[llvm] 445db89 - [LVI] Get value range from mask comparison

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2020-09-20T21:13:57+02:00
New Revision: 445db89b537e5397a2d4b08e79751edb845b2c2a

URL: https://github.com/llvm/llvm-project/commit/445db89b537e5397a2d4b08e79751edb845b2c2a
DIFF: https://github.com/llvm/llvm-project/commit/445db89b537e5397a2d4b08e79751edb845b2c2a.diff

LOG: [LVI] Get value range from mask comparison

InstCombine likes to canonicalize comparisons of the form
X == C || X == C+1 into (X & -2) == C'. Make sure LVI can still
recover the value range from this. Can of course also be useful
for proper mask comparisons.

For the sake of clarity, the implementation goes through KnownBits
to compute the range.

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 4e9505a12cb8..cc364fc93337 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -36,6 +36,7 @@
 #include "llvm/InitializePasses.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/FormattedStream.h"
+#include "llvm/Support/KnownBits.h"
 #include "llvm/Support/raw_ostream.h"
 #include <map>
 using namespace llvm;
@@ -1145,6 +1146,19 @@ 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))) &&
+      match(RHS, m_APInt(C))) {
+    KnownBits Known;
+    Known.Zero = ~*C & *Mask;
+    Known.One = *C & *Mask;
+    return ValueLatticeElement::getRange(
+        ConstantRange::fromKnownBits(Known, /*IsSigned*/ false));
+  }
+
   return ValueLatticeElement::getOverdefined();
 }
 

diff  --git a/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll b/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
index 76d8e0d00f70..cdc5140b6548 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll
@@ -995,14 +995,10 @@ define void @test_icmp_mask_two_values(i32 %a) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[AND]], 10
 ; CHECK-NEXT:    br i1 [[CMP]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
 ; CHECK:       if.true:
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp uge i32 [[A]], 10
-; CHECK-NEXT:    call void @check1(i1 [[CMP2]])
-; CHECK-NEXT:    [[CMP3:%.*]] = icmp ule i32 [[A]], 11
-; CHECK-NEXT:    call void @check1(i1 [[CMP3]])
-; CHECK-NEXT:    [[CMP4:%.*]] = icmp ult i32 [[A]], 10
-; CHECK-NEXT:    call void @check1(i1 [[CMP4]])
-; CHECK-NEXT:    [[CMP5:%.*]] = icmp ugt i32 [[A]], 11
-; CHECK-NEXT:    call void @check1(i1 [[CMP5]])
+; CHECK-NEXT:    call void @check1(i1 true)
+; CHECK-NEXT:    call void @check1(i1 true)
+; CHECK-NEXT:    call void @check1(i1 false)
+; CHECK-NEXT:    call void @check1(i1 false)
 ; CHECK-NEXT:    ret void
 ; CHECK:       if.false:
 ; CHECK-NEXT:    ret void
@@ -1032,8 +1028,7 @@ define void @test_icmp_mask_bit_set(i32 %a) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[AND]], 32
 ; CHECK-NEXT:    br i1 [[CMP]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
 ; CHECK:       if.true:
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp uge i32 [[A]], 32
-; CHECK-NEXT:    call void @check1(i1 [[CMP2]])
+; CHECK-NEXT:    call void @check1(i1 true)
 ; CHECK-NEXT:    [[CMP3:%.*]] = icmp uge i32 [[A]], 33
 ; CHECK-NEXT:    call void @check1(i1 [[CMP3]])
 ; CHECK-NEXT:    ret void
@@ -1061,8 +1056,7 @@ define void @test_icmp_mask_bit_unset(i32 %a) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[AND]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
 ; CHECK:       if.true:
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp ule i32 [[A]], -33
-; CHECK-NEXT:    call void @check1(i1 [[CMP2]])
+; CHECK-NEXT:    call void @check1(i1 true)
 ; CHECK-NEXT:    [[CMP3:%.*]] = icmp ule i32 [[A]], -34
 ; CHECK-NEXT:    call void @check1(i1 [[CMP3]])
 ; CHECK-NEXT:    ret void