[llvm] 098b0b1 - [ConstraintElimination] Transfer info from SGE to unsigned system.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2022-06-22T15:27:59+02:00
New Revision: 098b0b18a7df42434d3cc747c89dd62ddac73afa

URL: https://github.com/llvm/llvm-project/commit/098b0b18a7df42434d3cc747c89dd62ddac73afa
DIFF: https://github.com/llvm/llvm-project/commit/098b0b18a7df42434d3cc747c89dd62ddac73afa.diff

LOG: [ConstraintElimination] Transfer info from SGE to unsigned system.

This patch adds a new transferToOtherSystem helper that tries to
transfer information from signed predicates to the unsigned system and
vice versa.

The initial version adds A >=u B for A >=s B && B >=s 0

https://alive2.llvm.org/ce/z/8b6F9i

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
    llvm/test/Transforms/ConstraintElimination/gep-arithmetic.ll
    llvm/test/Transforms/ConstraintElimination/transfer-signed-facts-to-unsigned.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index 9a3c0ca93bee..f3bbc7708477 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -160,6 +160,12 @@ class ConstraintInfo {
     return getConstraint(Cmp->getPredicate(), Cmp->getOperand(0),
                          Cmp->getOperand(1), NewIndices);
   }
+
+  /// Try to add information from \p A \p Pred \p B to the unsigned/signed
+  /// system if \p Pred is signed/unsigned.
+  void transferToOtherSystem(CmpInst::Predicate Pred, Value *A, Value *B,
+                             bool IsNegated, unsigned NumIn, unsigned NumOut,
+                             SmallVectorImpl<StackEntry> &DFSInStack);
 };
 
 } // namespace
@@ -384,6 +390,27 @@ bool ConstraintInfo::doesHold(CmpInst::Predicate Pred, Value *A,
          getCS(CmpInst::isSigned(Pred)).isConditionImplied(R.Coefficients);
 }
 
+void ConstraintInfo::transferToOtherSystem(
+    CmpInst::Predicate Pred, Value *A, Value *B, bool IsNegated, unsigned NumIn,
+    unsigned NumOut, SmallVectorImpl<StackEntry> &DFSInStack) {
+  // Check if we can combine facts from the signed and unsigned systems to
+  // derive additional facts.
+  if (!A->getType()->isIntegerTy())
+    return;
+  // FIXME: This currently depends on the order we add facts. Ideally we
+  // would first add all known facts and only then try to add additional
+  // facts.
+  switch (Pred) {
+  default:
+    break;
+  case CmpInst::ICMP_SGE:
+    if (doesHold(CmpInst::ICMP_SGE, B, ConstantInt::get(B->getType(), 0))) {
+      addFact(CmpInst::ICMP_UGE, A, B, IsNegated, NumIn, NumOut, DFSInStack);
+    }
+    break;
+  }
+}
+
 namespace {
 /// Represents either a condition that holds on entry to a block or a basic
 /// block, with their respective Dominator DFS in and out numbers.
@@ -766,6 +793,8 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT) {
       // Otherwise, add the condition to the system and stack, if we can
       // transform it into a constraint.
       Info.addFact(Pred, A, B, CB.Not, CB.NumIn, CB.NumOut, DFSInStack);
+      Info.transferToOtherSystem(Pred, A, B, CB.Not, CB.NumIn, CB.NumOut,
+                                 DFSInStack);
     }
   }
 

diff  --git a/llvm/test/Transforms/ConstraintElimination/gep-arithmetic.ll b/llvm/test/Transforms/ConstraintElimination/gep-arithmetic.ll
index c490f72e914f..97537dd96b5f 100644
--- a/llvm/test/Transforms/ConstraintElimination/gep-arithmetic.ll
+++ b/llvm/test/Transforms/ConstraintElimination/gep-arithmetic.ll
@@ -368,7 +368,7 @@ define i4 @ptr_N_and_step_signed_positive_explicit_check_constant_step(i8* %src,
 ; CHECK:       step.check:
 ; CHECK-NEXT:    [[STEP_UGE_0:%.*]] = icmp uge i16 [[STEP]], 0
 ; CHECK-NEXT:    [[STEP_ULT_N:%.*]] = icmp ult i16 [[STEP]], [[N]]
-; CHECK-NEXT:    [[AND_2:%.*]] = and i1 [[STEP_UGE_0]], [[STEP_ULT_N]]
+; CHECK-NEXT:    [[AND_2:%.*]] = and i1 true, [[STEP_ULT_N]]
 ; CHECK-NEXT:    br i1 [[AND_2]], label [[PTR_CHECK:%.*]], label [[EXIT:%.*]]
 ; CHECK:       ptr.check:
 ; CHECK-NEXT:    [[SRC_STEP:%.*]] = getelementptr inbounds i8, i8* [[SRC]], i16 1

diff  --git a/llvm/test/Transforms/ConstraintElimination/transfer-signed-facts-to-unsigned.ll b/llvm/test/Transforms/ConstraintElimination/transfer-signed-facts-to-unsigned.ll
index 8c9b374c42f8..0eb95323a4d6 100644
--- a/llvm/test/Transforms/ConstraintElimination/transfer-signed-facts-to-unsigned.ll
+++ b/llvm/test/Transforms/ConstraintElimination/transfer-signed-facts-to-unsigned.ll
@@ -275,7 +275,7 @@ define i1 @cnt_positive_sge_against_base_with_zext(ptr %p, i32 %cnt) {
 ; CHECK-NEXT:    [[EXT:%.*]] = zext i32 [[CNT]] to i64
 ; CHECK-NEXT:    [[ADD_PTR:%.*]] = getelementptr inbounds i32, ptr [[P:%.*]], i64 [[EXT]]
 ; CHECK-NEXT:    [[CMP_1:%.*]] = icmp uge ptr [[ADD_PTR]], [[P]]
-; CHECK-NEXT:    br i1 [[CMP_1]], label [[THEN:%.*]], label [[ELSE:%.*]]
+; CHECK-NEXT:    br i1 true, label [[THEN:%.*]], label [[ELSE:%.*]]
 ; CHECK:       then:
 ; CHECK-NEXT:    ret i1 false
 ; CHECK:       else:
@@ -497,11 +497,11 @@ define i1 @sge_2(i8 %idx) {
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[CMP]])
 ; CHECK-NEXT:    [[T_1:%.*]] = icmp uge i8 [[IDX]], 2
 ; CHECK-NEXT:    [[T_2:%.*]] = icmp uge i8 [[IDX]], 1
-; CHECK-NEXT:    [[RES_1:%.*]] = xor i1 [[T_1]], [[T_2]]
+; CHECK-NEXT:    [[RES_1:%.*]] = xor i1 true, true
 ; CHECK-NEXT:    [[C_1:%.*]] = icmp uge i8 [[IDX]], 3
 ; CHECK-NEXT:    [[RES_2:%.*]] = xor i1 [[RES_1]], [[C_1]]
 ; CHECK-NEXT:    [[F_1:%.*]] = icmp ult i8 [[IDX]], 2
-; CHECK-NEXT:    [[RES_3:%.*]] = xor i1 [[RES_2]], [[F_1]]
+; CHECK-NEXT:    [[RES_3:%.*]] = xor i1 [[RES_2]], false
 ; CHECK-NEXT:    ret i1 [[RES_3]]
 ;
 entry: