[llvm] r267620 - [LVI] Apply transfer rule for overdefine inputs for binary operators

[Philip Reames via llvm-commits]

Author: reames
Date: Tue Apr 26 18:10:35 2016
New Revision: 267620

URL: http://llvm.org/viewvc/llvm-project?rev=267620&view=rev
Log:
[LVI] Apply transfer rule for overdefine inputs for binary operators

As pointed out by John Regehr over in http://reviews.llvm.org/D19485, LVI was being incredibly stupid about applying its transfer rules.  Rather than gathering local facts from the expression itself, it was simply giving up entirely if one of the inputs was overdefined.  This greatly impacts the precision of the overall analysis and makes it far more fragile as well.

This patch builds on 267609 which did the same thing for unary casts.


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

Modified: llvm/trunk/lib/Analysis/LazyValueInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/LazyValueInfo.cpp?rev=267620&r1=267619&r2=267620&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/LazyValueInfo.cpp (original)
+++ llvm/trunk/lib/Analysis/LazyValueInfo.cpp Tue Apr 26 18:10:35 2016
@@ -1063,22 +1063,27 @@ bool LazyValueInfoCache::solveBlockValue
 bool LazyValueInfoCache::solveBlockValueBinaryOp(LVILatticeVal &BBLV,
                                                  Instruction *BBI,
                                                  BasicBlock *BB) {
+
+  assert(BBI->getOperand(0)->getType()->isSized() &&
+         "all operands to binary operators are sized");
   
-  // Figure out the range of the LHS.  If that fails, bail.
-  if (!hasBlockValue(BBI->getOperand(0), BB)) {
+  // Figure out the range of the LHS.  If that fails, use a conservative range,
+  // but apply the transfer rule anyways.  This lets us pick up facts from
+  // expressions like "and i32 (call i32 @foo()), 32"
+  if (!hasBlockValue(BBI->getOperand(0), BB))
     if (pushBlockValue(std::make_pair(BB, BBI->getOperand(0))))
+      // More work to do before applying this transfer rule.
       return false;
-    BBLV.markOverdefined();
-    return true;
-  }
 
-  LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
-  intersectAssumeBlockValueConstantRange(BBI->getOperand(0), LHSVal, BBI);
-  if (!LHSVal.isConstantRange()) {
-    BBLV.markOverdefined();
-    return true;
+  const unsigned OperandBitWidth =
+    DL.getTypeSizeInBits(BBI->getOperand(0)->getType());
+  ConstantRange LHSRange = ConstantRange(OperandBitWidth);
+  if (hasBlockValue(BBI->getOperand(0), BB)) {
+    LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
+    intersectAssumeBlockValueConstantRange(BBI->getOperand(0), LHSVal, BBI);
+    if (LHSVal.isConstantRange())
+      LHSRange = LHSVal.getConstantRange();
   }
-  ConstantRange LHSRange = LHSVal.getConstantRange();
 
   ConstantInt *RHS = cast<ConstantInt>(BBI->getOperand(1));
   ConstantRange RHSRange = ConstantRange(RHS->getValue());

Modified: llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll?rev=267620&r1=267619&r2=267620&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll (original)
+++ llvm/trunk/test/Transforms/CorrelatedValuePropagation/basic.ll Tue Apr 26 18:10:35 2016
@@ -440,3 +440,26 @@ entry:
 exit:
   ret i1 %cmp
 }
+
+
+define i1 @and_unknown(i32 %a) {
+; CHECK-LABEL: @and_unknown
+; CHECK: ret i1 true
+entry:
+  %and = and i32 %a, 128
+  %cmp = icmp sle i32 %and, 128
+  br label %exit
+exit:
+  ret i1 %cmp
+}
+
+define i1 @lshr_unknown(i32 %a) {
+; CHECK-LABEL: @lshr_unknown
+; CHECK: ret i1 true
+entry:
+  %and = lshr i32 %a, 30
+  %cmp = icmp sle i32 %and, 128
+  br label %exit
+exit:
+  ret i1 %cmp
+}