RFR(M): 7133857: exp() and pow() should use the x87 ISA on x86

[Vladimir Kozlov]

Looks good. It would be nice if you put this explanation into the 
MacroAssembler::pow_or_exp() code as comment.

It is also not clear who set stack in case y_not_huge:

+    jcc(Assembler::notEqual, y_not_huge);
+
+    movl(Address(rsp, 0), 0);
+    movl(Address(rsp, 4), 0);
+
+    bind(y_not_huge);
...

+    pop(tmp2);
+    NOT_LP64(pop(tmp3));

Vladimir

Roland Westrelin wrote:
>> That looks good.  Did you run the PowTests.java regression test from 
>> the JDK for all the configurations?
> 
> I found a couple problems when I ran this test on x86 so here is a new 
> webrev:
> 
> http://cr.openjdk.java.net/~roland/7133857/webrev.02/
> 
> With c1, this code was missing:
> 
> diff --git a/src/cpu/x86/vm/c1_LIRGenerator_x86.cpp 
> b/src/cpu/x86/vm/c1_LIRGenerator_x86.cpp
> --- a/src/cpu/x86/vm/c1_LIRGenerator_x86.cpp
> +++ b/src/cpu/x86/vm/c1_LIRGenerator_x86.cpp
> @@ -848,6 +848,10 @@
>    LIR_Opr calc_input2 = NULL;
>    if (x->id() == vmIntrinsics::_dpow) {
>      LIRItem extra_arg(x->argument_at(1), this);
> +    if (UseSSE < 2) {
> +      extra_arg.set_destroys_register();
> +    }
> +    extra_arg.load_item();
>      calc_input2 = extra_arg.result();
>    }
>    LIR_Opr calc_result = rlock_result(x);
> 
> 
> Also one corner case was not well handled by the interpreter/c1 assembly 
> code. For x^y, when x < 0, y has to be an integer and we need to test 
> whether it's odd or even. The previous code would fallback to the 
> runtime code if y was too large for a 32 bit integer. So for instance 
> Math.pow(x,y) with x < 0 and a large y would be computed by the C code 
> but Math.pow(-x, y) which should be +/- Math.pow(x, y) depending on y's 
> parity would be computed by the assembly code and results would differ. 
> So on the x < 0 code path, I now check for y+1 == y which is true for 
> very large numbers that are all odd and if the test fails I use a 64 bit 
> rather than a 32 bit integer which is guaranteed to not overflow for 
> numbers where y+1 != y.
> 
> Roland.