[cfe-commits] [PATCH] FP_CONTRACT pragma support.

[Douglas Gregor]

On Sep 26, 2012, at 10:22 PM, Lang Hames <lhames at gmail.com> wrote:

> Hi Hal,
> 
> Sorry - that was an oversight on my part. I've now added support for expressions of the form (a * b - c) and (c - a * b). Adding that feature also prompted me to refactor some of the codegen logic, and testing helped me find a couple of bugs where I'd failed to propagate the contractable bit during template instantiation.
> 
> Updated patch attached.

Index: include/clang/AST/Expr.h
===================================================================
--- include/clang/AST/Expr.h	(revision 164758)
+++ include/clang/AST/Expr.h	(working copy)
@@ -2782,6 +2782,7 @@
 
 private:
   unsigned Opc : 6;
+  bool FPContractable : 1;
   SourceLocation OpLoc;
 
   enum { LHS, RHS, END_EXPR };

Please use 'unsigned' rather than 'bool' (due to MSVC packing rules).

@@ -2790,7 +2791,7 @@
 
   BinaryOperator(Expr *lhs, Expr *rhs, Opcode opc, QualType ResTy,
                  ExprValueKind VK, ExprObjectKind OK,
-                 SourceLocation opLoc)
+                 SourceLocation opLoc, bool fpContractable = false)
     : Expr(BinaryOperatorClass, ResTy, VK, OK,
            lhs->isTypeDependent() || rhs->isTypeDependent(),
            lhs->isValueDependent() || rhs->isValueDependent(),

I suggest not defaulting fpContractable, so that we always have to think about it when building a new BinaryOperator.

Are there tests for the template instantiation cases?

	- Doug


> Cheers,
> Lang.
> 
> On Wed, Sep 26, 2012 at 7:50 PM, Hal Finkel <hfinkel at anl.gov> wrote:
> Lang,
> 
> Great, thanks!
> 
> Can you please add support for making a*c - b into fma(a, c, -b), etc.
> This is very important for performance on PPC (because this gets
> pattern-matched into a single instruction).
> 
>  -Hal
> 
> On Wed, 26 Sep 2012 17:12:50 -0700
> Lang Hames <lhames at gmail.com> wrote:
> 
> > Hi All,
> >
> > This patch adds support for the FP_CONTRACT pragma to clang. It adds
> > a bit to BinaryOperator and CXXOperatorCallExpr to track the
> > FP_CONTRACT pragma state as each AST node is constructed. Pragma
> > state is made to follow scope correctly by having an RAII object save
> > and restore the state when the parser encounters a new compound
> > statement body. The -ffp-contract option is tested during codegen,
> > and fmuladd intrinsics (representing fusing opportunities) are output
> > only if --ffp-contract=on.
> >
> > This patch does NOT include warnings/errors for specifying
> > FP_CONTRACT in invalid contexts that could be confusing (e.g.
> > introducing FP_CONTRACT at class scope). I think it's reasonable to
> > start by supporting valid use cases, and add restrictions/diagnostics
> > in a follow-up patch.
> >
> > Comments and feedback most welcome.
> >
> > Cheers,
> > Lang.
> 
> 
> 
> --
> Hal Finkel
> Postdoctoral Appointee
> Leadership Computing Facility
> Argonne National Laboratory
> 
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