[scan-build] fix warnings emitted on LLVM TargetRecip code base

[apelete]

Summary

Fix logic error warnings of the type "called C++ object pointer is
null" emitted by Clang Static Analyzer on the following files:

• lib/Target/TargetRecip.cpp.

Signed-off-by: Apelete Seketeli <[e-mail]>

[dblaikie]

lib/Target/TargetRecip.cpp

74

Does msan ever diagnose this as use-of-uninitialized? Or is this only used in the codepaths where it is initialized?

[spatel]

lib/Target/TargetRecip.cpp

74

The intent was that RefSteps could only be used when RefStepString is valid and therefore not empty (see 'report_fatal_error' just above this). Could this be a false positive from scan-build?

[apelete]

lib/Target/TargetRecip.cpp

74

This one looks like a false positive indeed: scan-build seems unable to see that RefSteps is initialized in parseRefinementStep() below.
Should I remove the initializations here and ignore the warnings ?

[spatel]

lib/Target/TargetRecip.cpp

74

Yes, initializing to '0' could mask an actual problem. You could add asserts of the RefSteps value [0-9] just after the calls to parseRefinementStep() if that would make scan-build happier.

[apelete]

lib/Target/TargetRecip.cpp

74

Assert on RefSteps <= 9 does not suppress the "assigned value is garbage or undefined" warnings on lines 105, 155 and 161 below in this case.
Ignoring the warnings in this file sound like the sanest thing to do.

[spatel]

lib/Target/TargetRecip.cpp

74

Right - if we can't avoid the false positives, let's leave it alone.

[spatel]

abandon?

lib/Target/TargetRecip.cpp

 }
 
 bool TargetRecip::parseGlobalParams(const std::string &Arg) {
   StringRef ArgSub = Arg;
 
   // Look for an optional setting of the number of refinement steps needed
   // for this type of reciprocal operation.
   size_t RefPos;
-  uint8_t RefSteps;
+  uint8_t RefSteps = 0;
   StringRef RefStepString;
   if (parseRefinementStep(ArgSub, RefPos, RefSteps)) {
     // Split the string for further processing.
     RefStepString = ArgSub.substr(RefPos + 1);
     ArgSub = ArgSub.substr(0, RefPos);
   }
   bool Enable;
   bool UseDefaults;
for (unsigned i = 0; i != NumArgs; ++i) {
     StringRef Val = Args[i];
     
     bool IsDisabled = Val[0] == DisabledPrefix;
     // Ignore the disablement token for string matching.
     if (IsDisabled)
       Val = Val.substr(1);
     
     size_t RefPos;
-    uint8_t RefSteps;
+    uint8_t RefSteps = 0;
     StringRef RefStepString;
     if (parseRefinementStep(Val, RefPos, RefSteps)) {
       // Split the string for further processing.
       RefStepString = Val.substr(RefPos + 1);
       Val = Val.substr(0, RefPos);
     }
 
     RecipIter Iter = RecipMap.find(Val);