[EarlyCSE] Mark the condition of assume intrinsic as true

EarlyCSE should not just ignore assumes. It should use the fact that its condition is true for all dominated instructions.

Reviewers: sanjoy, reames, apilipenko, anna, skatkov

Reviewed By: reames, sanjoy

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32482

llvm-svn: 301625

1 files changed, 9 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
index da33c7aa836..def10f1d41b 100644
--- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -635,10 +635,16 @@ bool EarlyCSE::processNode(DomTreeNode *Node) {
 
     // Skip assume intrinsics, they don't really have side effects (although
     // they're marked as such to ensure preservation of control dependencies),
-    // and this pass will not disturb any of the assumption's control
-    // dependencies.
+    // and this pass will not bother with its removal. However, we should mark
+    // its condition as true for all dominated blocks.
     if (match(Inst, m_Intrinsic<Intrinsic::assume>())) {
-      DEBUG(dbgs() << "EarlyCSE skipping assumption: " << *Inst << '\n');
+      auto *CondI =
+          dyn_cast<Instruction>(cast<CallInst>(Inst)->getArgOperand(0));
+      if (CondI && SimpleValue::canHandle(CondI)) {
+        DEBUG(dbgs() << "EarlyCSE considering assumption: " << *Inst << '\n');
+        AvailableValues.insert(CondI, ConstantInt::getTrue(BB->getContext()));
+      } else
+        DEBUG(dbgs() << "EarlyCSE skipping assumption: " << *Inst << '\n');
       continue;
     }