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

[Xiaolin Zheng]

> 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

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10867/files
  - new: https://git.openjdk.org/jdk/pull/10867/files/01e54b45..9334ce71

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10867&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10867&range=02-03

  Stats: 9 lines in 1 file changed: 0 ins; 9 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10867.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10867/head:pull/10867

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