[NFC] Introduce ICFLoopSafetyInfo

This is an alternative implementation of LoopSafetyInfo that uses the implicit
control flow tracking to give precise answers on queries "whether or not this
block contains throwing instructions". This rules out false-positive answers on
LoopSafetyInfo's queries.

This patch only introduces the new implementation. It is not currently used in
any pass. The enabling patches will go separately, through review.

The plan is to completely replace all uses of LoopSafetyInfo with
ICFLoopSafetyInfo in the future, but to avoid introducing functional problems,
we will do it pass by pass.

llvm-svn: 344601

1 files changed, 31 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/MustExecute.cpp b/llvm/lib/Analysis/MustExecute.cpp
index 4e42f336dc7..64ee2a7e5b0 100644
--- a/llvm/lib/Analysis/MustExecute.cpp
+++ b/llvm/lib/Analysis/MustExecute.cpp
@@ -61,6 +61,31 @@ void SimpleLoopSafetyInfo::computeLoopSafetyInfo(const Loop *CurLoop) {
   computeBlockColors(CurLoop);
 }
 
+bool ICFLoopSafetyInfo::blockMayThrow(const BasicBlock *BB) const {
+  return ICF.hasICF(BB);
+}
+
+bool ICFLoopSafetyInfo::anyBlockMayThrow() const {
+  return MayThrow;
+}
+
+void ICFLoopSafetyInfo::computeLoopSafetyInfo(const Loop *CurLoop) {
+  assert(CurLoop != nullptr && "CurLoop can't be null");
+  ICF.clear();
+  MayThrow = false;
+  // Figure out the fact that at least one block may throw.
+  for (auto &BB : CurLoop->blocks())
+    if (ICF.hasICF(&*BB)) {
+      MayThrow = true;
+      break;
+    }
+  computeBlockColors(CurLoop);
+}
+
+void ICFLoopSafetyInfo::dropCachedInfo(const BasicBlock *BB) {
+  ICF.invalidateBlock(BB);
+}
+
 void LoopSafetyInfo::computeBlockColors(const Loop *CurLoop) {
   // Compute funclet colors if we might sink/hoist in a function with a funclet
   // personality routine.
@@ -215,6 +240,12 @@ bool SimpleLoopSafetyInfo::isGuaranteedToExecute(const Instruction &Inst,
   return allLoopPathsLeadToBlock(CurLoop, Inst.getParent(), DT);
 }
 
+bool ICFLoopSafetyInfo::isGuaranteedToExecute(const Instruction &Inst,
+                                              const DominatorTree *DT,
+                                              const Loop *CurLoop) const {
+  return !ICF.isDominatedByICFIFromSameBlock(&Inst) &&
+         allLoopPathsLeadToBlock(CurLoop, Inst.getParent(), DT);
+}
 
 namespace {
   struct MustExecutePrinter : public FunctionPass {