[TargetLowering] StringRefize asm constraint getters.

There is some functional change here because it changes target code from
atoi(3) to StringRef::getAsInteger which has error checking. For valid
constraints there should be no difference.

llvm-svn: 241411
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index 02242b5..ac0734f 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -519,8 +519,7 @@
     MachineBasicBlock *emitEHSjLjLongJmp(MachineInstr *MI,
                                          MachineBasicBlock *MBB) const;
 
-    ConstraintType
-    getConstraintType(const std::string &Constraint) const override;
+    ConstraintType getConstraintType(StringRef Constraint) const override;
 
     /// Examine constraint string and operand type and determine a weight value.
     /// The operand object must already have been set up with the operand type.
@@ -529,8 +528,7 @@
 
     std::pair<unsigned, const TargetRegisterClass *>
     getRegForInlineAsmConstraint(const TargetRegisterInfo *TRI,
-                                 const std::string &Constraint,
-                                 MVT VT) const override;
+                                 StringRef Constraint, MVT VT) const override;
 
     /// getByValTypeAlignment - Return the desired alignment for ByVal aggregate
     /// function arguments in the caller parameter area.  This is the actual
@@ -544,8 +542,8 @@
                                       std::vector<SDValue> &Ops,
                                       SelectionDAG &DAG) const override;
 
-    unsigned getInlineAsmMemConstraint(
-        const std::string &ConstraintCode) const override {
+    unsigned
+    getInlineAsmMemConstraint(StringRef ConstraintCode) const override {
       if (ConstraintCode == "es")
         return InlineAsm::Constraint_es;
       else if (ConstraintCode == "o")