r205646 - Vector [Sema]. Vector "splats" which are truncated should have a warning

[Stephen Canon]

Hi Fariborz --

Before this patch, we were generating the following warning for your test case:

	implicit conversion loses integer precision: 'uint32_t' (aka 'unsigned int') to 'ushort16'

with your patch, we get the following instead:

	implicit conversion loses integer precision: 'uint32_t' (aka 'unsigned int') to 'unsigned short'

I have a slight preference for the warning we used to issue, as it refers to the conversion that actually takes place conceptually (scalar -> vector), rather than the "subconversion" that changes the value (scalar -> vector element).  Reasonable people may disagree, of course.

– Steve

On Apr 4, 2014, at 3:33 PM, Fariborz Jahanian <fjahanian at apple.com> wrote:

> Author: fjahanian
> Date: Fri Apr  4 14:33:39 2014
> New Revision: 205646
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=205646&view=rev
> Log:
> Vector [Sema]. Vector "splats" which are truncated should have a warning
> with -Wconversion. // rdar://16502418
> 
> Modified:
>    cfe/trunk/lib/Sema/SemaChecking.cpp
>    cfe/trunk/test/Sema/conversion.c
> 
> Modified: cfe/trunk/lib/Sema/SemaChecking.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=205646&r1=205645&r2=205646&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Sema/SemaChecking.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaChecking.cpp Fri Apr  4 14:33:39 2014
> @@ -6113,11 +6113,20 @@ void CheckConditionalOperator(Sema &S, C
> /// implicit conversions in the given expression.  There are a couple
> /// of competing diagnostics here, -Wconversion and -Wsign-compare.
> void AnalyzeImplicitConversions(Sema &S, Expr *OrigE, SourceLocation CC) {
> -  QualType T = OrigE->getType();
>   Expr *E = OrigE->IgnoreParenImpCasts();
> 
>   if (E->isTypeDependent() || E->isValueDependent())
>     return;
> +  
> +  QualType T = OrigE->getType();
> +  // Check for conversion from an arithmetic type to a vector of arithmetic
> +  // type elements. Warn if this results in truncation of each vector element.
> +  if (isa<ExtVectorElementExpr>(E)) {
> +    if (ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(OrigE))
> +      if ((ICE->getCastKind() == CK_VectorSplat) &&
> +          !T.isNull() && T->isExtVectorType())
> +        T = cast<ExtVectorType>(T.getCanonicalType())->getElementType();
> +  }
> 
>   // For conditional operators, we analyze the arguments as if they
>   // were being fed directly into the output.
> 
> Modified: cfe/trunk/test/Sema/conversion.c
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/conversion.c?rev=205646&r1=205645&r2=205646&view=diff
> ==============================================================================
> --- cfe/trunk/test/Sema/conversion.c (original)
> +++ cfe/trunk/test/Sema/conversion.c Fri Apr  4 14:33:39 2014
> @@ -417,3 +417,15 @@ void test26(int si, long sl) {
>   si = si / sl;
>   si = sl / si; // expected-warning {{implicit conversion loses integer precision: 'long' to 'int'}}
> }
> +
> +// rdar://16502418
> +typedef unsigned short uint16_t;
> +typedef unsigned int uint32_t;
> +typedef __attribute__ ((ext_vector_type(16),__aligned__(32))) uint16_t ushort16;
> +typedef __attribute__ ((ext_vector_type( 8),__aligned__( 32))) uint32_t uint8;
> +
> +void test27(ushort16 constants) {
> +    uint8 pairedConstants = (uint8) constants;
> +    ushort16 crCbScale = pairedConstants.s4; // expected-warning {{implicit conversion loses integer precision: 'uint32_t' (aka 'unsigned int') to 'unsigned short'}}
> +    ushort16 brBias = pairedConstants.s6; // expected-warning {{implicit conversion loses integer precision: 'uint32_t' (aka 'unsigned int') to 'unsigned short'}}
> +}
> 
> 
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