RFR: 8308340: C2: Idealize Fma nodes [v5]

[Fei Gao]

> Some platforms, like aarch64, ppc, and riscv, support fusing `Math.fma(-a, b, c)` or `Math.fma(a, -b, c)` by generating partially symmetric match rules like:
> 
> 
>   match(Set dst (FmaF src3 (Binary (NegF src1) src2)));
>   match(Set dst (FmaF src3 (Binary src1 (NegF src2))));
> 
> 
> Since `Fma` is partially commutative, the patch is to convert `Math.fma(-a, b, c)` to `Math.fma(b, -a, c)` in gvn phase, making node patterns canonical. Then we can remove redundant rules.
> 
> Also, we should guarantee that C2 generates `Fma` nodes only on platforms supporting `Fma` instructions before matcher, so we can remove all `predicate(UseFMA)` for all `Fma` rules.
> 
> After the patch, the code size of libjvm.so on aarch64 platform decreased by 63.4k.
> 
> The patch passed all tier 1 - 3 on aarch64 and x86 platforms.

Fei Gao has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains six commits:

 - Merge branch 'master' into fg8308340
 - Merge branch 'master' into fg8308340
 - Merge branch 'master' into fg8308340
 - Move check for UseFMA from c2compiler.cpp to Matcher::match_rule_supported in .ad files
 - Merge branch 'master' into fg8308340
 - 8308340: C2: Idealize Fma nodes
   
   Some platforms, like aarch64, ppc, and riscv, support fusing
   `Math.fma(-a, b, c)` or `Math.fma(a, -b, c)` by generating
   partially symmetric match rules like:
   
   ```
     match(Set dst (FmaF src3 (Binary (NegF src1) src2)));
     match(Set dst (FmaF src3 (Binary src1 (NegF src2))));
   ```
   
   Since `Fma` is partially communitive, the patch is to convert
   `Math.fma(-a, b, c)` to `Math.fma(b, -a, c)` in gvn phase,
   making node patterns canonical. Then we can remove redundant
   rules.
   
   Also, we should guarantee that C2 generates `Fma` nodes only on
   platforms supporting `Fma` instructions before matcher, so we
   can remove all `predicate(UseFMA)` for all `Fma` rules.
   
   After the patch, the code size of libjvm.so on aarch64 platform
   decreased by 63.4k.
   
   The patch passed all tier 1 - 3 on aarch64 and x86 platforms.

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

Changes: https://git.openjdk.org/jdk/pull/14576/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14576&range=04
  Stats: 608 lines in 20 files changed: 389 ins; 118 del; 101 mod
  Patch: https://git.openjdk.org/jdk/pull/14576.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14576/head:pull/14576

PR: https://git.openjdk.org/jdk/pull/14576