[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/Target/NVPTX/NVPTXTargetTransformInfo.cpp b/llvm/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp
index e7250cdba5a..6e679dd0257 100644
--- a/llvm/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp
@@ -89,12 +89,12 @@ bool NVPTXTTIImpl::isSourceOfDivergence(const Value *V) {
   return false;
 }
 
-unsigned NVPTXTTIImpl::getArithmeticInstrCost(
+int NVPTXTTIImpl::getArithmeticInstrCost(
     unsigned Opcode, Type *Ty, TTI::OperandValueKind Opd1Info,
     TTI::OperandValueKind Opd2Info, TTI::OperandValueProperties Opd1PropInfo,
     TTI::OperandValueProperties Opd2PropInfo) {
   // Legalize the type.
-  std::pair<unsigned, MVT> LT = TLI->getTypeLegalizationCost(DL, Ty);
+  std::pair<int, MVT> LT = TLI->getTypeLegalizationCost(DL, Ty);
 
   int ISD = TLI->InstructionOpcodeToISD(Opcode);