[llvm] db9d00c - [LVI] Handle mask not equal zero conditions

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2021-05-01T23:08:49+02:00
New Revision: db9d00c5e7b02b5fe77cb8f3c7c40405c5f1222a

URL: https://github.com/llvm/llvm-project/commit/db9d00c5e7b02b5fe77cb8f3c7c40405c5f1222a
DIFF: https://github.com/llvm/llvm-project/commit/db9d00c5e7b02b5fe77cb8f3c7c40405c5f1222a.diff

LOG: [LVI] Handle mask not equal zero conditions

If V & Mask != 0, we know that at least one of the bits in Mask
must be set, so the value must be >= the lowest bit in Mask.

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index 24631d7da2fe..104f0e4b785d 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -1103,17 +1103,27 @@ static ValueLatticeElement getValueFromICmpCondition(Value *Val, ICmpInst *ICI,
   if (matchICmpOperand(Offset, RHS, Val, SwappedPred))
     return getValueFromSimpleICmpCondition(SwappedPred, LHS, Offset);
 
-  // If (Val & Mask) == C then all the masked bits are known and we can compute
-  // a value range based on that.
   const APInt *Mask, *C;
-  if (EdgePred == ICmpInst::ICMP_EQ &&
-      match(LHS, m_And(m_Specific(Val), m_APInt(Mask))) &&
+  if (match(LHS, m_And(m_Specific(Val), m_APInt(Mask))) &&
       match(RHS, m_APInt(C))) {
-    KnownBits Known;
-    Known.Zero = ~*C & *Mask;
-    Known.One = *C & *Mask;
-    return ValueLatticeElement::getRange(
-        ConstantRange::fromKnownBits(Known, /*IsSigned*/ false));
+    // If (Val & Mask) == C then all the masked bits are known and we can
+    // compute a value range based on that.
+    if (EdgePred == ICmpInst::ICMP_EQ) {
+      KnownBits Known;
+      Known.Zero = ~*C & *Mask;
+      Known.One = *C & *Mask;
+      return ValueLatticeElement::getRange(
+          ConstantRange::fromKnownBits(Known, /*IsSigned*/ false));
+    }
+    // If (Val & Mask) != 0 then the value must be larger than the lowest set
+    // bit of Mask.
+    if (EdgePred == ICmpInst::ICMP_NE && !Mask->isNullValue() &&
+        C->isNullValue()) {
+      unsigned BitWidth = Ty->getIntegerBitWidth();
+      return ValueLatticeElement::getRange(ConstantRange::getNonEmpty(
+          APInt::getOneBitSet(BitWidth, Mask->countTrailingZeros()),
+          APInt::getNullValue(BitWidth)));
+    }
   }
 
   return ValueLatticeElement::getOverdefined();

diff  --git a/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll b/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
index 141632cbcab5..c195dc10dc6b 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
@@ -1090,8 +1090,7 @@ define void @test_icmp_mask_ne(i32 %a) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i32 [[AND]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
 ; CHECK:       if.true:
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp uge i32 [[A]], 2
-; CHECK-NEXT:    call void @check1(i1 [[CMP2]])
+; CHECK-NEXT:    call void @check1(i1 true)
 ; CHECK-NEXT:    [[CMP3:%.*]] = icmp ugt i32 [[A]], 2
 ; CHECK-NEXT:    call void @check1(i1 [[CMP3]])
 ; CHECK-NEXT:    [[CMP4:%.*]] = icmp ult i32 [[A]], -1