[DAGCombiner] Allow freeze to sink through fmul by adding it to AllowMultipleMaybePoisonOperands (#142250)

Allow freeze to sink through fmul by treating it as a
non-poison-generating op
when operands are not poison.

Adding `ISD::FMUL` to `AllowMultipleMaybePoisonOperands` lets DAG
combine
push freeze through fmul. This helps expose patterns like `fmul+fadd`
for `FMA` fusion.

When rebuilding the node, we drop flags like nnan/ninf/nsz that imply
poison,
but keep contract, reassoc, afn, and arcp.


Closes: #141622

Author: harrisonGPU

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -16392,12 +16392,11 @@ SDValue DAGCombiner::visitFREEZE(SDNode *N) {
     return SDValue();
 
   bool AllowMultipleMaybePoisonOperands =
-      N0.getOpcode() == ISD::SELECT_CC ||
-      N0.getOpcode() == ISD::SETCC ||
+      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::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
@@ -16495,7 +16494,17 @@ SDValue DAGCombiner::visitFREEZE(SDNode *N) {
                              SVN->getMask());
   } else {
     // NOTE: this strips poison generating flags.
-    R = DAG.getNode(N0.getOpcode(), SDLoc(N0), N0->getVTList(), Ops);
+    // Folding freeze(op(x, ...)) -> op(freeze(x), ...) does not require nnan,
+    // ninf, nsz, or fast.
+    // However, contract, reassoc, afn, and arcp should be preserved,
+    // as these fast-math flags do not introduce poison values.
+    SDNodeFlags SrcFlags = N0->getFlags();
+    SDNodeFlags SafeFlags;
+    SafeFlags.setAllowContract(SrcFlags.hasAllowContract());
+    SafeFlags.setAllowReassociation(SrcFlags.hasAllowReassociation());
+    SafeFlags.setApproximateFuncs(SrcFlags.hasApproximateFuncs());
+    SafeFlags.setAllowReciprocal(SrcFlags.hasAllowReciprocal());
+    R = DAG.getNode(N0.getOpcode(), SDLoc(N0), N0->getVTList(), Ops, SafeFlags);
   }
   assert(DAG.isGuaranteedNotToBeUndefOrPoison(R, /*PoisonOnly*/ false) &&
          "Can't create node that may be undef/poison!");

llvm/test/CodeGen/AMDGPU/fold-freeze-fmul-to-fma.ll

@@ -17,9 +17,7 @@ define float @fma_from_freeze_mul_add_left_with_nnan(float %x, float %y) {
 ; CHECK-LABEL: fma_from_freeze_mul_add_left_with_nnan:
 ; CHECK:       ; %bb.0:
 ; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; CHECK-NEXT:    v_mul_f32_e32 v0, v0, v1
-; CHECK-NEXT:    s_delay_alu instid0(VALU_DEP_1)
-; CHECK-NEXT:    v_add_f32_e32 v0, 1.0, v0
+; CHECK-NEXT:    v_fma_f32 v0, v0, v1, 1.0
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
   %mul = fmul nnan contract afn float %x, %y
   %mul.fr = freeze float %mul
@@ -43,9 +41,7 @@ define float @fma_from_freeze_mul_add_right_with_nnan(float %x, float %y) {
 ; CHECK-LABEL: fma_from_freeze_mul_add_right_with_nnan:
 ; CHECK:       ; %bb.0:
 ; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; CHECK-NEXT:    v_mul_f32_e32 v0, v0, v1
-; CHECK-NEXT:    s_delay_alu instid0(VALU_DEP_1)
-; CHECK-NEXT:    v_add_f32_e32 v0, 1.0, v0
+; CHECK-NEXT:    v_fma_f32 v0, v0, v1, 1.0
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
   %mul = fmul nnan contract float %x, %y
   %mul.fr = freeze float %mul
@@ -69,9 +65,7 @@ define float @fma_from_freeze_mul_sub_left_with_nnan(float %x, float %y) {
 ; CHECK-LABEL: fma_from_freeze_mul_sub_left_with_nnan:
 ; CHECK:       ; %bb.0:
 ; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; CHECK-NEXT:    v_mul_f32_e32 v0, v0, v1
-; CHECK-NEXT:    s_delay_alu instid0(VALU_DEP_1)
-; CHECK-NEXT:    v_add_f32_e32 v0, -1.0, v0
+; CHECK-NEXT:    v_fma_f32 v0, v0, v1, -1.0
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
   %mul = fmul nnan contract float %x, %y
   %mul.fr = freeze float %mul
@@ -95,12 +89,42 @@ define float @fma_from_freeze_mul_sub_right_with_nnan(float %x, float %y) {
 ; CHECK-LABEL: fma_from_freeze_mul_sub_right_with_nnan:
 ; CHECK:       ; %bb.0:
 ; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; CHECK-NEXT:    v_mul_f32_e32 v0, v0, v1
-; CHECK-NEXT:    s_delay_alu instid0(VALU_DEP_1)
-; CHECK-NEXT:    v_sub_f32_e32 v0, 1.0, v0
+; CHECK-NEXT:    v_fma_f32 v0, -v0, v1, 1.0
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
   %mul = fmul nnan contract float %x, %y
   %mul.fr = freeze float %mul
   %sub = fsub nnan contract float 1.000000e+00, %mul.fr
   ret float %sub
 }
+
+define float @fma_freeze_sink_multiple_maybe_poison_nnan_add(float %x, float %y) {
+; CHECK-LABEL: fma_freeze_sink_multiple_maybe_poison_nnan_add:
+; CHECK:       ; %bb.0:
+; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; CHECK-NEXT:    v_dual_subrev_f32 v0, 1.0, v0 :: v_dual_add_f32 v1, 1.0, v1
+; CHECK-NEXT:    s_delay_alu instid0(VALU_DEP_1)
+; CHECK-NEXT:    v_fma_f32 v0, v0, v1, 1.0
+; CHECK-NEXT:    s_setpc_b64 s[30:31]
+  %fsub_x = fsub nnan contract float %x, 1.000000e+00
+  %fadd_y = fadd nnan contract float %y, 1.000000e+00
+  %mul = fmul nnan contract float %fsub_x, %fadd_y
+  %mul.fr = freeze float %mul
+  %add = fadd nnan contract float %mul.fr, 1.000000e+00
+  ret float %add
+}
+
+define float @fma_freeze_sink_multiple_maybe_poison_nnan_sub(float %x, float %y) {
+; CHECK-LABEL: fma_freeze_sink_multiple_maybe_poison_nnan_sub:
+; CHECK:       ; %bb.0:
+; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; CHECK-NEXT:    v_dual_add_f32 v0, 1.0, v0 :: v_dual_add_f32 v1, -1.0, v1
+; CHECK-NEXT:    s_delay_alu instid0(VALU_DEP_1)
+; CHECK-NEXT:    v_fma_f32 v0, v0, v1, -1.0
+; CHECK-NEXT:    s_setpc_b64 s[30:31]
+  %fadd_x = fadd nnan contract float %x, 1.000000e+00
+  %fsub_y = fsub nnan contract float %y, 1.000000e+00
+  %mul = fmul nnan contract float %fadd_x, %fsub_y
+  %mul.fr = freeze float %mul
+  %sub = fsub nnan contract float %mul.fr, 1.000000e+00
+  ret float %sub
+}