[15/15][Clang][RISCV][NFC] Set data member under Policy as constants

[eopXD]

Summary

The object is now correct by construction.

This is the 15th commit of a patch-set that aims to change the default policy
for RVV intrinsics from TAMU to TAMA.

Please refer to the cover letter in the 1st commit (D141573) for an
overview.

Depends on D141793.

[craig.topper]

clang/include/clang/Support/RISCVVIntrinsicUtils.h

95–96

Should this be a class instead of struct so the members are private?

[eopXD]

Update code: Address comment from Craig.

[eopXD]

Bump CI.

[craig.topper]

LGTM

[DavidSpickett]

Hi! Comparing the changes for https://lab.llvm.org/buildbot/#/builders/17/builds/33129 and https://lab.llvm.org/buildbot/#/builders/174/builds/17069 I think you've managed to hit a crash in the host compiler we (Linaro) are using for our bots. Which is the 15.0.0 release.

I will handle it, perhaps I can reduce it down to some pattern 15.x doesn't like but either way I don't think this change is at fault.

[dyung]

Hi @eopXD this change seems to be causing builds on Windows to time out for some reason. Can you take a look?

• https://lab.llvm.org/buildbot/#/builders/83/builds/28484
• https://lab.llvm.org/buildbot/#/builders/172/builds/22803
• https://lab.llvm.org/buildbot/#/builders/216/builds/16210

[eopXD]

Hi @dyung and @DavidSpickett,

Thank you for checking this out and sorry for the late reply (Chinese New Year holiday zone right now in Taiwan). Let me look into it now.

[eopXD]

Reopening the revision to try land this correctly.

[eopXD]

Rebase to latest main.

[eopXD]

This commit seems to cause riscv_vector_builtin_cg.inc to explode into a 630K file, which causes the out-of-memory build fail. Confirmed that this is the commit that is causing the error.

[DavidSpickett]

Nice!

Glad you spotted that, I have had creduce running and getting nowhere fast for a day or so. Sounds like it would never have found anything minimal.

[eopXD]

In D141796#4082665, @DavidSpickett wrote:

Nice!

Glad you spotted that, I have had creduce running and getting nowhere fast for a day or so. Sounds like it would never have found anything minimal.

Indeed! Thank you for your time again :)

[eopXD]

Update code. The removal of PolicyAttrs.IsUnspecified = false; under

void RVVIntrinsic::updateNamesAndPolicy(bool IsMasked, bool HasPolicy,
                                        std::string &Name,
                                        std::string &BuiltinName,
                                        std::string &OverloadedName,
                                        Policy &PolicyAttrs) {

/* ... */
  if (PolicyAttrs.isUnspecified()) {
  }

is incorrect becasue the == operator of the Policy object still uses it.
So repeating builtin-s were created (becasue repeating ones are not recognized
as duplicates), causing riscv_vector_builtin_cg.inc to explode.

The updated patch now only adds const qualifier to TailPolicy and
MaskPolicy.

[eopXD]

Re-commiting this now that the problem is resolved.

[DavidSpickett]

Looks good to me - https://lab.llvm.org/buildbot/#/builders/245/builds/3919

clang/include/clang/Support/RISCVVIntrinsicUtils.h

enum class TypeModifier : uint8_t {
   // However that might require VectorTypeModifier become bitmask rather than
   // simple enum, so we decide keek LMUL1 in TypeModifier for code size
   // optimization of clang binary size.
   LMUL1 = 1 << 6,
   MaxOffset = 6,
   LLVM_MARK_AS_BITMASK_ENUM(LMUL1),
 };
 
-struct Policy {
-  bool IsUnspecified = false;
+class Policy {
+public:
   enum PolicyType {
     Undisturbed,
     Agnostic,
   };
-  PolicyType TailPolicy = Agnostic;
-  PolicyType MaskPolicy = Agnostic;
+  bool IsUnspecified = false;
+
+private:
+  // The default assumption for an RVV instruction is TAMA, as an undisturbed
+  // policy generally will affect the performance of an out-of-order core.
+  const PolicyType TailPolicy = Agnostic;
+  const PolicyType MaskPolicy = Agnostic;
   bool HasTailPolicy, HasMaskPolicy;
+
+public:
   Policy(bool HasTailPolicy, bool HasMaskPolicy)
       : IsUnspecified(true), HasTailPolicy(HasTailPolicy),
         HasMaskPolicy(HasMaskPolicy) {}
   Policy(PolicyType TailPolicy, bool HasTailPolicy, bool HasMaskPolicy)
       : TailPolicy(TailPolicy), HasTailPolicy(HasTailPolicy),
         HasMaskPolicy(HasMaskPolicy) {}
   Policy(PolicyType TailPolicy, PolicyType MaskPolicy, bool HasTailPolicy,
          bool HasMaskPolicy)