[llvm] r183854 - [PowerPC] Fix switch warnings from r183841.

[David Blaikie]

On Wed, Jun 12, 2013 at 12:20 PM, Bill Schmidt
<wschmidt at linux.vnet.ibm.com> wrote:
> Author: wschmidt
> Date: Wed Jun 12 14:20:32 2013
> New Revision: 183854
>
> URL: http://llvm.org/viewvc/llvm-project?rev=183854&view=rev
> Log:
> [PowerPC] Fix switch warnings from r183841.
>
> Introducing PRED_BAD caused some unexpected warnings that are now
> suppressed.
>
> Modified:
>     llvm/trunk/lib/Target/PowerPC/InstPrinter/PPCInstPrinter.cpp
>     llvm/trunk/lib/Target/PowerPC/MCTargetDesc/PPCPredicates.cpp
>
> Modified: llvm/trunk/lib/Target/PowerPC/InstPrinter/PPCInstPrinter.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/InstPrinter/PPCInstPrinter.cpp?rev=183854&r1=183853&r2=183854&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/PowerPC/InstPrinter/PPCInstPrinter.cpp (original)
> +++ llvm/trunk/lib/Target/PowerPC/InstPrinter/PPCInstPrinter.cpp Wed Jun 12 14:20:32 2013
> @@ -90,6 +90,7 @@ void PPCInstPrinter::printPredicateOpera
>
>    if (StringRef(Modifier) == "cc") {
>      switch ((PPC::Predicate)Code) {
> +    default: llvm_unreachable("Bad predicate!");

I've reverted this change (now that you've removed PRED_BAD) in
r183863 due to -Werror build break from -Wcovered-switch-default.

Generally we try not to put default cases in fully covered switches
(indeed -Wcovered-switch-default ensures we never do this) so that
-Wswitch-enum can properly warn us when we add a new enum element &
need to consider how it's handled in each pre-existing switch.

It would've been preferable for your fix here to have been adding the
specific case with a separate unreachable (or nothing, so as to fall
through to the unreachable at the end) so that other non-BAD values
added to the enum would've still produced warnings in these switches
to help the developer update the cases that would need to handle them.

Thanks!
- David

>      case PPC::PRED_LT: O << "lt"; return;
>      case PPC::PRED_LE: O << "le"; return;
>      case PPC::PRED_EQ: O << "eq"; return;
>
> Modified: llvm/trunk/lib/Target/PowerPC/MCTargetDesc/PPCPredicates.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/MCTargetDesc/PPCPredicates.cpp?rev=183854&r1=183853&r2=183854&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/PowerPC/MCTargetDesc/PPCPredicates.cpp (original)
> +++ llvm/trunk/lib/Target/PowerPC/MCTargetDesc/PPCPredicates.cpp Wed Jun 12 14:20:32 2013
> @@ -18,6 +18,7 @@ using namespace llvm;
>
>  PPC::Predicate PPC::InvertPredicate(PPC::Predicate Opcode) {
>    switch (Opcode) {
> +  default: llvm_unreachable("Unknown PPC branch opcode!");
>    case PPC::PRED_EQ: return PPC::PRED_NE;
>    case PPC::PRED_NE: return PPC::PRED_EQ;
>    case PPC::PRED_LT: return PPC::PRED_GE;
> @@ -27,11 +28,11 @@ PPC::Predicate PPC::InvertPredicate(PPC:
>    case PPC::PRED_NU: return PPC::PRED_UN;
>    case PPC::PRED_UN: return PPC::PRED_NU;
>    }
> -  llvm_unreachable("Unknown PPC branch opcode!");
>  }
>
>  PPC::Predicate PPC::getSwappedPredicate(PPC::Predicate Opcode) {
>    switch (Opcode) {
> +  default: llvm_unreachable("Unknown PPC branch opcode!");
>    case PPC::PRED_EQ: return PPC::PRED_EQ;
>    case PPC::PRED_NE: return PPC::PRED_NE;
>    case PPC::PRED_LT: return PPC::PRED_GT;
> @@ -41,6 +42,5 @@ PPC::Predicate PPC::getSwappedPredicate(
>    case PPC::PRED_NU: return PPC::PRED_NU;
>    case PPC::PRED_UN: return PPC::PRED_UN;
>    }
> -  llvm_unreachable("Unknown PPC branch opcode!");
>  }
>
>
>
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