[PATCH] D97244: [SimplifyCFG] Update passingValueIsAlwaysUndefined to check more attributes
Juneyoung Lee via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Feb 22 18:48:59 PST 2021
aqjune created this revision.
aqjune added reviewers: spatel, nikic, xbolva00, lebedev.ri.
Herald added subscribers: dexonsmith, hiraditya.
aqjune requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.
This is a simple patch to update SimplifyCFG's passingValueIsAlwaysUndefined to inspect more attributes.
A new function `CallBase::isPassingUndefUB` checks attributes that imply noundef.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D97244
Files:
llvm/include/llvm/IR/InstrTypes.h
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6433,8 +6433,8 @@
for (const llvm::Use &Arg : CB->args())
if (Arg == I) {
unsigned ArgIdx = CB->getArgOperandNo(&Arg);
- if (CB->paramHasAttr(ArgIdx, Attribute::NonNull) &&
- CB->paramHasAttr(ArgIdx, Attribute::NoUndef)) {
+ if (CB->isPassingUndefUB(ArgIdx) &&
+ CB->paramHasAttr(ArgIdx, Attribute::NonNull)) {
// Passing null to a nonnnull+noundef argument is undefined.
return !PtrValueMayBeModified;
}
@@ -6444,7 +6444,7 @@
for (const llvm::Use &Arg : CB->args())
if (Arg == I) {
unsigned ArgIdx = CB->getArgOperandNo(&Arg);
- if (CB->paramHasAttr(ArgIdx, Attribute::NoUndef)) {
+ if (CB->isPassingUndefUB(ArgIdx)) {
// Passing undef to a noundef argument is undefined.
return true;
}
Index: llvm/include/llvm/IR/InstrTypes.h
===================================================================
--- llvm/include/llvm/IR/InstrTypes.h
+++ llvm/include/llvm/IR/InstrTypes.h
@@ -1653,6 +1653,17 @@
paramHasAttr(ArgNo, Attribute::Preallocated);
}
+ /// Determine whether passing undef to this argument is undefined behavior.
+ /// If passing undef to this argument is UB, passing poison is UB as well
+ /// because poison is more undefined than undef.
+ bool isPassingUndefUB(unsigned ArgNo) const {
+ return paramHasAttr(ArgNo, Attribute::NoUndef) ||
+ // dereferenceable implies noundef.
+ paramHasAttr(ArgNo, Attribute::Dereferenceable) ||
+ // dereferenceable implies noundef, and null is a well-defined value.
+ paramHasAttr(ArgNo, Attribute::DereferenceableOrNull);
+ }
+
/// Determine if there are is an inalloca argument. Only the last argument can
/// have the inalloca attribute.
bool hasInAllocaArgument() const {
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