[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, 4 insertions, 5 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.h b/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.h
index 4b80973ed87..c74c73b10f4 100644
--- a/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.h
+++ b/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.h
@@ -42,12 +42,11 @@ public:
   /// \name Scalar TTI Implementations
   /// @{
 
-  unsigned getIntImmCost(const APInt &Imm, Type *Ty);
+  int getIntImmCost(const APInt &Imm, Type *Ty);
 
-  unsigned getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm,
-                         Type *Ty);
-  unsigned getIntImmCost(Intrinsic::ID IID, unsigned Idx, const APInt &Imm,
-                         Type *Ty);
+  int getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm, Type *Ty);
+  int getIntImmCost(Intrinsic::ID IID, unsigned Idx, const APInt &Imm,
+                    Type *Ty);
 
   TTI::PopcntSupportKind getPopcntSupport(unsigned TyWidth);