[InstCombine] Remove redundant @llvm.assume intrinsics

For any @llvm.assume intrinsic, if there is another which dominates it and uses
the same condition, then it is redundant and can be removed. While this does
not alter the semantics of the @llvm.assume intrinsics, it makes subsequent
handling more efficient (and the resulting IR easier to read).

llvm-svn: 219067

1 files changed, 17 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 30fc3c93383..27a64d8bcde 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -16,6 +16,7 @@
 #include "llvm/Analysis/MemoryBuiltins.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/Transforms/Utils/BuildLibCalls.h"
 #include "llvm/Transforms/Utils/Local.h"
@@ -1016,6 +1017,22 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
                           II->getName());
       return EraseInstFromFunction(*II);
     }
+
+    // If there is a dominating assume with the same condition as this one,
+    // then this one is redundant, and should be removed.
+    if (DT) {
+      for (User *U : IIOperand->users()) {
+        Instruction *User = dyn_cast<Instruction>(U);
+        if (!User || User == II)
+          continue;
+
+        if (match(User,
+                  m_Intrinsic<Intrinsic::assume>(m_Specific(IIOperand))) &&
+            DT->dominates(User, II))
+          return EraseInstFromFunction(*II);
+      }
+    }
+
     break;
   }
   }