[SimplifyCFG][AMDGPU] AMDGPUUnifyDivergentExitNodes: SimplifyCFG isn't ready to prese...

There is a number of transforms in SimplifyCFG that take DomTree out of
DomTreeUpdater, and do updates manually. Until they are fixed,
user passes are unable to claim that PDT is preserved.

Note that the default for SimplifyCFG is still not to preserve DomTree,
so this is still effectively NFC.

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp b/llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
index 96de1bd..9ea8b32 100644 (file)
--- a/llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
@@ -89,7 +89,7 @@ void AMDGPUUnifyDivergentExitNodes::getAnalysisUsage(AnalysisUsage &AU) const{
 
   if (RequireAndPreserveDomTree) {
     AU.addPreserved<DominatorTreeWrapperPass>();
-    AU.addPreserved<PostDominatorTreeWrapperPass>();
+    // FIXME: preserve PostDominatorTreeWrapperPass
   }
 
   // No divergent values are changed, only blocks and branch edges.
@@ -369,7 +369,8 @@ bool AMDGPUUnifyDivergentExitNodes::runOnFunction(Function &F) {
     }
   }
 
-  DomTreeUpdater DTU(DT, &PDT, DomTreeUpdater::UpdateStrategy::Eager);
+  // FIXME: add PDT here once simplifycfg is ready.
+  DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
   if (RequireAndPreserveDomTree)
     DTU.applyUpdates(Updates);
   Updates.clear();

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index e1f7ef6..825de42 100644 (file)
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -263,7 +263,11 @@ public:
                  const DataLayout &DL,
                  SmallPtrSetImpl<BasicBlock *> *LoopHeaders,
                  const SimplifyCFGOptions &Opts)
-      : TTI(TTI), DTU(DTU), DL(DL), LoopHeaders(LoopHeaders), Options(Opts) {}
+      : TTI(TTI), DTU(DTU), DL(DL), LoopHeaders(LoopHeaders), Options(Opts) {
+    assert((!DTU || !DTU->hasPostDomTree()) &&
+           "SimplifyCFG is not yet capable of maintaining validity of a "
+           "PostDomTree, so don't ask for it.");
+  }
 
   bool simplifyOnce(BasicBlock *BB);
   bool simplifyOnceImpl(BasicBlock *BB);