Make use of @llvm.assume in ValueTracking (computeKnownBits, etc.)

This change, which allows @llvm.assume to be used from within computeKnownBits
(and other associated functions in ValueTracking), adds some (optional)
parameters to computeKnownBits and friends. These functions now (optionally)
take a "context" instruction pointer, an AssumptionTracker pointer, and also a
DomTree pointer, and most of the changes are just to pass this new information
when it is easily available from InstSimplify, InstCombine, etc.

As explained below, the significant conceptual change is that known properties
of a value might depend on the control-flow location of the use (because we
care that the @llvm.assume dominates the use because assumptions have
control-flow dependencies). This means that, when we ask if bits are known in a
value, we might get different answers for different uses.

The significant changes are all in ValueTracking. Two main changes: First, as
with the rest of the code, new parameters need to be passed around. To make
this easier, I grouped them into a structure, and I made internal static
versions of the relevant functions that take this structure as a parameter. The
new code does as you might expect, it looks for @llvm.assume calls that make
use of the value we're trying to learn something about (often indirectly),
attempts to pattern match that expression, and uses the result if successful.
By making use of the AssumptionTracker, the process of finding @llvm.assume
calls is not expensive.

Part of the structure being passed around inside ValueTracking is a set of
already-considered @llvm.assume calls. This is to prevent a query using, for
example, the assume(a == b), to recurse on itself. The context and DT params
are used to find applicable assumptions. An assumption needs to dominate the
context instruction, or come after it deterministically. In this latter case we
only handle the specific case where both the assumption and the context
instruction are in the same block, and we need to exclude assumptions from
being used to simplify their own ephemeral values (those which contribute only
to the assumption) because otherwise the assumption would prove its feeding
comparison trivial and would be removed.

This commit adds the plumbing and the logic for a simple masked-bit propagation
(just enough to write a regression test). Future commits add more patterns
(and, correspondingly, more regression tests).

llvm-svn: 217342

1 files changed, 29 insertions, 21 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index ed6253532e0..0a9bb2d1087 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -355,7 +355,7 @@ Value *InstCombiner::FoldLogicalPlusAnd(Value *LHS, Value *RHS,
       if (isRunOfOnes(Mask, MB, ME)) {  // begin/end bit of run, inclusive
         uint32_t BitWidth = cast<IntegerType>(RHS->getType())->getBitWidth();
         APInt Mask(APInt::getLowBitsSet(BitWidth, MB-1));
-        if (MaskedValueIsZero(RHS, Mask))
+        if (MaskedValueIsZero(RHS, Mask, 0, &I))
           break;
       }
     }
@@ -1108,7 +1108,7 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
   if (Value *V = SimplifyVectorOp(I))
     return ReplaceInstUsesWith(I, V);
 
-  if (Value *V = SimplifyAndInst(Op0, Op1, DL))
+  if (Value *V = SimplifyAndInst(Op0, Op1, DL, TLI, DT, AT))
     return ReplaceInstUsesWith(I, V);
 
   // (A|B)&(A|C) -> A|(B&C) etc
@@ -1135,14 +1135,14 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
         if (!Op0I->hasOneUse()) break;
 
         APInt NotAndRHS(~AndRHSMask);
-        if (MaskedValueIsZero(Op0LHS, NotAndRHS)) {
+        if (MaskedValueIsZero(Op0LHS, NotAndRHS, 0, &I)) {
           // Not masking anything out for the LHS, move to RHS.
           Value *NewRHS = Builder->CreateAnd(Op0RHS, AndRHS,
                                              Op0RHS->getName()+".masked");
           return BinaryOperator::Create(Op0I->getOpcode(), Op0LHS, NewRHS);
         }
         if (!isa<Constant>(Op0RHS) &&
-            MaskedValueIsZero(Op0RHS, NotAndRHS)) {
+            MaskedValueIsZero(Op0RHS, NotAndRHS, 0, &I)) {
           // Not masking anything out for the RHS, move to LHS.
           Value *NewLHS = Builder->CreateAnd(Op0LHS, AndRHS,
                                              Op0LHS->getName()+".masked");
@@ -1175,7 +1175,7 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
           uint32_t Zeros = AndRHSMask.countLeadingZeros();
           APInt Mask = APInt::getLowBitsSet(BitWidth, BitWidth - Zeros);
 
-          if (MaskedValueIsZero(Op0LHS, Mask)) {
+          if (MaskedValueIsZero(Op0LHS, Mask, 0, &I)) {
             Value *NewNeg = Builder->CreateNeg(Op0RHS);
             return BinaryOperator::CreateAnd(NewNeg, AndRHS);
           }
@@ -1584,7 +1584,8 @@ static Instruction *MatchSelectFromAndOr(Value *A, Value *B,
 }
 
 /// FoldOrOfICmps - Fold (icmp)|(icmp) if possible.
-Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
+Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS,
+                                   Instruction *CxtI) {
   ICmpInst::Predicate LHSCC = LHS->getPredicate(), RHSCC = RHS->getPredicate();
 
   // Fold (iszero(A & K1) | iszero(A & K2)) ->  (A & (K1 | K2)) != (K1 | K2)
@@ -1604,13 +1605,15 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
       Value *Mask = nullptr;
       Value *Masked = nullptr;
       if (LAnd->getOperand(0) == RAnd->getOperand(0) &&
-          isKnownToBeAPowerOfTwo(LAnd->getOperand(1)) &&
-          isKnownToBeAPowerOfTwo(RAnd->getOperand(1))) {
+          isKnownToBeAPowerOfTwo(LAnd->getOperand(1), false, 0, AT, CxtI, DT) &&
+          isKnownToBeAPowerOfTwo(RAnd->getOperand(1), false, 0, AT, CxtI, DT)) {
         Mask = Builder->CreateOr(LAnd->getOperand(1), RAnd->getOperand(1));
         Masked = Builder->CreateAnd(LAnd->getOperand(0), Mask);
       } else if (LAnd->getOperand(1) == RAnd->getOperand(1) &&
-                 isKnownToBeAPowerOfTwo(LAnd->getOperand(0)) &&
-                 isKnownToBeAPowerOfTwo(RAnd->getOperand(0))) {
+                 isKnownToBeAPowerOfTwo(LAnd->getOperand(0),
+                                        false, 0, AT, CxtI, DT) &&
+                 isKnownToBeAPowerOfTwo(RAnd->getOperand(0),
+                                        false, 0, AT, CxtI, DT)) {
         Mask = Builder->CreateOr(LAnd->getOperand(0), RAnd->getOperand(0));
         Masked = Builder->CreateAnd(LAnd->getOperand(1), Mask);
       }
@@ -2030,7 +2033,7 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
   if (Value *V = SimplifyVectorOp(I))
     return ReplaceInstUsesWith(I, V);
 
-  if (Value *V = SimplifyOrInst(Op0, Op1, DL))
+  if (Value *V = SimplifyOrInst(Op0, Op1, DL, TLI, DT, AT))
     return ReplaceInstUsesWith(I, V);
 
   // (A&B)|(A&C) -> A&(B|C) etc
@@ -2090,7 +2093,7 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
   // (X^C)|Y -> (X|Y)^C iff Y&C == 0
   if (Op0->hasOneUse() &&
       match(Op0, m_Xor(m_Value(A), m_ConstantInt(C1))) &&
-      MaskedValueIsZero(Op1, C1->getValue())) {
+      MaskedValueIsZero(Op1, C1->getValue(), 0, &I)) {
     Value *NOr = Builder->CreateOr(A, Op1);
     NOr->takeName(Op0);
     return BinaryOperator::CreateXor(NOr, C1);
@@ -2099,7 +2102,7 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
   // Y|(X^C) -> (X|Y)^C iff Y&C == 0
   if (Op1->hasOneUse() &&
       match(Op1, m_Xor(m_Value(A), m_ConstantInt(C1))) &&
-      MaskedValueIsZero(Op0, C1->getValue())) {
+      MaskedValueIsZero(Op0, C1->getValue(), 0, &I)) {
     Value *NOr = Builder->CreateOr(A, Op0);
     NOr->takeName(Op0);
     return BinaryOperator::CreateXor(NOr, C1);
@@ -2137,14 +2140,18 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
         // ((V | N) & C1) | (V & C2) --> (V|N) & (C1|C2)
         // iff (C1&C2) == 0 and (N&~C1) == 0
         if (match(A, m_Or(m_Value(V1), m_Value(V2))) &&
-            ((V1 == B && MaskedValueIsZero(V2, ~C1->getValue())) ||  // (V|N)
-             (V2 == B && MaskedValueIsZero(V1, ~C1->getValue()))))   // (N|V)
+            ((V1 == B &&
+              MaskedValueIsZero(V2, ~C1->getValue(), 0, &I)) || // (V|N)
+             (V2 == B &&
+              MaskedValueIsZero(V1, ~C1->getValue(), 0, &I))))  // (N|V)
           return BinaryOperator::CreateAnd(A,
                                 Builder->getInt(C1->getValue()|C2->getValue()));
         // Or commutes, try both ways.
         if (match(B, m_Or(m_Value(V1), m_Value(V2))) &&
-            ((V1 == A && MaskedValueIsZero(V2, ~C2->getValue())) ||  // (V|N)
-             (V2 == A && MaskedValueIsZero(V1, ~C2->getValue()))))   // (N|V)
+            ((V1 == A &&
+              MaskedValueIsZero(V2, ~C2->getValue(), 0, &I)) || // (V|N)
+             (V2 == A &&
+              MaskedValueIsZero(V1, ~C2->getValue(), 0, &I))))  // (N|V)
           return BinaryOperator::CreateAnd(B,
                                 Builder->getInt(C1->getValue()|C2->getValue()));
 
@@ -2300,7 +2307,7 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
 
   if (ICmpInst *RHS = dyn_cast<ICmpInst>(I.getOperand(1)))
     if (ICmpInst *LHS = dyn_cast<ICmpInst>(I.getOperand(0)))
-      if (Value *Res = FoldOrOfICmps(LHS, RHS))
+      if (Value *Res = FoldOrOfICmps(LHS, RHS, &I))
         return ReplaceInstUsesWith(I, Res);
 
   // (fcmp uno x, c) | (fcmp uno y, c)  -> (fcmp uno x, y)
@@ -2331,7 +2338,7 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
         // cast is otherwise not optimizable.  This happens for vector sexts.
         if (ICmpInst *RHS = dyn_cast<ICmpInst>(Op1COp))
           if (ICmpInst *LHS = dyn_cast<ICmpInst>(Op0COp))
-            if (Value *Res = FoldOrOfICmps(LHS, RHS))
+            if (Value *Res = FoldOrOfICmps(LHS, RHS, &I))
               return CastInst::Create(Op0C->getOpcode(), Res, I.getType());
 
         // If this is or(cast(fcmp), cast(fcmp)), try to fold this even if the
@@ -2387,7 +2394,7 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
   if (Value *V = SimplifyVectorOp(I))
     return ReplaceInstUsesWith(I, V);
 
-  if (Value *V = SimplifyXorInst(Op0, Op1, DL))
+  if (Value *V = SimplifyXorInst(Op0, Op1, DL, TLI, DT, AT))
     return ReplaceInstUsesWith(I, V);
 
   // (A&B)^(A&C) -> A&(B^C) etc
@@ -2489,7 +2496,8 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
           }
         } else if (Op0I->getOpcode() == Instruction::Or) {
           // (X|C1)^C2 -> X^(C1|C2) iff X&~C1 == 0
-          if (MaskedValueIsZero(Op0I->getOperand(0), Op0CI->getValue())) {
+          if (MaskedValueIsZero(Op0I->getOperand(0), Op0CI->getValue(),
+                                0, &I)) {
             Constant *NewRHS = ConstantExpr::getOr(Op0CI, RHS);
             // Anything in both C1 and C2 is known to be zero, remove it from
             // NewRHS.