  // likelihood of infinite loops due to the ReplaceAllUsesOfValueWith call
+  // below causing later nodes that share frozen operands to fold again and no
+  // longer being able to confirm other operands are not poison due to recursion
+  // depth limits on isGuaranteedNotToBeUndefOrPoison.
+  bool AllowMultipleMaybePoisonOperands =
+      N0.getOpcode() == ISD::SELECT_CC || N0.getOpcode() == ISD::SETCC ||
+      N0.getOpcode() == ISD::BUILD_VECTOR ||
+      N0.getOpcode() == ISD::BUILD_PAIR ||
+      N0.getOpcode() == ISD::VECTOR_SHUFFLE ||
+      N0.getOpcode() == ISD::CONCAT_VECTORS || N0.getOpcode() == ISD::FMUL;
+
   // Avoid turning a BUILD_VECTOR that can be recognized as "all zeros", "all
   // ones" or "constant" into something that depends on FrozenUndef. We can
   // instead pick undef values to keep those properties, while at the same time
@@ -16772,8 +16785,16 @@ SDValue DAGCombiner::visitFREEZE(SDNode *N) {
     if (DAG.isGuaranteedNotToBeUndefOrPoison(Op, /*PoisonOnly*/ false,
                                              /*Depth*/ 1))
       continue;
-    if (MaybePoisonOperands.insert(Op).second)
+    bool HadMaybePoisonOperands = !MaybePoisonOperands.empty();
+    bool IsNewMaybePoisonOperand = MaybePoisonOperands.insert(Op).second;
+    if (IsNewMaybePoisonOperand)
       MaybePoisonOperandNumbers.push_back(OpNo);
+    if (!HadMaybePoisonOperands)
+      continue;
+    if (IsNewMaybePoisonOperand && !AllowMultipleMaybePoisonOperands) {
+      // Multiple maybe-poison ops when not allowed - bail out.
+      return SDValue();
+    }
   }
   // NOTE: the whole op may be not guaranteed to not be undef or poison because
   // it could create undef or poison due to it's poison-generating flags.

llvm/test/CodeGen/AMDGPU/amdgpu-codegenprepare-idiv.ll

@@ -7791,7 +7791,7 @@ define amdgpu_kernel void @sdiv_i64_pow2_shl_denom(ptr addrspace(1) %out, i64 %x
 ;
 ; GFX6-LABEL: sdiv_i64_pow2_shl_denom:
 ; GFX6:       ; %bb.0:
-; GFX6-NEXT:    s_load_dwordx2 s[0:1], s[4:5], 0xd
+; GFX6-NEXT:    s_load_dword s0, s[4:5], 0xd
 ; GFX6-NEXT:    s_mov_b32 s7, 0xf000
 ; GFX6-NEXT:    s_mov_b32 s6, -1
 ; GFX6-NEXT:    s_waitcnt lgkmcnt(0)
@@ -7927,7 +7927,7 @@ define amdgpu_kernel void @sdiv_i64_pow2_shl_denom(ptr addrspace(1) %out, i64 %x
 ;
 ; GFX9-LABEL: sdiv_i64_pow2_shl_denom:
 ; GFX9:       ; %bb.0:
-; GFX9-NEXT:    s_load_dwordx2 s[0:1], s[4:5], 0x34
+; GFX9-NEXT:    s_load_dword s0, s[4:5], 0x34
 ; GFX9-NEXT:    s_load_dwordx4 s[8:11], s[4:5], 0x24
 ; GFX9-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX9-NEXT:    s_lshl_b64 s[0:1], 0x1000, s0
@@ -8982,7 +8982,7 @@ define amdgpu_kernel void @srem_i64_pow2_shl_denom(ptr addrspace(1) %out, i64 %x
 ;
 ; GFX6-LABEL: srem_i64_pow2_shl_denom:
 ; GFX6:       ; %bb.0:
-; GFX6-NEXT:    s_load_dwordx2 s[0:1], s[4:5], 0xd
+; GFX6-NEXT:    s_load_dword s0, s[4:5], 0xd
 ; GFX6-NEXT:    s_mov_b32 s7, 0xf000
 ; GFX6-NEXT:    s_mov_b32 s6, -1
 ; GFX6-NEXT:    s_waitcnt lgkmcnt(0)
@@ -9116,7 +9116,7 @@ define amdgpu_kernel void @srem_i64_pow2_shl_denom(ptr addrspace(1) %out, i64 %x
 ;
 ; GFX9-LABEL: srem_i64_pow2_shl_denom:
 ; GFX9:       ; %bb.0:
-; GFX9-NEXT:    s_load_dwordx2 s[0:1], s[4:5], 0x34
+; GFX9-NEXT:    s_load_dword s0, s[4:5], 0x34
 ; GFX9-NEXT:    s_load_dwordx4 s[8:11], s[4:5], 0x24
 ; GFX9-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX9-NEXT:    s_lshl_b64 s[0:1], 0x1000, s0

llvm/test/CodeGen/AMDGPU/div_i128.ll

@@ -475,28 +475,21 @@ define i128 @v_sdiv_i128_vv(i128 %lhs, i128 %rhs) {
 ; GFX9-O0-NEXT:    ; implicit-def: $sgpr8
 ; GFX9-O0-NEXT:    ; kill: def $vgpr4 killed $vgpr4 def $vgpr4_vgpr5 killed $exec
 ; GFX9-O0-NEXT:    v_mov_b32_e32 v5, v8
+; GFX9-O0-NEXT:    buffer_store_dword v4, off, s[0:3], s32 offset:28 ; 4-byte Folded Spill
+; GFX9-O0-NEXT:    s_nop 0
+; GFX9-O0-NEXT:    buffer_store_dword v5, off, s[0:3], s32 offset:32 ; 4-byte Folded Spill
 ; GFX9-O0-NEXT:    ; implicit-def: $sgpr8
 ; GFX9-O0-NEXT:    ; implicit-def: $sgpr8
 ; GFX9-O0-NEXT:    ; kill: def $vgpr7 killed $vgpr7 def $vgpr7_vgpr8 killed $exec
 ; GFX9-O0-NEXT:    v_mov_b32_e32 v8, v6
-; GFX9-O0-NEXT:    v_mov_b32_e32 v10, v8
-; GFX9-O0-NEXT:    v_mov_b32_e32 v9, v7
-; GFX9-O0-NEXT:    buffer_store_dword v9, off, s[0:3], s32 offset:28 ; 4-byte Folded Spill
-; GFX9-O0-NEXT:    s_nop 0
-; GFX9-O0-NEXT:    buffer_store_dword v10, off, s[0:3], s32 offset:32 ; 4-byte Folded Spill
-; GFX9-O0-NEXT:    v_mov_b32_e32 v10, v5
-; GFX9-O0-NEXT:    v_mov_b32_e32 v9, v4
-; GFX9-O0-NEXT:    buffer_store_dword v9, off, s[0:3], s32 offset:20 ; 4-byte Folded Spill
+; GFX9-O0-NEXT:    buffer_store_dword v7, off, s[0:3], s32 offset:20 ; 4-byte Folded Spill
 ; GFX9-O0-NEXT:    s_nop 0
-; GFX9-O0-NEXT:    buffer_store_dword v10, off, s[0:3], s32 offset:24 ; 4-byte Folded Spill
-; GFX9-O0-NEXT:    s_mov_b64 s[8:9], s[6:7]
-; GFX9-O0-NEXT:    v_cmp_eq_u64_e64 s[8:9], v[7:8], s[8:9]
+; GFX9-O0-NEXT:    buffer_store_dword v8, off, s[0:3], s32 offset:24 ; 4-byte Folded Spill
+; GFX9-O0-NEXT:    v_cmp_eq_u64_e64 s[8:9], v[7:8], s[6:7]
 ; GFX9-O0-NEXT:    s_mov_b64 s[12:13], 0x7f
-; GFX9-O0-NEXT:    s_mov_b64 s[14:15], s[12:13]
-; GFX9-O0-NEXT:    v_cmp_gt_u64_e64 s[14:15], v[4:5], s[14:15]
+; GFX9-O0-NEXT:    v_cmp_gt_u64_e64 s[14:15], v[4:5], s[12:13]
 ; GFX9-O0-NEXT:    v_cndmask_b32_e64 v9, 0, 1, s[14:15]
-; GFX9-O0-NEXT:    s_mov_b64 s[14:15], s[6:7]
-; GFX9-O0-NEXT:    v_cmp_ne_u64_e64 s[14:15], v[7:8], s[14:15]
+; GFX9-O0-NEXT:    v_cmp_ne_u64_e64 s[14:15], v[7:8], s[6:7]
 ; GFX9-O0-NEXT:    v_cndmask_b32_e64 v6, 0, 1, s[14:15]
 ; GFX9-O0-NEXT:    v_cndmask_b32_e64 v6, v6, v9, s[8:9]
 ; GFX9-O0-NEXT:    v_and_b32_e64 v6, 1, v6
@@ -507,7 +500,6 @@ define i128 @v_sdiv_i128_vv(i128 %lhs, i128 %rhs) {
 ; GFX9-O0-NEXT:    v_mov_b32_e32 v6, v5
 ; GFX9-O0-NEXT:    s_mov_b32 s14, s13
 ; GFX9-O0-NEXT:    v_xor_b32_e64 v6, v6, s14
-; GFX9-O0-NEXT:    ; kill: def $vgpr4 killed $vgpr4 killed $vgpr4_vgpr5 killed $exec
 ; GFX9-O0-NEXT:    ; kill: def $sgpr12 killed $sgpr12 killed $sgpr12_sgpr13
 ; GFX9-O0-NEXT:    v_xor_b32_e64 v4, v4, s12
 ; GFX9-O0-NEXT:    ; kill: def $vgpr4 killed $vgpr4 def $vgpr4_vgpr5 killed $exec
@@ -1046,10 +1038,10 @@ define i128 @v_sdiv_i128_vv(i128 %lhs, i128 %rhs) {
 ; GFX9-O0-NEXT:    buffer_load_dword v7, off, s[0:3], s32 offset:40 ; 4-byte Folded Reload
 ; GFX9-O0-NEXT:    buffer_load_dword v10, off, s[0:3], s32 offset:44 ; 4-byte Folded Reload
 ; GFX9-O0-NEXT:    buffer_load_dword v11, off, s[0:3], s32 offset:48 ; 4-byte Folded Reload
-; GFX9-O0-NEXT:    buffer_load_dword v4, off, s[0:3], s32 offset:28 ; 4-byte Folded Reload
-; GFX9-O0-NEXT:    buffer_load_dword v5, off, s[0:3], s32 offset:32 ; 4-byte Folded Reload
-; GFX9-O0-NEXT:    buffer_load_dword v0, off, s[0:3], s32 offset:20 ; 4-byte Folded Reload
-; GFX9-O0-NEXT:    buffer_load_dword v1, off, s[0:3], s32 offset:24 ; 4-byte Folded Reload
+; GFX9-O0-NEXT:    buffer_load_dword v4, off, s[0:3], s32 offset:20 ; 4-byte Folded Reload
+; GFX9-O0-NEXT:    buffer_load_dword v5, off, s[0:3], s32 offset:24 ; 4-byte Folded Reload
+; GFX9-O0-NEXT:    buffer_load_dword v0, off, s[0:3], s32 offset:28 ; 4-byte Folded Reload
+; GFX9-O0-NEXT:    buffer_load_dword v1, off, s[0:3], s32 offset:32 ; 4-byte Folded Reload
 ; GFX9-O0-NEXT:    s_mov_b64 s[6:7], 1
 ; GFX9-O0-NEXT:    s_mov_b32 s5, s6
 ; GFX9-O0-NEXT:    s_waitcnt vmcnt(1)
@@ -2667,28 +2659,21 @@ define i128 @v_udiv_i128_vv(i128 %lhs, i128 %rhs) {
 ; GFX9-O0-NEXT:    ; implicit-def: $sgpr8
 ; GFX9-O0-NEXT:    ; kill: def $vgpr4 killed $vgpr4 def $vgpr4_vgpr5 killed $exec
 ; GFX9-O0-NEXT:    v_mov_b32_e32 v5, v8
+; GFX9-O0-NEXT:    buffer_store_dword v4, off, s[0:3], s32 offset:28 ; 4-byte Folded Spill
+; GFX9-O0-NEXT:    s_nop 0
+; GFX9-O0-NEXT:    buffer_store_dword v5, off, s[0:3], s32 offset:32 ; 4-byte Folded Spill
 ; GFX9-O0-NEXT:    ; implicit-def: $sgpr8
 ; GFX9-O0-NEXT:    ; implicit-def: $sgpr8
 ; GFX9-O0-NEXT:    ; kill: def $vgpr7 killed $vgpr7 def $vgpr7_vgpr8 killed $exec
 ; GFX9-O0-NEXT:    v_mov_b32_e32 v8, v6
-; GFX9-O0-NEXT:    v_mov_b32_e32 v10, v8
-; GFX9-O0-NEXT:    v_mov_b32_e32 v9, v7
-; GFX9-O0-NEXT:    buffer_store_dword v9, off, s[0:3], s32 offset:28 ; 4-byte Folded Spill
-; GFX9-O0-NEXT:    s_nop 0
-; GFX9-O0-NEXT:    buffer_store_dword v10, off, s[0:3], s32 offset:32 ; 4-byte Folded Spill
-; GFX9-O0-NEXT:    v_mov_b32_e32 v10, v5
-; GFX9-O0-NEXT:    v_mov_b32_e32 v9, v4
-; GFX9-O0-NEXT:    buffer_store_dword v9, off, s[0:3], s32 offset:20 ; 4-byte Folded Spill
+; GFX9-O0-NEXT:    buffer_store_dword v7, off, s[0:3], s32 offset:20 ; 4-byte Folded Spill
 ; GFX9-O0-NEXT:    s_nop 0
-; GFX9-O0-NEXT:    buffer_store_dword v10, off, s[0:3], s32 offset:24 ; 4-byte Folded Spill
-; GFX9-O0-NEXT:    s_mov_b64 s[8:9], s[6:7]
-; GFX9-O0-NEXT:    v_cmp_eq_u64_e64 s[8:9], v[7:8], s[8:9]
+; GFX9-O0-NEXT:    buffer_store_dword v8, off, s[0:3], s32 offset:24 ; 4-byte Folded Spill
+; GFX9-O0-NEXT:    v_cmp_eq_u64_e64 s[8:9], v[7:8], s[6:7]
 ; GFX9-O0-NEXT:    s_mov_b64 s[12:13], 0x7f
-; GFX9-O0-NEXT:    s_mov_b64 s[14:15], s[12:13]
-; GFX9-O0-NEXT:    v_cmp_gt_u64_e64 s[14:15], v[4:5], s[14:15]
+; GFX9-O0-NEXT:    v_cmp_gt_u64_e64 s[14:15], v[4:5], s[12:13]
 ; GFX9-O0-NEXT:    v_cndmask_b32_e64 v9, 0, 1, s[14:15]
-; GFX9-O0-NEXT:    s_mov_b64 s[14:15], s[6:7]
-; GFX9-O0-NEXT:    v_cmp_ne_u64_e64 s[14:15], v[7:8], s[14:15]
+; GFX9-O0-NEXT:    v_cmp_ne_u64_e64 s[14:15], v[7:8], s[6:7]
 ; GFX9-O0-NEXT:    v_cndmask_b32_e64 v6, 0, 1, s[14:15]
 ; GFX9-O0-NEXT:    v_cndmask_b32_e64 v6, v6, v9, s[8:9]
 ; GFX9-O0-NEXT:    v_and_b32_e64 v6, 1, v6
@@ -2699,7 +2684,6 @@ define i128 @v_udiv_i128_vv(i128 %lhs, i128 %rhs) {
 ; GFX9-O0-NEXT:    v_mov_b32_e32 v6, v5
 ; GFX9-O0-NEXT:    s_mov_b32 s14, s13
 ; GFX9-O0-NEXT:    v_xor_b32_e64 v6, v6, s14
-; GFX9-O0-NEXT:    ; kill: def $vgpr4 killed $vgpr4 killed $vgpr4_vgpr5 killed $exec
 ; GFX9-O0-NEXT:    ; kill: def $sgpr12 killed $sgpr12 killed $sgpr12_sgpr13
 ; GFX9-O0-NEXT:    v_xor_b32_e64 v4, v4, s12
 ; GFX9-O0-NEXT:    ; kill: def $vgpr4 killed $vgpr4 def $vgpr4_vgpr5 killed $exec
@@ -3238,10 +3222,10 @@ define i128 @v_udiv_i128_vv(i128 %lhs, i128 %rhs) {
 ; GFX9-O0-NEXT:    buffer_load_dword v7, off, s[0:3], s32 offset:40 ; 4-byte Folded Reload
 ; GFX9-O0-NEXT:    buffer_load_dword v10, off, s[0:3], s32 offset:44 ; 4-byte Folded Reload
 ; GFX9-O0-NEXT:    buffer_load_dword v11, off, s[0:3], s32 offset:48 ; 4-byte Folded Reload
-; GFX9-O0-NEXT:    buffer_load_dword v4, off, s[0:3], s32 offset:28 ; 4-byte Folded Reload
-; GFX9-O0-NEXT:    buffer_load_dword v5, off, s[0:3], s32 offset:32 ; 4-byte Folded Reload
-; GFX9-O0-NEXT:    buffer_load_dword v0, off, s[0:3], s32 offset:20 ; 4-byte Folded Reload
-; GFX9-O0-NEXT:    buffer_load_dword v1, off, s[0:3], s32 offset:24 ; 4-byte Folded Reload
+; GFX9-O0-NEXT:    buffer_load_dword v4, off, s[0:3], s32 offset:20 ; 4-byte Folded Reload
+; GFX9-O0-NEXT:    buffer_load_dword v5, off, s[0:3], s32 offset:24 ; 4-byte Folded Reload
+; GFX9-O0-NEXT:    buffer_load_dword v0, off, s[0:3], s32 offset:28 ; 4-byte Folded Reload
+; GFX9-O0-NEXT:    buffer_load_dword v1, off, s[0:3], s32 offset:32 ; 4-byte Folded Reload
 ; GFX9-O0-NEXT:    s_mov_b64 s[6:7], 1
 ; GFX9-O0-NEXT:    s_mov_b32 s5, s6
 ; GFX9-O0-NEXT:    s_waitcnt vmcnt(1)