[msan] Break the getShadow loop after matching an argument

[eugenis]

LGTM

This is strictly a compilation time optimization, right?

[stephan.yichao.zhao]

In D91320#2392089, @eugenis wrote:

LGTM

This is strictly a compilation time optimization, right?

Yes. Not sure how it can make compilation fast, but imo it would make the code a bit easier to follow.

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

if (Argument *A = dyn_cast<Argument>(V)) {
                      << "  ARG:    " << FArg << " ==> " << **ShadowPtr << "\n");
           if (MS.TrackOrigins && !Overflow) {
             Value *OriginPtr =
                 getOriginPtrForArgument(&FArg, EntryIRB, ArgOffset);
             setOrigin(A, EntryIRB.CreateLoad(MS.OriginTy, OriginPtr));
           } else {
             setOrigin(A, getCleanOrigin());
           }
+
+          break;
         }
 
         if (!FArgEagerCheck)
           ArgOffset += alignTo(Size, kShadowTLSAlignment);
       }
       assert(*ShadowPtr && "Could not find shadow for an argument");
       return *ShadowPtr;
     }