[NFC] Factor out utilities for manipulating widenable branches

With the widenable condition construct, we have the ability to reason about branches which can be 'widened' (i.e. made to fail more often).  We've got a couple o transforms which leverage this.  This patch just cleans up the API a bit.

This is prep work for generalizing our definition of a widenable branch slightly.  At the moment "br i1 (and A, wc()), ..." is considered widenable, but oddly, neither "br i1 (and wc(), B), ..." or "br i1 wc(), ..." is.  That clearly needs addressed, so first, let's centralize the code in one place.

6 files changed, 53 insertions, 13 deletions

diff --git a/llvm/include/llvm/Analysis/GuardUtils.h b/llvm/include/llvm/Analysis/GuardUtils.h
index 41e7b7c..f4492c7 100644
--- a/llvm/include/llvm/Analysis/GuardUtils.h
+++ b/llvm/include/llvm/Analysis/GuardUtils.h
@@ -22,6 +22,10 @@ class Value;
 /// of llvm.experimental.guard intrinsic.
 bool isGuard(const User *U);
 
+/// Returns true iff \p U is a widenable branch (that is, parseWidenableBranch
+/// returns true).
+bool isWidenableBranch(const User *U);
+
 /// Returns true iff \p U has semantics of a guard expressed in a form of a
 /// widenable conditional branch to deopt block.
 bool isGuardAsWidenableBranch(const User *U);
diff --git a/llvm/include/llvm/Transforms/Utils/GuardUtils.h b/llvm/include/llvm/Transforms/Utils/GuardUtils.h
index 3b365c5..43cd267 100644
--- a/llvm/include/llvm/Transforms/Utils/GuardUtils.h
+++ b/llvm/include/llvm/Transforms/Utils/GuardUtils.h
@@ -14,8 +14,10 @@
 
 namespace llvm {
 
+class BranchInst;
 class CallInst;
 class Function;
+class Value;
 
 /// Splits control flow at point of \p Guard, replacing it with explicit branch
 /// by the condition of guard's first argument. The taken branch then goes to
@@ -24,6 +26,16 @@ class Function;
 /// deoptimize function \p DeoptIntrinsic.
 void makeGuardControlFlowExplicit(Function *DeoptIntrinsic, CallInst *Guard);
 
+/// Given a branch we know is widenable (defined per Analysis/GuardUtils.h),
+/// widen it such that condition 'NewCond' is also known to hold on the taken
+/// path.  Branch remains widenable after transform.
+void widenWidenableBranch(BranchInst *WidenableBR, Value *NewCond);
+
+/// Given a branch we know is widenable (defined per Analysis/GuardUtils.h),
+/// *set* it's condition such that (only) 'Cond' is known to hold on the taken
+/// path and that the branch remains widenable after transform.
+void setWidenableBranchCond(BranchInst *WidenableBR, Value *Cond);
+
 } // llvm
 
 #endif // LLVM_TRANSFORMS_UTILS_GUARDUTILS_H
diff --git a/llvm/lib/Analysis/GuardUtils.cpp b/llvm/lib/Analysis/GuardUtils.cpp
index 863443c..6dc2b74 100644
--- a/llvm/lib/Analysis/GuardUtils.cpp
+++ b/llvm/lib/Analysis/GuardUtils.cpp
@@ -19,6 +19,13 @@ bool llvm::isGuard(const User *U) {
   return match(U, m_Intrinsic<Intrinsic::experimental_guard>());
 }
 
+bool llvm::isWidenableBranch(const User *U) {
+  Value *Condition, *WidenableCondition;
+  BasicBlock *GuardedBB, *DeoptBB;
+  return parseWidenableBranch(U, Condition, WidenableCondition, GuardedBB,
+                              DeoptBB);
+}
+
 bool llvm::isGuardAsWidenableBranch(const User *U) {
   Value *Condition, *WidenableCondition;
   BasicBlock *GuardedBB, *DeoptBB;
diff --git a/llvm/lib/Transforms/Scalar/GuardWidening.cpp b/llvm/lib/Transforms/Scalar/GuardWidening.cpp
index 27439a2..943cc9a 100644
--- a/llvm/lib/Transforms/Scalar/GuardWidening.cpp
+++ b/llvm/lib/Transforms/Scalar/GuardWidening.cpp
@@ -58,6 +58,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/KnownBits.h"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/GuardUtils.h"
 #include "llvm/Transforms/Utils/LoopUtils.h"
 #include <functional>
 
@@ -277,11 +278,7 @@ class GuardWideningImpl {
     widenCondCommon(getCondition(ToWiden), NewCondition, ToWiden, Result,
                     InvertCondition);
     if (isGuardAsWidenableBranch(ToWiden)) {
-      auto *BI = cast<BranchInst>(ToWiden);
-      auto *And = cast<Instruction>(BI->getCondition());
-      And->setOperand(0, Result);
-      And->moveBefore(ToWiden);
-      assert(isGuardAsWidenableBranch(ToWiden) && "still widenable?");
+      setWidenableBranchCond(cast<BranchInst>(ToWiden), Result);
       return;
     }
     setCondition(ToWiden, Result);
diff --git a/llvm/lib/Transforms/Scalar/LoopPredication.cpp b/llvm/lib/Transforms/Scalar/LoopPredication.cpp
index 9d67046..1962c8b 100644
--- a/llvm/lib/Transforms/Scalar/LoopPredication.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopPredication.cpp
@@ -196,6 +196,7 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/GuardUtils.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/LoopUtils.h"
 
@@ -1144,14 +1145,7 @@ bool LoopPredication::predicateLoopExits(Loop *L, SCEVExpander &Rewriter) {
     // context.
     NewCond = B.CreateFreeze(NewCond);
 
-    Value *Cond, *WC;
-    BasicBlock *IfTrueBB, *IfFalseBB;
-    bool Success =
-        parseWidenableBranch(WidenableBR, Cond, WC, IfTrueBB, IfFalseBB);
-    assert(Success && "implied from above");
-    (void)Success;
-    Instruction *WCAnd = cast<Instruction>(WidenableBR->getCondition());
-    WCAnd->setOperand(0, B.CreateAnd(NewCond, Cond));
+    widenWidenableBranch(WidenableBR, NewCond);
 
     Value *OldCond = BI->getCondition();
     BI->setCondition(ConstantInt::get(OldCond->getType(), !ExitIfTrue));
diff --git a/llvm/lib/Transforms/Utils/GuardUtils.cpp b/llvm/lib/Transforms/Utils/GuardUtils.cpp
index 8069aba..37fca0d 100644
--- a/llvm/lib/Transforms/Utils/GuardUtils.cpp
+++ b/llvm/lib/Transforms/Utils/GuardUtils.cpp
@@ -10,6 +10,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Utils/GuardUtils.h"
+#include "llvm/Analysis/GuardUtils.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instructions.h"
@@ -62,3 +63,28 @@ void llvm::makeGuardControlFlowExplicit(Function *DeoptIntrinsic,
   DeoptCall->setCallingConv(Guard->getCallingConv());
   DeoptBlockTerm->eraseFromParent();
 }
+
+
+void llvm::widenWidenableBranch(BranchInst *WidenableBR, Value *NewCond) {
+  assert(isWidenableBranch(WidenableBR) && "precondition");
+
+  Instruction *WCAnd = cast<Instruction>(WidenableBR->getCondition());
+  // Condition is only guaranteed to dominate branch
+  WCAnd->moveBefore(WidenableBR);
+  Value *OldCond = WCAnd->getOperand(0);
+  IRBuilder<> B(WCAnd);
+  WCAnd->setOperand(0, B.CreateAnd(NewCond, OldCond));
+
+  assert(isWidenableBranch(WidenableBR) && "preserve widenabiliy");
+}
+
+void llvm::setWidenableBranchCond(BranchInst *WidenableBR, Value *NewCond) {
+  assert(isWidenableBranch(WidenableBR) && "precondition");
+
+  Instruction *WCAnd = cast<Instruction>(WidenableBR->getCondition());
+  // Condition is only guaranteed to dominate branch
+  WCAnd->moveBefore(WidenableBR);
+  WCAnd->setOperand(0, NewCond);
+
+  assert(isWidenableBranch(WidenableBR) && "preserve widenabiliy");
+}