On Dec 6, 2016, at 4:41 PM, Greg Parker wrote:


On Dec 6, 2016, at 7:27 AM, G 3 <programmingk...@gmail.com> wrote:

I'm working on a program that calls PowerPC assembly floating point instructions from C. It would have calls like this:

double inputA, inputB, answer;
asm volatile("fadd %0, %1, %2" : "=f" (answer) : "f" (inputA), "f" (inputB)); // answer = inputA + inputB

The odd thing is it only works in the debug configuration in XCode. In Release configuration, I see this error:
error: output constraint 0 must specify a single register
error: output operand 0 must use '&' constraint

Is there a way to fix this problem?

You'll get better answers from a clang list such as cfe- us...@lists.llvm.org. Most of the audience here probably does not have a copy of clang that can compile PowerPC code.

Why are you using constraint "f" here? I would expect you to use "d" with variables of type double.

I did a little experiment and tried this: asm volatile("fadd %0, %1, % 2" : "=f" (answer) : "d" (inputA), "f" (inputB));

It didn't work. This is the error message I saw: error: impossible constraint in 'asm'.

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