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As an alternative to https://reviews.llvm.org/D150192, we consider using the
memory region declaration intrinsic, introduced in
https://reviews.llvm.org/D115274, as another way to propagate the semantics of
C/C++ array-indexing rules to LLVM IR.
This patch is only only a proof-of-concept at this point, intended to gather
feedback and bring https://reviews.llvm.org/D115274 back into focus. As was
mentioned there (and as seen from test results), completing this patch would
require patching a lot of optimizations. For example,
`InstructionCombiningPass` works with `GetElementPtrInst`s directly and will
not recognize an intrinsic call as such. Many other passes such as
`IndVarSimplifyPass`, `EarlyCSE`, etc., routinely use a switch case or call
`isa<GetElementPtrInst>()` to detect `GEP`s.
We'd be fine with doing that sort of work, if we get some initial thumbs up
from the community that this is the way to go. Of course, we're also open to
trying a different approach if it avoids the apparently unavoidable complexity
of this one.
Depends on D115274 <https://reviews.llvm.org/D115274>
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D152275
Files:
clang/lib/CodeGen/CGExpr.cpp
Index: clang/lib/CodeGen/CGExpr.cpp
===================================================================
--- clang/lib/CodeGen/CGExpr.cpp
+++ clang/lib/CodeGen/CGExpr.cpp
@@ -3936,10 +3936,44 @@
// Propagate the alignment from the array itself to the result.
QualType arrayType = Array->getType();
- Addr = emitArraySubscriptGEP(
- *this, ArrayLV.getAddress(*this), {CGM.getSize(CharUnits::Zero()),
Idx},
- E->getType(), !getLangOpts().isSignedOverflowDefined(), SignedIndices,
- E->getExprLoc(), &arrayType, E->getBase());
+
+ Address ArrayLVAddr = ArrayLV.getAddress(*this);
+
+ if (!getLangOpts().isSignedOverflowDefined() &&
+ // ISO/IEC 9899:TC3, 6.5.6.8
+ (getLangOpts().C99 || getLangOpts().CPlusPlus) &&
+ getContext().getAsConstantArrayType(arrayType)) {
+ auto *CAT = getContext().getAsConstantArrayType(arrayType);
+ uint64_t BoundedRegionSize = (Idx->getType()->getScalarSizeInBits() / 8)
*
+ CAT->getSize().getZExtValue();
+
+ Address BeginOff = emitArraySubscriptGEP(
+ *this, ArrayLVAddr,
+ {CGM.getSize(CharUnits::Zero()), CGM.getSize(CharUnits::Zero())},
+ E->getType(), !getLangOpts().isSignedOverflowDefined(),
SignedIndices,
+ E->getExprLoc(), &arrayType, E->getBase());
+
+ llvm::Function *F =
CGM.getIntrinsic(llvm::Intrinsic::memory_region_decl,
+ BeginOff.getPointer()->getType());
+ llvm::Value *Call = Builder.CreateCall(F,
+ {BeginOff.getPointer(),
+ llvm::ConstantInt::get(Int64Ty, 0),
+ llvm::ConstantInt::get(Int64Ty, BoundedRegionSize)},
+ "arrayidx.bounded");
+ Address RetAddr(Call, BeginOff.getElementType(),
+ ArrayLVAddr.getAlignment());
+
+ Addr = emitArraySubscriptGEP(
+ *this, RetAddr, {Idx},
+ E->getType(), !getLangOpts().isSignedOverflowDefined(),
SignedIndices,
+ E->getExprLoc(), &arrayType, E->getBase());
+ } else {
+ Addr = emitArraySubscriptGEP(
+ *this, ArrayLVAddr, {CGM.getSize(CharUnits::Zero()), Idx},
+ E->getType(), !getLangOpts().isSignedOverflowDefined(),
SignedIndices,
+ E->getExprLoc(), &arrayType, E->getBase());
+ }
+
EltBaseInfo = ArrayLV.getBaseInfo();
EltTBAAInfo = CGM.getTBAAInfoForSubobject(ArrayLV, E->getType());
} else {
Index: clang/lib/CodeGen/CGExpr.cpp
===================================================================
--- clang/lib/CodeGen/CGExpr.cpp
+++ clang/lib/CodeGen/CGExpr.cpp
@@ -3936,10 +3936,44 @@
// Propagate the alignment from the array itself to the result.
QualType arrayType = Array->getType();
- Addr = emitArraySubscriptGEP(
- *this, ArrayLV.getAddress(*this), {CGM.getSize(CharUnits::Zero()), Idx},
- E->getType(), !getLangOpts().isSignedOverflowDefined(), SignedIndices,
- E->getExprLoc(), &arrayType, E->getBase());
+
+ Address ArrayLVAddr = ArrayLV.getAddress(*this);
+
+ if (!getLangOpts().isSignedOverflowDefined() &&
+ // ISO/IEC 9899:TC3, 6.5.6.8
+ (getLangOpts().C99 || getLangOpts().CPlusPlus) &&
+ getContext().getAsConstantArrayType(arrayType)) {
+ auto *CAT = getContext().getAsConstantArrayType(arrayType);
+ uint64_t BoundedRegionSize = (Idx->getType()->getScalarSizeInBits() / 8) *
+ CAT->getSize().getZExtValue();
+
+ Address BeginOff = emitArraySubscriptGEP(
+ *this, ArrayLVAddr,
+ {CGM.getSize(CharUnits::Zero()), CGM.getSize(CharUnits::Zero())},
+ E->getType(), !getLangOpts().isSignedOverflowDefined(), SignedIndices,
+ E->getExprLoc(), &arrayType, E->getBase());
+
+ llvm::Function *F = CGM.getIntrinsic(llvm::Intrinsic::memory_region_decl,
+ BeginOff.getPointer()->getType());
+ llvm::Value *Call = Builder.CreateCall(F,
+ {BeginOff.getPointer(),
+ llvm::ConstantInt::get(Int64Ty, 0),
+ llvm::ConstantInt::get(Int64Ty, BoundedRegionSize)},
+ "arrayidx.bounded");
+ Address RetAddr(Call, BeginOff.getElementType(),
+ ArrayLVAddr.getAlignment());
+
+ Addr = emitArraySubscriptGEP(
+ *this, RetAddr, {Idx},
+ E->getType(), !getLangOpts().isSignedOverflowDefined(), SignedIndices,
+ E->getExprLoc(), &arrayType, E->getBase());
+ } else {
+ Addr = emitArraySubscriptGEP(
+ *this, ArrayLVAddr, {CGM.getSize(CharUnits::Zero()), Idx},
+ E->getType(), !getLangOpts().isSignedOverflowDefined(), SignedIndices,
+ E->getExprLoc(), &arrayType, E->getBase());
+ }
+
EltBaseInfo = ArrayLV.getBaseInfo();
EltTBAAInfo = CGM.getTBAAInfoForSubobject(ArrayLV, E->getType());
} else {
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