[PM] Introduce an analysis set used to preserve all analyses over

a function's CFG when that CFG is unchanged.

This allows transformation passes to simply claim they preserve the CFG
and analysis passes to check for the CFG being preserved to remove the
fanout of all analyses being listed in all passes.

I've gone through and removed or cleaned up as many of the comments
reminding us to do this as I could.

Differential Revision: https://reviews.llvm.org/D28627

llvm-svn: 292054

1 files changed, 1 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 8ba19fd02f8..f6d1a1e9664 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3176,10 +3176,9 @@ PreservedAnalyses InstCombinePass::run(Function &F,
     return PreservedAnalyses::all();
 
   // Mark all the analyses that instcombine updates as preserved.
-  // FIXME: This should also 'preserve the CFG'.
   PreservedAnalyses PA;
+  PA.preserveSet<CFGAnalyses>();
   PA.preserve<AAManager>();
-  PA.preserve<DominatorTreeAnalysis>();
   PA.preserve<GlobalsAA>();
   return PA;
 }