[InstCombine] Allow InstCombine to merge adjacent guards

Summary:
If there are two adjacent guards with different conditions, we can
remove one of them and include its condition into the condition of
another one. This patch allows InstCombine to merge them by the
following pattern:

    guard(a); guard(b) -> guard(a & b).

Reviewers: reames, apilipenko, igor-laevsky, anna, sanjoy

Reviewed By: sanjoy

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D29378

llvm-svn: 293778

1 files changed, 14 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 56983dc6036..f088671c6d7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3255,16 +3255,24 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
   }
 
   case Intrinsic::experimental_guard: {
-    Value *IIOperand = II->getArgOperand(0);
+    // Is this guard followed by another guard?
+    Instruction *NextInst = II->getNextNode();
+    Value *NextCond = nullptr;
+    if (match(NextInst,
+              m_Intrinsic<Intrinsic::experimental_guard>(m_Value(NextCond)))) {
+      Value *CurrCond = II->getArgOperand(0);
 
-    // Remove a guard if it is immediately followed by an identical guard.
-    if (match(II->getNextNode(),
-              m_Intrinsic<Intrinsic::experimental_guard>(m_Specific(IIOperand))))
-      return eraseInstFromFunction(*II);
+      // Remove a guard that it is immediately preceeded by an identical guard.
+      if (CurrCond == NextCond)
+        return eraseInstFromFunction(*NextInst);
+
+      // Otherwise canonicalize guard(a); guard(b) -> guard(a & b).
+      II->setArgOperand(0, Builder->CreateAnd(CurrCond, NextCond));
+      return eraseInstFromFunction(*NextInst);
+    }
     break;
   }
   }
-
   return visitCallSite(II);
 }