[llvm] [VPlan] Refine DerivedIV nowrap contract (PR #205908)

[Florian Hahn via llvm-commits]

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@@ -4008,12 +4016,22 @@ static void expandVPDerivedIV(VPDerivedIVRecipe *R) {
   case InductionDescriptor::IK_IntInduction: {
     assert(Index->getScalarType() == Start->getScalarType() &&
            "Index type does not match StartValue type");
+    VPIRFlags::WrapFlagsTy NW;
+    auto *RFlags = dyn_cast<VPRecipeWithIRFlags>(Index);
+    if (RFlags && RFlags->hasNoWrapFlags())
+      NW = RFlags->getNoWrapFlags();
     return R->replaceAllUsesWith(Builder.createAdd(
-        Start, Builder.createOverflowingOp(Instruction::Mul, {Index, Step})));
+        Start,
+        Builder.createOverflowingOp(Instruction::Mul, {Index, Step},
+                                    R->getNoWrapFlags()),
+        R->getDebugLoc(), "", NW));
   }
   case InductionDescriptor::IK_PtrInduction:
-    return R->replaceAllUsesWith(Builder.createPtrAdd(
-        Start, Builder.createOverflowingOp(Instruction::Mul, {Index, Step})));
+    return R->replaceAllUsesWith(Builder.createNoWrapPtrAdd(
+        Start,
+        Builder.createOverflowingOp(Instruction::Mul, {Index, Step},
+                                    R->getNoWrapFlags(), R->getDebugLoc()),
+        GEPNoWrapFlags::noUnsignedSignedWrap()));
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fhahn wrote:

I think here we also need to check the flags from the induction, otherwsie we may add `nusw` to a pointer induction formed by a GEP w/o nusw, making the result more poisonous? https://alive2.llvm.org/ce/z/oU4fiA


https://github.com/llvm/llvm-project/pull/205908