LLVM Changes for alloc_align

[erichkeane]

Summary

GCC has the alloc_align attribute, which is similar to assume_aligned, except the attribute's parameter is the index of the integer parameter that needs aligning to.

This is the required LLVM changes to make this happen.

[erichkeane]

Corresponding Clang changes: https://reviews.llvm.org/D29599

[mehdi_amini]

There is no client of the API in LLVM? Can you link this revision to the one that is using this in Clang?

[mehdi_amini]

In D29598#668138, @mehdi_amini wrote:

There is no client of the API in LLVM? Can you link this revision to the one that is using this in Clang?

Nevermind our messages crossed :)

[erichkeane]

Mehdi- Did you get a chance to take a look at this?

Thanks!
-Erich

[erichkeane]

Ping!

[myatsina]

include/llvm/IR/IRBuilder.h

1810

Please add function documentation here as well.

1876

I think we should do a signed cast. If the original value is negative, then we want to preserve it and then choose "0".

[erichkeane]

Thanks for the review! Changes made.

[myatsina]

include/llvm/IR/IRBuilder.h

1879

Sorry, I missed this one in my previous comment.
Now, that we are creating a signed cast, the comparison should be signed as well (ICMP_SGT).
This will also affect the tests in the clang part of the review.

[erichkeane]

Implement Marina's sign compare correction.

[myatsina]

LGTM

include/llvm/IR/IRBuilder.h

Value *CreateExtractInteger(const DataLayout &DL, Value *From,
     assert(ExtractedTy->getBitWidth() <= IntTy->getBitWidth() &&
            "Cannot extract to a larger integer!");
     if (ExtractedTy != IntTy) {
       V = CreateTrunc(V, ExtractedTy, Name + ".trunc");
     }
     return V;
   }
 
-  /// \brief Create an assume intrinsic call that represents an alignment
-  /// assumption on the provided pointer.
-  ///
-  /// An optional offset can be provided, and if it is provided, the offset
-  /// must be subtracted from the provided pointer to get the pointer with the
-  /// specified alignment.
-  CallInst *CreateAlignmentAssumption(const DataLayout &DL, Value *PtrValue,
-                                      unsigned Alignment,
-                                      Value *OffsetValue = nullptr) {
-    assert(isa<PointerType>(PtrValue->getType()) &&
-           "trying to create an alignment assumption on a non-pointer?");
-
-    PointerType *PtrTy = cast<PointerType>(PtrValue->getType());
-    Type *IntPtrTy = getIntPtrTy(DL, PtrTy->getAddressSpace());
+private:
+  /// \brief Helper function that creates an assume intrinsic call that
+  /// represents an alignment assumption on the provided Ptr, Mask, Type
+  /// and Offset.
+  CallInst *CreateAlignmentAssumptionHelper(const DataLayout &DL,
+                                            Value *PtrValue, Value *Mask,
+                                            Type *IntPtrTy,
+                                            Value *OffsetValue) {
     Value *PtrIntValue = CreatePtrToInt(PtrValue, IntPtrTy, "ptrint");
 
-    Value *Mask = ConstantInt::get(IntPtrTy,
-      Alignment > 0 ? Alignment - 1 : 0);
     if (OffsetValue) {
       bool IsOffsetZero = false;
       if (ConstantInt *CI = dyn_cast<ConstantInt>(OffsetValue))
         IsOffsetZero = CI->isZero();
 
       if (!IsOffsetZero) {
         if (OffsetValue->getType() != IntPtrTy)
           OffsetValue = CreateIntCast(OffsetValue, IntPtrTy, /*isSigned*/ true,
                                       "offsetcast");
         PtrIntValue = CreateSub(PtrIntValue, OffsetValue, "offsetptr");
       }
     }
 
     Value *Zero = ConstantInt::get(IntPtrTy, 0);
     Value *MaskedPtr = CreateAnd(PtrIntValue, Mask, "maskedptr");
     Value *InvCond = CreateICmpEQ(MaskedPtr, Zero, "maskcond");
-
     return CreateAssumption(InvCond);
   }
+
+public:
+  /// \brief Create an assume intrinsic call that represents an alignment
+  /// assumption on the provided pointer.
+  ///
+  /// An optional offset can be provided, and if it is provided, the offset
+  /// must be subtracted from the provided pointer to get the pointer with the
+  /// specified alignment.
+  CallInst *CreateAlignmentAssumption(const DataLayout &DL, Value *PtrValue,
+                                      unsigned Alignment,
+                                      Value *OffsetValue = nullptr) {
+    assert(isa<PointerType>(PtrValue->getType()) &&
+           "trying to create an alignment assumption on a non-pointer?");
+    PointerType *PtrTy = cast<PointerType>(PtrValue->getType());
+    Type *IntPtrTy = getIntPtrTy(DL, PtrTy->getAddressSpace());
+
+    Value *Mask = ConstantInt::get(IntPtrTy, Alignment > 0 ? Alignment - 1 : 0);
+    return CreateAlignmentAssumptionHelper(DL, PtrValue, Mask, IntPtrTy,
+                                           OffsetValue);
+  }
+  //
+  /// \brief Create an assume intrinsic call that represents an alignment
+  /// assumption on the provided pointer.
+  ///
+  /// An optional offset can be provided, and if it is provided, the offset
+  /// must be subtracted from the provided pointer to get the pointer with the
+  /// specified alignment.
+  ///
+  /// This overload handles the condition where the Alignment is dependent
+  /// on an existing value rather than a static value.
+  CallInst *CreateAlignmentAssumption(const DataLayout &DL, Value *PtrValue,
+                                      Value *Alignment,
+                                      Value *OffsetValue = nullptr) {
+    assert(isa<PointerType>(PtrValue->getType()) &&
+           "trying to create an alignment assumption on a non-pointer?");
+    PointerType *PtrTy = cast<PointerType>(PtrValue->getType());
+    Type *IntPtrTy = getIntPtrTy(DL, PtrTy->getAddressSpace());
+
+    if (Alignment->getType() != IntPtrTy)
+      Alignment = CreateIntCast(Alignment, IntPtrTy, /*isSigned*/ true,
+                                "alignmentcast");
+    Value *IsPositive =
+        CreateICmp(CmpInst::ICMP_UGT, Alignment,
+                   ConstantInt::get(Alignment->getType(), 0), "ispositive");
+    Value *PositiveMask =
+        CreateSub(Alignment, ConstantInt::get(IntPtrTy, 1), "positivemask");
+    Value *Mask = CreateSelect(IsPositive, PositiveMask,
+                               ConstantInt::get(IntPtrTy, 0), "mask");
+
+    return CreateAlignmentAssumptionHelper(DL, PtrValue, Mask, IntPtrTy,
+                                           OffsetValue);
+  }
 };
 
 // Create wrappers for C Binding types (see CBindingWrapping.h).
 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(IRBuilder<>, LLVMBuilderRef)
 
 } // end namespace llvm
 
 #endif // LLVM_IR_IRBUILDER_H