Allow DataLayout to specify addrspace for allocas.

LLVM makes several assumptions about address space 0. However,
alloca is presently constrained to always return this address space.
There's no real way to avoid using alloca, so without this
there is no way to opt out of these assumptions.

The problematic assumptions include:
- That the pointer size used for the stack is the same size as
  the code size pointer, which is also the maximum sized pointer.

- That 0 is an invalid, non-dereferencable pointer value.

These are problems for AMDGPU because alloca is used to
implement the private address space, which uses a 32-bit
index as the pointer value. Other pointers are 64-bit
and behave more like LLVM's notion of generic address
space. By changing the address space used for allocas,
we can change our generic pointer type to be LLVM's generic
pointer type which does have similar properties.

llvm-svn: 299888

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/IR/DataLayout.cpp b/llvm/lib/IR/DataLayout.cpp
index de08f920f09..6f90ce59856 100644
--- a/llvm/lib/IR/DataLayout.cpp
+++ b/llvm/lib/IR/DataLayout.cpp
@@ -174,6 +174,7 @@ void DataLayout::reset(StringRef Desc) {
 
   LayoutMap = nullptr;
   BigEndian = false;
+  AllocaAddrSpace = 0;
   StackNaturalAlign = 0;
   ManglingMode = MM_None;
   NonIntegralAddressSpaces.clear();
@@ -352,6 +353,12 @@ void DataLayout::parseSpecifier(StringRef Desc) {
       StackNaturalAlign = inBytes(getInt(Tok));
       break;
     }
+    case 'A': { // Default stack/alloca address space.
+      AllocaAddrSpace = getInt(Tok);
+      if (!isUInt<24>(AllocaAddrSpace))
+        report_fatal_error("Invalid address space, must be a 24bit integer");
+      break;
+    }
     case 'm':
       if (!Tok.empty())
         report_fatal_error("Unexpected trailing characters after mangling specifier in datalayout string");
@@ -394,6 +401,7 @@ void DataLayout::init(const Module *M) { *this = M->getDataLayout(); }
 
 bool DataLayout::operator==(const DataLayout &Other) const {
   bool Ret = BigEndian == Other.BigEndian &&
+             AllocaAddrSpace == Other.AllocaAddrSpace &&
              StackNaturalAlign == Other.StackNaturalAlign &&
              ManglingMode == Other.ManglingMode &&
              LegalIntWidths == Other.LegalIntWidths &&