[llvm-branch-commits] [llvm] 7c8b806 - [SimplifyCFG][AMDGPU] AMDGPUUnifyDivergentExitNodes: SimplifyCFG isn't ready to preserve PostDomTree

[Roman Lebedev via llvm-branch-commits]

Author: Roman Lebedev
Date: 2021-01-03T01:45:46+03:00
New Revision: 7c8b8063b66c7b936d41a0c4069c506669e13115

URL: https://github.com/llvm/llvm-project/commit/7c8b8063b66c7b936d41a0c4069c506669e13115
DIFF: https://github.com/llvm/llvm-project/commit/7c8b8063b66c7b936d41a0c4069c506669e13115.diff

LOG: [SimplifyCFG][AMDGPU] AMDGPUUnifyDivergentExitNodes: SimplifyCFG isn't ready to preserve PostDomTree

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.

Added: 
    

Modified: 
    llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
    llvm/lib/Transforms/Utils/SimplifyCFG.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp b/llvm/lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
index 96de1bd8f8d1..9ea8b3265b0d 100644
--- 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 e1f7ef636a89..825de4214c64 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -263,7 +263,11 @@ class SimplifyCFGOpt {
                  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);