[TTI] Make the cost APIs in TargetTransformInfo consistently use 'int'

rather than 'unsigned' for their costs.

For something like costs in particular there is a natural "negative"
value, that of savings or saved cost. As a consequence, there is a lot
of code that subtracts or creates negative values based on cost, all of
which is prone to awkwardness or bugs when dealing with an unsigned
type. Similarly, we *never* want these values to wrap, as that would
cause Very Bad code generation (likely percieved as an infinite loop as
we try to emit over 2^32 instructions or some such insanity).

All around 'int' seems a much better fit for these basic metrics. I've
added asserts to ensure that at least the TTI interface never returns
negative numbers here. If we ever have a use case for negative numbers,
we can remove this, but this way a bug where someone used '-1' to
produce a 'very large' cost will be caught by the assert.

This passes all tests, and is also UBSan clean.

No functional change intended.

Differential Revision: http://reviews.llvm.org/D11741

llvm-svn: 244080

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
index 0e10b2f2e11..a6e8e43e869 100644
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -1634,13 +1634,13 @@ int TargetLoweringBase::InstructionOpcodeToISD(unsigned Opcode) const {
   llvm_unreachable("Unknown instruction type encountered!");
 }
 
-std::pair<unsigned, MVT>
+std::pair<int, MVT>
 TargetLoweringBase::getTypeLegalizationCost(const DataLayout &DL,
                                             Type *Ty) const {
   LLVMContext &C = Ty->getContext();
   EVT MTy = getValueType(DL, Ty);
 
-  unsigned Cost = 1;
+  int Cost = 1;
   // We keep legalizing the type until we find a legal kind. We assume that
   // the only operation that costs anything is the split. After splitting
   // we need to handle two types.