[llvm] 14e540f - [LVI] Handle unions of conditions

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2021-01-01T16:46:21+01:00
New Revision: 14e540febcdace3b650dba2b8bb0e770b90409ad

URL: https://github.com/llvm/llvm-project/commit/14e540febcdace3b650dba2b8bb0e770b90409ad
DIFF: https://github.com/llvm/llvm-project/commit/14e540febcdace3b650dba2b8bb0e770b90409ad.diff

LOG: [LVI] Handle unions of conditions

LVI previously handled "if (L && R)" conditions, but not
"if (L || R)" conditions. The latter case can still produce
useful information if L and R both constrain the same variable.

This adds support for handling the "if (L || R)" case as well.
The only difference is that we take the union instead of the
intersection of the lattice values.

Added: 
    

Modified: 
    llvm/lib/Analysis/LazyValueInfo.cpp
    llvm/test/Transforms/CorrelatedValuePropagation/basic.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index d95c9064f570..ba2b6fe94c18 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -1201,13 +1201,13 @@ getValueFromConditionImpl(Value *Val, Value *Cond, bool isTrueDest,
       if (EVI->getNumIndices() == 1 && *EVI->idx_begin() == 1)
         return getValueFromOverflowCondition(Val, WO, isTrueDest);
 
-  // Handle conditions in the form of (cond1 && cond2), we know that on the
-  // true dest path both of the conditions hold. Similarly for conditions of
-  // the form (cond1 || cond2), we know that on the false dest path neither
-  // condition holds.
   Value *L, *R;
-  if (isTrueDest ? !match(Cond, m_LogicalAnd(m_Value(L), m_Value(R)))
-                 : !match(Cond, m_LogicalOr(m_Value(L), m_Value(R))))
+  bool IsAnd;
+  if (match(Cond, m_LogicalAnd(m_Value(L), m_Value(R))))
+    IsAnd = true;
+  else if (match(Cond, m_LogicalOr(m_Value(L), m_Value(R))))
+    IsAnd = false;
+  else
     return ValueLatticeElement::getOverdefined();
 
   // Prevent infinite recursion if Cond references itself as in this example:
@@ -1217,6 +1217,18 @@ getValueFromConditionImpl(Value *Val, Value *Cond, bool isTrueDest,
   if (L == Cond || R == Cond)
     return ValueLatticeElement::getOverdefined();
 
+  // if (L && R) -> intersect L and R
+  // if (!(L || R)) -> intersect L and R
+  // if (L || R) -> union L and R
+  // if (!(L && R)) -> union L and R
+  if (isTrueDest ^ IsAnd) {
+    ValueLatticeElement V = getValueFromCondition(Val, L, isTrueDest, Visited);
+    if (V.isOverdefined())
+      return V;
+    V.mergeIn(getValueFromCondition(Val, R, isTrueDest, Visited));
+    return V;
+  }
+
   return intersect(getValueFromCondition(Val, L, isTrueDest, Visited),
                    getValueFromCondition(Val, R, isTrueDest, Visited));
 }

diff  --git a/llvm/test/Transforms/CorrelatedValuePropagation/basic.ll b/llvm/test/Transforms/CorrelatedValuePropagation/basic.ll
index f04a20b6abae..d8ecbbfcb920 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/basic.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/basic.ll
@@ -1262,16 +1262,14 @@ define void @or_union(i32 %a, i1* %p) {
 ; CHECK-NEXT:    [[OR:%.*]] = or i1 [[CMP1]], [[CMP2]]
 ; CHECK-NEXT:    br i1 [[OR]], label [[GUARD:%.*]], label [[EXIT:%.*]]
 ; CHECK:       guard:
-; CHECK-NEXT:    [[C1:%.*]] = icmp eq i32 [[A]], 9
-; CHECK-NEXT:    store i1 [[C1]], i1* [[P:%.*]], align 1
+; CHECK-NEXT:    store i1 false, i1* [[P:%.*]], align 1
 ; CHECK-NEXT:    [[C2:%.*]] = icmp eq i32 [[A]], 10
 ; CHECK-NEXT:    store i1 [[C2]], i1* [[P]], align 1
 ; CHECK-NEXT:    [[C3:%.*]] = icmp eq i32 [[A]], 11
 ; CHECK-NEXT:    store i1 [[C3]], i1* [[P]], align 1
 ; CHECK-NEXT:    [[C4:%.*]] = icmp eq i32 [[A]], 12
 ; CHECK-NEXT:    store i1 [[C4]], i1* [[P]], align 1
-; CHECK-NEXT:    [[C5:%.*]] = icmp eq i32 [[A]], 13
-; CHECK-NEXT:    store i1 [[C5]], i1* [[P]], align 1
+; CHECK-NEXT:    store i1 false, i1* [[P]], align 1
 ; CHECK-NEXT:    br label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
@@ -1328,16 +1326,14 @@ define void @and_union(i32 %a, i1* %p) {
 ; CHECK-NEXT:    [[AND:%.*]] = and i1 [[CMP1]], [[CMP2]]
 ; CHECK-NEXT:    br i1 [[AND]], label [[EXIT:%.*]], label [[GUARD:%.*]]
 ; CHECK:       guard:
-; CHECK-NEXT:    [[C1:%.*]] = icmp eq i32 [[A]], 9
-; CHECK-NEXT:    store i1 [[C1]], i1* [[P:%.*]], align 1
+; CHECK-NEXT:    store i1 false, i1* [[P:%.*]], align 1
 ; CHECK-NEXT:    [[C2:%.*]] = icmp eq i32 [[A]], 10
 ; CHECK-NEXT:    store i1 [[C2]], i1* [[P]], align 1
 ; CHECK-NEXT:    [[C3:%.*]] = icmp eq i32 [[A]], 11
 ; CHECK-NEXT:    store i1 [[C3]], i1* [[P]], align 1
 ; CHECK-NEXT:    [[C4:%.*]] = icmp eq i32 [[A]], 12
 ; CHECK-NEXT:    store i1 [[C4]], i1* [[P]], align 1
-; CHECK-NEXT:    [[C5:%.*]] = icmp eq i32 [[A]], 13
-; CHECK-NEXT:    store i1 [[C5]], i1* [[P]], align 1
+; CHECK-NEXT:    store i1 false, i1* [[P]], align 1
 ; CHECK-NEXT:    br label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void