RFR: 8295926: RISC-V: C1: Fix LIRGenerator::do_LibmIntrinsic [v4]

[Fei Yang]

On Fri, 28 Oct 2022 03:53:27 GMT, Xiaolin Zheng <xlinzheng at openjdk.org> wrote:

>> The ported logic of LIRGenerator::do_LibmIntrinsic has a correctness problem, which will kill argument registers when the current libm intrinsic's operand is also a libm intrinsic, such as:
>> 
>> (dpow val1 (dlog val2))
>> 
>> LIRItem walks operands, so the `value.load_item_force(cc->at(0));` should be moved below after the LIRItem, or the result of `cc->at(0)` would be killed. But we might as well keep aligning AArch64's style to reduce some maintenance work.
>> 
>> 
>> Reproducer:
>> 
>> 
>> public class A {
>> 
>>     static int count = 0;
>> 
>>     public static void print(double var) {
>>         if (count % 10000 == 0) {
>>             System.out.println(var);
>>         }
>>         count++;
>>     }
>> 
>>     public static void a(double var1, double var2, double var3) {
>>         double var4 = Math.pow(var3, Math.log(var1 / var2));
>>         print(var4);
>>     }
>> 
>>     public static void main(String[] args) {
>> 
>>         for (int i = 0; i < 50000; i++) {
>>             double var21 = 2.2250738585072014E-308D;
>>             double var15 = 1.1102230246251565E-16D;
>>             double d1 = 2.0D;
>>             A.a(var21, var15, d1);
>>         }
>> 
>>     }
>> 
>> }
>> 
>> 
>> The right answer is
>> 
>> 6.461124611136231E-203
>> 6.461124611136231E-203
>> 6.461124611136231E-203
>> 6.461124611136231E-203
>> 6.461124611136231E-203
>> 
>> 
>> The current backend gives
>> 
>> 6.461124611136231E-203
>> NaN
>> NaN
>> NaN
>> NaN
>> 
>> 
>> Testing a hotspot tier1~4 on qemu.
>> 
>> Thanks,
>> Xiaolin
>
> Xiaolin Zheng has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix the newly-added test

Updated change looks good. Thanks for finding and fixing this.

-------------

Marked as reviewed by fyang (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10867