[cfe-dev] Question about ASTContext::getPromotedIntegerType() function

[JinGu Kang]

Hi all,

I have a question about ASTContext::getPromotedIntegerType() function.

I have tested a code as following:

source code:
int main()
{
   volatile unsigned short x;
   volatile unsigned short y;
   volatile unsigned short result;

   x = 8;
   y = 2;

   result = x / y;

   return 0;
}

Generated IR from clang:
   6 define i32 @main() #0 {
   7 entry:
   8   %retval = alloca i32, align 4
   9   %x = alloca i16, align 2
  10   %y = alloca i16, align 2
  11   %result = alloca i16, align 2
  12   store i32 0, i32* %retval
  13   store volatile i16 8, i16* %x, align 2
  14   store volatile i16 2, i16* %y, align 2
  15   %0 = load volatile i16* %x, align 2
  16   %conv = zext i16 %0 to i32
  17   %1 = load volatile i16* %y, align 2
  18   %conv1 = zext i16 %1 to i32
  19   %div = sdiv i32 %conv, %conv1
  20   %conv2 = trunc i32 %div to i16
  21   store volatile i16 %conv2, i16* %result, align 2
  22   ret i32 0
  23 }

I expected "udiv" instruction on line 19 but there was "sdiv" 
instruction because of "ASTContext::getPromotedIntegerType()" function 
promotes "unsigned short" to "int".

Could someone explain why this function returns "IntTy" when 
"PromotableSize" is not same with "IntSize"? I think that the line of 
"ASTContext::getPromotedIntegerType()" function should be changed.
ex)
return (PromotableSize != IntSize) ? IntTy : UnsignedIntTy;
--> return UnsignedIntTy;

Thanks,
JinGu Kang


-- 
JinGu Kang
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-------------- next part --------------
Index: lib/AST/ASTContext.cpp
===================================================================
--- lib/AST/ASTContext.cpp	(revision 186398)
+++ lib/AST/ASTContext.cpp	(working copy)
@@ -4369,7 +4369,7 @@
   uint64_t PromotableSize = getIntWidth(Promotable);
   uint64_t IntSize = getIntWidth(IntTy);
   assert(Promotable->isUnsignedIntegerType() && PromotableSize <= IntSize);
-  return (PromotableSize != IntSize) ? IntTy : UnsignedIntTy;
+  return UnsignedIntTy;
 }
 
 /// \brief Recurses in pointer/array types until it finds an objc retainable