[PATCH] D131646: [clang][dataflow] Restructure loops to call widen on back edges

[Stanislav Gatev via Phabricator via cfe-commits]

sgatev added inline comments.


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Comment at: clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp:157
 
+// Returns whether `Block` is a "back edge" in the CFG. Such a block has only
+// one successor, the start of the loop.
----------------
Let's start function comments with `///` throughout the file.


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Comment at: clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp:164
+
+// Returns the predecessor to `Block` that is a "back edge", if one exists.
+//
----------------



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Comment at: clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp:167-168
+// If this function returns a non-null pointer, that means `Block` dominates the
+// back edge block. (That is, all paths from the entry block to the back edge
+// block must go through `Block`.) It also means that there are only two
+// predecessors; the other is along the path from the entry block to `Block`.
----------------



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Comment at: clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp:168-169
+// back edge block. (That is, all paths from the entry block to the back edge
+// block must go through `Block`.) It also means that there are only two
+// predecessors; the other is along the path from the entry block to `Block`.
+static const CFGBlock *findBackEdge(const CFGBlock *Block) {
----------------
li.zhe.hua wrote:
> xazax.hun wrote:
> > Is this also true when we have multiple `continue` statements in the loop?
> Yes. The end of the loop, and each of the `continue` statements, target the back edge block. They all get funneled through that back edge to `Block`, such that `Block` only has two predecessors. However, I haven't verified this in the CFG code, only by not finding a counterexample.
Does that hold for back edges stemming from `goto` statements?


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Comment at: clang/unittests/Analysis/FlowSensitive/TypeErasedDataflowAnalysisTest.cpp:270
+
+TEST(DataflowAnalysisTest, ConvergesOnWidenAnalysis) {
+  std::string Code = R"(
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There's already a set of "widening" tests - http://google3/third_party/llvm/llvm-project/clang/unittests/Analysis/FlowSensitive/TypeErasedDataflowAnalysisTest.cpp;l=527-712;rcl=462638952

What do you think about refactoring those so that we have tests that exercise the framework with both `join` and `widen`?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D131646/new/

https://reviews.llvm.org/D131646