[llvm] 39beeef - [LVI] Don't use dominator tree in isValidAssumeForContext()

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2020-05-17T21:39:35+02:00
New Revision: 39beeeff205caf75ee56ff8967e2b12e7b3fb644

URL: https://github.com/llvm/llvm-project/commit/39beeeff205caf75ee56ff8967e2b12e7b3fb644
DIFF: https://github.com/llvm/llvm-project/commit/39beeeff205caf75ee56ff8967e2b12e7b3fb644.diff

LOG: [LVI] Don't use dominator tree in isValidAssumeForContext()

LVI and its consumers currently have quite a bit of complexity
related to dominator tree management. However, it doesn't look
like it is actually needed...

The only use of the dominator tree is inside isValidAssumeForContext().
However, due to the way LVI queries work, it is not needed:
If we query a value for some block, we will first get the edge values
from all predecessor blocks, which also includes an intersection with
assumptions that apply to the terminator of the predecessor. As such,
we will already have processed all assumptions from predecessor blocks
(this is actually stronger than what isValidAssumeForContext() does
with a DT, because this is capable of combining non-dominating
assumptions). The only additional assumptions we need to take into
account are those in the block being queried. And we don't need a
dominator tree for that.

This patch only removes the use of DT, I will drop the machinery
around it in a followup.

Differential Revision: https://reviews.llvm.org/D76797

Added: 
    

Modified: 
    llvm/lib/Analysis/LazyValueInfo.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index 9dc3f7aa184b..f2809283592d 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -802,11 +802,16 @@ void LazyValueInfoImpl::intersectAssumeOrGuardBlockValueConstantRange(
   if (!BBI)
     return;
 
+  BasicBlock *BB = BBI->getParent();
   for (auto &AssumeVH : AC->assumptionsFor(Val)) {
     if (!AssumeVH)
       continue;
+
+    // Only check assumes in the block of the context instruction. Other
+    // assumes will have already been taken into account when the value was
+    // propagated from predecessor blocks.
     auto *I = cast<CallInst>(AssumeVH);
-    if (!isValidAssumeForContext(I, BBI, DT))
+    if (I->getParent() != BB || !isValidAssumeForContext(I, BBI))
       continue;
 
     BBLV = intersect(BBLV, getValueFromCondition(Val, I->getArgOperand(0)));
@@ -818,10 +823,10 @@ void LazyValueInfoImpl::intersectAssumeOrGuardBlockValueConstantRange(
   if (!GuardDecl || GuardDecl->use_empty())
     return;
 
-  if (BBI->getIterator() == BBI->getParent()->begin())
+  if (BBI->getIterator() == BB->begin())
     return;
   for (Instruction &I : make_range(std::next(BBI->getIterator().getReverse()),
-                                   BBI->getParent()->rend())) {
+                                   BB->rend())) {
     Value *Cond = nullptr;
     if (match(&I, m_Intrinsic<Intrinsic::experimental_guard>(m_Value(Cond))))
       BBLV = intersect(BBLV, getValueFromCondition(Val, Cond));