[amdgpu] Fix a crash case when preserving MDT in SILowerControlFlow

[hliao]

Summary

• When a redundant MBB is being erased from MDT, check whether its single successor is dominiated by it. If yes, update that successor's idom before erasing MBB; otherwise, it implies MBB is a leaf node and could be erased directly.

[hliao]

Fix typo.

[hliao]

Revise the comment.

[hliao]

Remove '!llvm.ident' in that test triggering crash.

[foad]

LGTM, thank you!

llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp

if (GetFallThroughSucc(P) == &MBB)
       FallThrough = P;
     P->ReplaceUsesOfBlockWith(&MBB, Succ);
   }
   MBB.removeSuccessor(Succ);
   if (LIS) {
     for (auto &I : MBB.instrs())
       LIS->RemoveMachineInstrFromMaps(I);
   }
-  if (MDT)
+  if (MDT) {
+    // If Succ, the single successor of MBB, is dominated by MBB, MDT needs
+    // updating by changing Succ's idom to the one of MBB; otherwise, MBB must
+    // be a leaf node in MDT and could be erased directly.
+    if (MDT->dominates(&MBB, Succ))
+      MDT->changeImmediateDominator(MDT->getNode(Succ),
+                                    MDT->getNode(&MBB)->getIDom());
     MDT->eraseNode(&MBB);
+  }
   MBB.clear();
   MBB.eraseFromParent();
   if (FallThrough && !FallThrough->isLayoutSuccessor(Succ)) {
     if (!GetFallThroughSucc(Succ)) {
       MachineFunction *MF = FallThrough->getParent();
       MachineFunction::iterator FallThroughPos(FallThrough);
       MF->splice(std::next(FallThroughPos), Succ);
     } else

llvm/test/CodeGen/AMDGPU/mdt-preserving-crash.ll

+; RUN: llc < %s
+target datalayout = "e-p:64:64-p1:64:64-p2:32:32-p3:32:32-p4:64:64-p5:32:32-p6:32:32-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024-v2048:2048-n32:64-S32-A5-G1-ni:7"
+target triple = "amdgcn-amd-amdhsa"
+
+@_RSENC_gDcd_______________________________ = external protected addrspace(1) externally_initialized global [4096 x i8], align 16
+
+define protected amdgpu_kernel void @_RSENC_PRInit__________________________________() local_unnamed_addr #0 {
+entry:
+  %runtimeVersionCopy = alloca [128 x i8], align 16, addrspace(5)
+  %licenseVersionCopy = alloca [128 x i8], align 16, addrspace(5)
+  %pD10 = alloca [128 x i8], align 16, addrspace(5)
+  br label %if.end
+
+if.end:                                           ; preds = %entry
+  %0 = load i32, i32* undef, align 4
+  %mul = mul i32 %0, 3
+  %cmp13 = icmp eq i32 %mul, 989619
+  br i1 %cmp13, label %cleanup.cont, label %if.end15
+
+if.end15:                                         ; preds = %if.end
+  br i1 undef, label %cleanup.cont, label %lor.lhs.false17
+
+lor.lhs.false17:                                  ; preds = %if.end15
+  br label %while.cond.i
+
+while.cond.i:                                     ; preds = %while.cond.i, %lor.lhs.false17
+  switch i32 undef, label %if.end60 [
+    i32 0, label %while.cond.i
+    i32 3, label %if.end60.loopexit857
+  ]
+
+if.end60.loopexit857:                             ; preds = %while.cond.i
+  br label %if.end60
+
+if.end60:                                         ; preds = %if.end60.loopexit857, %while.cond.i
+  %1 = load i8, i8 addrspace(1)* getelementptr inbounds ([4096 x i8], [4096 x i8] addrspace(1)* @_RSENC_gDcd_______________________________, i64 0, i64 655), align 1
+  %2 = getelementptr inbounds [128 x i8], [128 x i8] addrspace(5)* %runtimeVersionCopy, i32 0, i32 0
+  %arrayidx144260.5 = getelementptr inbounds [128 x i8], [128 x i8] addrspace(5)* %runtimeVersionCopy, i32 0, i32 5
+  %3 = getelementptr inbounds [128 x i8], [128 x i8] addrspace(5)* %licenseVersionCopy, i32 0, i32 0
+  %arrayidx156258.5 = getelementptr inbounds [128 x i8], [128 x i8] addrspace(5)* %licenseVersionCopy, i32 0, i32 5
+  switch i8 0, label %if.end5.i [
+    i8 45, label %if.then.i
+    i8 43, label %if.then3.i
+  ]
+
+if.then.i:                                        ; preds = %if.end60
+  unreachable
+
+if.then3.i:                                       ; preds = %if.end60
+  br label %if.end5.i
+
+if.end5.i:                                        ; preds = %if.then3.i, %if.end60
+  %pS.addr.0.i = phi i8 addrspace(5)* [ undef, %if.then3.i ], [ %2, %if.end60 ]
+  %4 = load i8, i8 addrspace(5)* %pS.addr.0.i, align 1
+  %conv612.i = sext i8 %4 to i32
+  %sub13.i = add nsw i32 %conv612.i, -48
+  %cmp714.i = icmp ugt i32 %sub13.i, 9
+  switch i8 undef, label %if.end5.i314 [
+    i8 45, label %if.then.i306
+    i8 43, label %if.then3.i308
+  ]
+
+if.then.i306:                                     ; preds = %if.end5.i
+  unreachable
+
+if.then3.i308:                                    ; preds = %if.end5.i
+  br label %if.end5.i314
+
+if.end5.i314:                                     ; preds = %if.then3.i308, %if.end5.i
+  %pS.addr.0.i309 = phi i8 addrspace(5)* [ undef, %if.then3.i308 ], [ %3, %if.end5.i ]
+  %5 = load i8, i8 addrspace(5)* %pS.addr.0.i309, align 1
+  %conv612.i311 = sext i8 %5 to i32
+  %sub13.i312 = add nsw i32 %conv612.i311, -48
+  %cmp714.i313 = icmp ugt i32 %sub13.i312, 9
+  switch i8 undef, label %if.end5.i338 [
+    i8 45, label %if.then.i330
+    i8 43, label %if.then3.i332
+  ]
+
+if.then.i330:                                     ; preds = %if.end5.i314
+  unreachable
+
+if.then3.i332:                                    ; preds = %if.end5.i314
+  br label %if.end5.i338
+
+if.end5.i338:                                     ; preds = %if.then3.i332, %if.end5.i314
+  %pS.addr.0.i333 = phi i8 addrspace(5)* [ undef, %if.then3.i332 ], [ %arrayidx144260.5, %if.end5.i314 ]
+  %6 = load i8, i8 addrspace(5)* %pS.addr.0.i333, align 1
+  %conv612.i335 = sext i8 %6 to i32
+  %sub13.i336 = add nsw i32 %conv612.i335, -48
+  %cmp714.i337 = icmp ugt i32 %sub13.i336, 9
+  switch i8 undef, label %if.end5.i362 [
+    i8 45, label %if.then.i354
+    i8 43, label %if.then3.i356
+  ]
+
+if.then.i354:                                     ; preds = %if.end5.i338
+  unreachable
+
+if.then3.i356:                                    ; preds = %if.end5.i338
+  br label %if.end5.i362
+
+if.end5.i362:                                     ; preds = %if.then3.i356, %if.end5.i338
+  %pS.addr.0.i357 = phi i8 addrspace(5)* [ undef, %if.then3.i356 ], [ %arrayidx156258.5, %if.end5.i338 ]
+  %7 = load i8, i8 addrspace(5)* %pS.addr.0.i357, align 1
+  %conv612.i359 = sext i8 %7 to i32
+  %sub13.i360 = add nsw i32 %conv612.i359, -48
+  %cmp714.i361 = icmp ugt i32 %sub13.i360, 9
+  store i8 0, i8 addrspace(5)* undef, align 16
+  %8 = load i8, i8 addrspace(1)* getelementptr inbounds ([4096 x i8], [4096 x i8] addrspace(1)* @_RSENC_gDcd_______________________________, i64 0, i64 1153), align 1
+  %arrayidx232250.1 = getelementptr inbounds [128 x i8], [128 x i8] addrspace(5)* %pD10, i32 0, i32 1
+  store i8 %8, i8 addrspace(5)* %arrayidx232250.1, align 1
+  switch i8 undef, label %if.end5.i400 [
+    i8 45, label %if.then.i392
+    i8 43, label %if.then3.i394
+  ]
+
+if.then.i392:                                     ; preds = %if.end5.i362
+  unreachable
+
+if.then3.i394:                                    ; preds = %if.end5.i362
+  br label %if.end5.i400
+
+if.end5.i400:                                     ; preds = %if.then3.i394, %if.end5.i362
+  %pS.addr.0.i395 = phi i8 addrspace(5)* [ %arrayidx232250.1, %if.then3.i394 ], [ undef, %if.end5.i362 ]
+  %9 = load i8, i8 addrspace(5)* %pS.addr.0.i395, align 1
+  %conv612.i397 = sext i8 %9 to i32
+  %sub13.i398 = add nsw i32 %conv612.i397, -48
+  %cmp714.i399 = icmp ugt i32 %sub13.i398, 9
+  %10 = load i8, i8* undef, align 1
+  %cmp9.not.i500 = icmp eq i8 0, %10
+  br label %land.lhs.true402.critedge
+
+land.lhs.true402.critedge:                        ; preds = %if.end5.i400
+  br i1 %cmp9.not.i500, label %if.then404, label %if.else407
+
+if.then404:                                       ; preds = %land.lhs.true402.critedge
+  br label %for.body564
+
+if.else407:                                       ; preds = %land.lhs.true402.critedge
+  br label %if.end570
+
+for.body564:                                      ; preds = %for.body564, %if.then404
+  %i560.0801 = phi i32 [ 0, %if.then404 ], [ %inc568.31, %for.body564 ]
+  %inc568.31 = add nuw nsw i32 %i560.0801, 32
+  %exitcond839.not.31 = icmp eq i32 %inc568.31, 4096
+  br i1 %exitcond839.not.31, label %if.end570, label %for.body564
+
+if.end570:                                        ; preds = %for.body564, %if.else407
+  unreachable
+
+cleanup.cont:                                     ; preds = %if.end15, %if.end
+  ret void
+}
+
+attributes #0 = { "uniform-work-group-size"="true" }