[StructurizeCFG] nested-if zerocost hoist bugfix

llvm/lib/Transforms/Scalar/StructurizeCFG.cpp

@@ -997,7 +997,8 @@ void StructurizeCFG::simplifyHoistedPhis() {
         continue;
 
       OtherPhi->setIncomingValue(PoisonValBBIdx, V);
-      Phi->setIncomingValue(i, OtherV);
+      if (DT->dominates(OtherV, Phi))
+        Phi->setIncomingValue(i, OtherV);
     }
   }
 }

llvm/test/CodeGen/AMDGPU/structurize-hoist.ll

@@ -178,3 +178,56 @@ latch:
 end:
   ret void
 }
+
+define void @test_nested_if(ptr %ptr, i32 %val, i1 %cond) {
+; GFX900-LABEL: test_nested_if:
+; GFX900:       ; %bb.0: ; %entry
+; GFX900-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; GFX900-NEXT:    flat_load_dword v2, v[0:1]
+; GFX900-NEXT:    v_and_b32_e32 v3, 1, v3
+; GFX900-NEXT:    v_cmp_eq_u32_e64 s[4:5], 1, v3
+; GFX900-NEXT:    s_mov_b64 s[8:9], -1
+; GFX900-NEXT:    s_xor_b64 s[10:11], s[4:5], -1
+; GFX900-NEXT:    s_and_saveexec_b64 s[6:7], s[10:11]
+; GFX900-NEXT:    s_cbranch_execz .LBB3_4
+; GFX900-NEXT:  ; %bb.1: ; %then
+; GFX900-NEXT:    s_and_saveexec_b64 s[12:13], s[10:11]
+; GFX900-NEXT:    s_cbranch_execz .LBB3_3
+; GFX900-NEXT:  ; %bb.2: ; %then_2
+; GFX900-NEXT:    s_waitcnt vmcnt(0) lgkmcnt(0)
+; GFX900-NEXT:    flat_load_dword v2, v[0:1]
+; GFX900-NEXT:    s_xor_b64 s[8:9], exec, -1
+; GFX900-NEXT:  .LBB3_3: ; %Flow1
+; GFX900-NEXT:    s_or_b64 exec, exec, s[12:13]
+; GFX900-NEXT:    s_andn2_b64 s[4:5], s[4:5], exec
+; GFX900-NEXT:    s_and_b64 s[8:9], s[8:9], exec
+; GFX900-NEXT:    s_or_b64 s[4:5], s[4:5], s[8:9]
+; GFX900-NEXT:  .LBB3_4: ; %Flow
+; GFX900-NEXT:    s_or_b64 exec, exec, s[6:7]
+; GFX900-NEXT:    s_and_saveexec_b64 s[6:7], s[4:5]
+; GFX900-NEXT:    s_or_b64 exec, exec, s[6:7]
+; GFX900-NEXT:    s_waitcnt vmcnt(0) lgkmcnt(0)
+; GFX900-NEXT:    flat_store_dword v[0:1], v2
+; GFX900-NEXT:    s_waitcnt vmcnt(0) lgkmcnt(0)
+; GFX900-NEXT:    s_setpc_b64 s[30:31]
+entry:
+  %load_then = load %pair, ptr %ptr
+  br i1 %cond, label %else, label %then
+
+then:
+  %a16 = icmp slt i32  %val, 255
+  br i1 %cond, label %else, label %then_2
+
+then_2:
+  %loaded = load i32, ptr  %ptr
+  br label %merge
+
+else:
+  %a_else = extractvalue %pair %load_then, 0
+  br label %merge
+
+merge:
+  %phi = phi i32  [ %loaded, %then_2 ], [ %a_else, %else ]
+  store i32 %phi, ptr  %ptr
+  ret void
+}

llvm/test/Transforms/StructurizeCFG/hoist-zerocost.ll

@@ -159,3 +159,53 @@ latch:
 end:
   ret void
 }
+
+define void @test_nested_if(ptr %ptr, i32 %val, i1 %cond) {
+; CHECK-LABEL: define void @test_nested_if(
+; CHECK-SAME: ptr [[PTR:%.*]], i32 [[VAL:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[COND_INV:%.*]] = xor i1 [[COND]], true
+; CHECK-NEXT:    [[LOAD_THEN:%.*]] = load [[PAIR:%.*]], ptr [[PTR]], align 4
+; CHECK-NEXT:    [[A_ELSE:%.*]] = extractvalue [[PAIR]] [[LOAD_THEN]], 0
+; CHECK-NEXT:    br i1 [[COND_INV]], label %[[THEN:.*]], label %[[FLOW:.*]]
+; CHECK:       [[THEN]]:
+; CHECK-NEXT:    [[A16:%.*]] = icmp slt i32 [[VAL]], 255
+; CHECK-NEXT:    br i1 [[COND_INV]], label %[[THEN_2:.*]], label %[[FLOW1:.*]]
+; CHECK:       [[FLOW]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = phi i32 [ [[TMP2:%.*]], %[[FLOW1]] ], [ [[A_ELSE]], %[[ENTRY]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = phi i1 [ [[TMP3:%.*]], %[[FLOW1]] ], [ [[COND]], %[[ENTRY]] ]
+; CHECK-NEXT:    br i1 [[TMP1]], label %[[ELSE:.*]], label %[[MERGE:.*]]
+; CHECK:       [[THEN_2]]:
+; CHECK-NEXT:    [[LOADED:%.*]] = load i32, ptr [[PTR]], align 4
+; CHECK-NEXT:    br label %[[FLOW1]]
+; CHECK:       [[FLOW1]]:
+; CHECK-NEXT:    [[TMP2]] = phi i32 [ [[LOADED]], %[[THEN_2]] ], [ [[A_ELSE]], %[[THEN]] ]
+; CHECK-NEXT:    [[TMP3]] = phi i1 [ false, %[[THEN_2]] ], [ true, %[[THEN]] ]
+; CHECK-NEXT:    br label %[[FLOW]]
+; CHECK:       [[ELSE]]:
+; CHECK-NEXT:    br label %[[MERGE]]
+; CHECK:       [[MERGE]]:
+; CHECK-NEXT:    store i32 [[TMP0]], ptr [[PTR]], align 4
+; CHECK-NEXT:    ret void
+;
+entry:
+  %load_then = load %pair, ptr %ptr
+  br i1 %cond, label %else, label %then
+
+then:
+  %a16 = icmp slt i32  %val, 255
+  br i1 %cond, label %else, label %then_2
+
+then_2:
+  %loaded = load i32, ptr  %ptr
+  br label %merge
+
+else:
+  %a_else = extractvalue %pair %load_then, 0
+  br label %merge
+
+merge:
+  %phi = phi i32  [ %loaded, %then_2 ], [ %a_else, %else ]
+  store i32 %phi, ptr  %ptr
+  ret void
+}