[PATCH] D56074: [NFC] Add detector function for explicitly expressed guards

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added reviewers: anna, apilipenko, skatkov, reames.

This patch adds a function to detect guards expressed in explicit form:

    %wc = call i1 @llvm.experimental.widenable.condition()
    %guard_cond = and i1, %some_cond, %wc
    br i1 %guard_cond, label %guarded, label %deopt
  
  deopt:
    <maybe some non-side-effecting instructions>
    deoptimize()

This form can be used as alternative to implicit control flow guard
representation expressed by `experimental_guard` intrinsic.


https://reviews.llvm.org/D56074

Files:
  include/llvm/Analysis/GuardUtils.h
  lib/Analysis/GuardUtils.cpp


Index: lib/Analysis/GuardUtils.cpp
===================================================================
--- lib/Analysis/GuardUtils.cpp
+++ lib/Analysis/GuardUtils.cpp
@@ -19,3 +19,30 @@
   using namespace llvm::PatternMatch;
   return match(U, m_Intrinsic<Intrinsic::experimental_guard>());
 }
+
+bool llvm::isExplicitGuard(const User *U) {
+  using namespace llvm::PatternMatch;
+  const BranchInst *BI = dyn_cast<BranchInst>(U);
+
+  // We are looking for the following pattern:
+  //   br i1 %cond & widenable_condition(), label %guarded, label %deopt
+  // deopt:
+  //   <non-side-effecting instructions>
+  //   deoptimize()
+  if (!BI || !BI->isConditional())
+    return false;
+
+  if (!match(BI->getCondition(),
+             m_And(m_Value(),
+                   m_Intrinsic<Intrinsic::experimental_widenable_condition>())))
+    return false;
+
+  const BasicBlock *DeoptBlock = BI->getSuccessor(1);
+  for (auto &Insn : *DeoptBlock) {
+    if (match(&Insn, m_Intrinsic<Intrinsic::experimental_deoptimize>()))
+      return true;
+    if (Insn.mayHaveSideEffects())
+      return false;
+  }
+  return false;
+}
Index: include/llvm/Analysis/GuardUtils.h
===================================================================
--- include/llvm/Analysis/GuardUtils.h
+++ include/llvm/Analysis/GuardUtils.h
@@ -20,6 +20,9 @@
 /// Returns true iff \p U has semantics of a guard.
 bool isGuard(const User *U);
 
+/// Returns true iff \p U is a branch that has semantics of a guard.
+bool isExplicitGuard(const User *U);
+
 } // llvm
 
 #endif // LLVM_ANALYSIS_GUARDUTILS_H


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