[PATCH] D137847: [ConstraintElimination] Make decompose() infallible

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added a reviewer: fhahn.
Herald added a subscriber: hiraditya.
Herald added a project: All.
nikic requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

decompose() currently returns a mix of `{}` and `0 + 1*V` on failure. I don't really follow why we use one over the other in some cases. It seems like it would be better to make decompose() infallible and always return `0 + 1*V` is we can't decompose the value further.


https://reviews.llvm.org/D137847

Files:
  llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
  llvm/test/Transforms/ConstraintElimination/large-constant-ints.ll


Index: llvm/test/Transforms/ConstraintElimination/large-constant-ints.ll
===================================================================
--- llvm/test/Transforms/ConstraintElimination/large-constant-ints.ll
+++ llvm/test/Transforms/ConstraintElimination/large-constant-ints.ll
@@ -105,7 +105,7 @@
 ; CHECK:       then:
 ; CHECK-NEXT:    [[SUB_1:%.*]] = sub nuw i80 [[A]], 1973801615886922022913
 ; CHECK-NEXT:    [[C_1:%.*]] = icmp ult i80 [[SUB_1]], 1346612317380797267967
-; CHECK-NEXT:    ret i1 [[C_1]]
+; CHECK-NEXT:    ret i1 true
 ; CHECK:       else:
 ; CHECK-NEXT:    ret i1 false
 ;
Index: llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -210,7 +210,7 @@
   // Do not reason about pointers where the index size is larger than 64 bits,
   // as the coefficients used to encode constraints are 64 bit integers.
   if (DL.getIndexTypeSizeInBits(GEP.getPointerOperand()->getType()) > 64)
-    return {};
+    return {{0, nullptr}, {1, &GEP}};
 
   if (!GEP.isInBounds())
     return {{0, nullptr}, {1, &GEP}};
@@ -226,7 +226,7 @@
     auto GTI = gep_type_begin(GEP);
     // Bail out for scalable vectors for now.
     if (isa<ScalableVectorType>(GTI.getIndexedType()))
-      return {};
+      return {{0, nullptr}, {1, &GEP}};
     int64_t Scale = static_cast<int64_t>(
         DL.getTypeAllocSize(GTI.getIndexedType()).getFixedSize());
 
@@ -253,7 +253,7 @@
 
     // Bail out for scalable vectors for now.
     if (isa<ScalableVectorType>(GTI.getIndexedType()))
-      return {};
+      return {{0, nullptr}, {1, &GEP}};
 
     // Struct indices must be constants (and reference an existing field). Add
     // them to the constant factor.
@@ -304,8 +304,6 @@
                             bool IsSignedB) -> SmallVector<DecompEntry, 4> {
     auto ResA = decompose(A, Preconditions, IsSigned, DL);
     auto ResB = decompose(B, Preconditions, IsSignedB, DL);
-    if (ResA.empty() || ResB.empty())
-      return {};
     ResA[0].Coefficient += ResB[0].Coefficient;
     append_range(ResA, drop_begin(ResB));
     return ResA;
@@ -327,7 +325,7 @@
 
   if (auto *CI = dyn_cast<ConstantInt>(V)) {
     if (CI->uge(MaxConstraintValue))
-      return {};
+      return {{0, nullptr}, {1, V}};
     return {{int64_t(CI->getZExtValue()), nullptr}};
   }
 
@@ -434,10 +432,6 @@
                         Preconditions, IsSigned, DL);
   auto BDec = decompose(Op1->stripPointerCastsSameRepresentation(),
                         Preconditions, IsSigned, DL);
-  // Skip if decomposing either of the values failed.
-  if (ADec.empty() || BDec.empty())
-    return {};
-
   int64_t Offset1 = ADec[0].Coefficient;
   int64_t Offset2 = BDec[0].Coefficient;
   Offset1 *= -1;


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D137847.474774.patch
Type: text/x-patch
Size: 2866 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20221111/4fe89954/attachment.bin>