[SCEV] Transfer gep nusw and nuw flags

nusw implies nsw offset and nuw base+offset arithmetic if offset
is non-negative. nuw implies nuw offset and base+offset arithmetic.
As usual, we can only transfer is poison implies UB.

1 files changed, 14 insertions, 11 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 7d3e3f4..8d90530 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3746,21 +3746,23 @@ ScalarEvolution::getGEPExpr(GEPOperator *GEP,
   // getSCEV(Base)->getType() has the same address space as Base->getType()
   // because SCEV::getType() preserves the address space.
   Type *IntIdxTy = getEffectiveSCEVType(BaseExpr->getType());
-  const bool AssumeInBoundsFlags = [&]() {
-    if (!GEP->isInBounds())
-      return false;
-
+  GEPNoWrapFlags NW = GEP->getNoWrapFlags();
+  if (NW != GEPNoWrapFlags::none()) {
     // We'd like to propagate flags from the IR to the corresponding SCEV nodes,
     // but to do that, we have to ensure that said flag is valid in the entire
     // defined scope of the SCEV.
-    auto *GEPI = dyn_cast<Instruction>(GEP);
     // TODO: non-instructions have global scope.  We might be able to prove
     // some global scope cases
-    return GEPI && isSCEVExprNeverPoison(GEPI);
-  }();
+    auto *GEPI = dyn_cast<Instruction>(GEP);
+    if (!GEPI || !isSCEVExprNeverPoison(GEPI))
+      NW = GEPNoWrapFlags::none();
+  }
 
-  SCEV::NoWrapFlags OffsetWrap =
-    AssumeInBoundsFlags ? SCEV::FlagNSW : SCEV::FlagAnyWrap;
+  SCEV::NoWrapFlags OffsetWrap = SCEV::FlagAnyWrap;
+  if (NW.hasNoUnsignedSignedWrap())
+    OffsetWrap = setFlags(OffsetWrap, SCEV::FlagNSW);
+  if (NW.hasNoUnsignedWrap())
+    OffsetWrap = setFlags(OffsetWrap, SCEV::FlagNUW);
 
   Type *CurTy = GEP->getType();
   bool FirstIter = true;
@@ -3806,8 +3808,9 @@ ScalarEvolution::getGEPExpr(GEPOperator *GEP,
   // Add the base address and the offset. We cannot use the nsw flag, as the
   // base address is unsigned. However, if we know that the offset is
   // non-negative, we can use nuw.
-  SCEV::NoWrapFlags BaseWrap = AssumeInBoundsFlags && isKnownNonNegative(Offset)
-                                   ? SCEV::FlagNUW : SCEV::FlagAnyWrap;
+  bool NUW = NW.hasNoUnsignedWrap() ||
+             (NW.hasNoUnsignedSignedWrap() && isKnownNonNegative(Offset));
+  SCEV::NoWrapFlags BaseWrap = NUW ? SCEV::FlagNUW : SCEV::FlagAnyWrap;
   auto *GEPExpr = getAddExpr(BaseExpr, Offset, BaseWrap);
   assert(BaseExpr->getType() == GEPExpr->getType() &&
          "GEP should not change type mid-flight.");