[ELF][PPC64]Workaround bogus Visual Studio build warning

[jhenderson]

Summary

Visual Studio has a bug where it converts the integer literal 2147483648 into an unsigned int instead of a long long (i.e. it follows C89 rules). The bug has been reported as https://developercommunity.visualstudio.com/content/problem/141813/-2147483648-c4146-error.html. Because of this bug, we were getting a signed/unsigned comparison warning in VS2015 from the old code (the subsequent unary negation had no effect on the type).

[jhenderson]

http://lab.llvm.org:8011/builders/lld-x86_64-win7/builds/28829 is an example build showing the warning.

[sfertile]

Thanks for cleaning this up. LGTM.

We could also fix this by using INT32_MIN or std::numeric_limts<int32_t>::min(), if preferred

Personally I prefer either of those over the raw numeric literal.

[jhenderson]

Use numeric_limits instead of literal.

[jhenderson]

In D53821#1279012, @sfertile wrote:

Thanks for cleaning this up. LGTM.

We could also fix this by using INT32_MIN or std::numeric_limts<int32_t>::min(), if preferred

Personally I prefer either of those over the raw numeric literal.

Thanks, I've updated it, and will land the patch tomorrow, as I'm just leaving the office now.

lld/trunk/ELF/Arch/PPC64.cpp

bool PPC64::adjustPrologueForCrossSplitStack(uint8_t *Loc, uint8_t *End,
   if (!CheckRegOperands(FirstInstr, 12, 1))
     return false;
   if (SecondInstr != 0x60000000 && !CheckRegOperands(SecondInstr, 12, 12))
     return false;
 
   int32_t StackFrameSize = (HiImm * 65536) + LoImm;
   // Check that the adjusted size doesn't overflow what we can represent with 2
   // instructions.
-  if (StackFrameSize < -2147483648 + Config->SplitStackAdjustSize) {
+  if (StackFrameSize <
+      std::numeric_limits<int32_t>::min() + Config->SplitStackAdjustSize) {
     error(getErrorLocation(Loc) + "split-stack prologue adjustment overflows");
     return false;
   }
 
   int32_t AdjustedStackFrameSize =
       StackFrameSize - Config->SplitStackAdjustSize;
 
   LoImm = AdjustedStackFrameSize & 0xFFFF;