[RISCV] Define risc-v's own register class to model FP Register.

[ym1813382441]

Summary

The default RegisterClass is not enough to model RISCV Register.
We define risc-v's own register class to model FP Register.
This helps to better estimate the register pressure in the loop-vectorize.

[kito-cheng]

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h

232

Checking isHalfTy rather than isBFloatTy here, isBFloatTy is bfloat type and we don't support that in any extension yet.

[ym1813382441]

Corrected half-precision floating point.

[kito-cheng]

llvm/test/Transforms/LoopVectorize/RISCV/reg-usage.ll

22–23

Curious why there is still GPRRC here? I thought that should be FPRRC after this patch?

[ym1813382441]

llvm/test/Transforms/LoopVectorize/RISCV/reg-usage.ll

22–23

Here is the register usage after VF is selected, all float types in this loop has been changed to the vector type after vectorization.
Only Uniform and Scalar instructions after vectorization are computed into scalar registers.
The output here may not be complete enough to cause you to misunderstand.

[kito-cheng]

llvm/test/Transforms/LoopVectorize/RISCV/reg-usage.ll

22–23

Yeah, make sense, does it possible to add some testcase to show FPRRC?

[ym1813382441]

llvm/test/Transforms/LoopVectorize/RISCV/reg-usage.ll

22–23

Yeah, it's very simple. Just set VF to 1 to show FPRRC.

[ym1813382441]

Add command line to show FPRRC.

[kito-cheng]

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h

213

Checking F is enough here since Zfh and D both implied F.

[ym1813382441]

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h

213

okey

[ym1813382441]

Remove redundant conditions.

[kito-cheng]

LGTM

[frasercrmck]

Just some nits from me

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h

213

Nit but with V we have a ternary but here we have an if/else (of sorts)

Maybe they should be consistent?

224

Blank line between functions

239

Unnecessary semicolon. Also blank line between functions

[ym1813382441]

In D126854#3559588, @frasercrmck wrote:

Just some nits from me

Sorry I didn't notice. I have submitted it.

[kito-cheng]

Sorry I didn't notice. I have submitted it.

You could create another NFC patch to address @frasercrmck's comment :)

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h

public:
   }
 
   unsigned getMaxInterleaveFactor(unsigned VF) {
     // If the loop will not be vectorized, don't interleave the loop.
     // Let regular unroll to unroll the loop.
     return VF == 1 ? 1 : ST->getMaxInterleaveFactor();
   }
 
-  // TODO: We should define RISC-V's own register classes.
-  //       e.g. register class for FPR.
+  enum RISCVRegisterClass { GPRRC, FPRRC, VRRC };
   unsigned getNumberOfRegisters(unsigned ClassID) const {
-    bool Vector = (ClassID == 1);
-    if (Vector) {
-      if (ST->hasVInstructions())
-        return 32;
-      return 0;
-    }
+    switch (ClassID) {
+    case RISCVRegisterClass::GPRRC:
       // 31 = 32 GPR - x0 (zero register)
       // FIXME: Should we exclude fixed registers like SP, TP or GP?
       return 31;
+    case RISCVRegisterClass::FPRRC:
+      if (ST->hasStdExtZfh() || ST->hasStdExtF() || ST->hasStdExtD())
+        return 32;
+      return 0;
+    case RISCVRegisterClass::VRRC:
+      // Although there are 32 vector registers, v0 is special in that it is the
+      // only register that can be used to hold a mask.
+      // FIXME: Should we conservatively return 31 as the number of usable
+      // vector registers?
+      return ST->hasVInstructions() ? 32 : 0;
+    }
+    llvm_unreachable("unknown register class");
+  }
+  unsigned getRegisterClassForType(bool Vector, Type *Ty = nullptr) const {
+    if (Vector)
+      return RISCVRegisterClass::VRRC;
+    if (!Ty)
+      return RISCVRegisterClass::GPRRC;
+
+    Type *ScalarTy = Ty->getScalarType();
+    if ((ScalarTy->isBFloatTy() && ST->hasStdExtZfh()) ||
+        (ScalarTy->isFloatTy() && ST->hasStdExtF()) ||
+        (ScalarTy->isDoubleTy() && ST->hasStdExtD())) {
+      return RISCVRegisterClass::FPRRC;
+    }
+
+    return RISCVRegisterClass::GPRRC;
+  };
+  const char *getRegisterClassName(unsigned ClassID) const {
+    switch (ClassID) {
+    case RISCVRegisterClass::GPRRC:
+      return "RISCV::GPRRC";
+    case RISCVRegisterClass::FPRRC:
+      return "RISCV::FPRRC";
+    case RISCVRegisterClass::VRRC:
+      return "RISCV::VRRC";
+    }
+    llvm_unreachable("unknown register class");
   }
 };
 
 } // end namespace llvm
 
 #endif // LLVM_LIB_TARGET_RISCV_RISCVTARGETTRANSFORMINFO_H

llvm/test/Transforms/LoopVectorize/RISCV/reg-usage.ll

 ; RUN: opt -loop-vectorize -mtriple riscv64-linux-gnu \
 ; RUN:   -mattr=+v,+d -debug-only=loop-vectorize \
 ; RUN:   -riscv-v-vector-bits-min=128 -riscv-v-register-bit-width-lmul=8 \
 ; RUN:   -S < %s 2>&1 | FileCheck %s --check-prefix=CHECK-LMUL8
 
 define void @add(float* noalias nocapture readonly %src1, float* noalias nocapture readonly %src2, i32 signext %size, float* noalias nocapture writeonly %result) {
 ; CHECK-LABEL: add
 ; CHECK-LMUL1:      LV(REG): Found max usage: 2 item
-; CHECK-LMUL1-NEXT: LV(REG): RegisterClass: Generic::ScalarRC, 2 registers
-; CHECK-LMUL1-NEXT: LV(REG): RegisterClass: Generic::VectorRC, 2 registers
+; CHECK-LMUL1-NEXT: LV(REG): RegisterClass: RISCV::GPRRC, 2 registers
+; CHECK-LMUL1-NEXT: LV(REG): RegisterClass: RISCV::VRRC, 2 registers
 ; CHECK-LMUL1-NEXT: LV(REG): Found invariant usage: 1 item
-; CHECK-LMUL1-NEXT: LV(REG): RegisterClass: Generic::VectorRC, 2 registers
+; CHECK-LMUL1-NEXT: LV(REG): RegisterClass: RISCV::VRRC, 2 registers
 ; CHECK-LMUL2:      LV(REG): Found max usage: 2 item
-; CHECK-LMUL2-NEXT: LV(REG): RegisterClass: Generic::ScalarRC, 2 registers
-; CHECK-LMUL2-NEXT: LV(REG): RegisterClass: Generic::VectorRC, 4 registers
+; CHECK-LMUL2-NEXT: LV(REG): RegisterClass: RISCV::GPRRC, 2 registers
+; CHECK-LMUL2-NEXT: LV(REG): RegisterClass: RISCV::VRRC, 4 registers
 ; CHECK-LMUL2-NEXT: LV(REG): Found invariant usage: 1 item
-; CHECK-LMUL2-NEXT: LV(REG): RegisterClass: Generic::VectorRC, 4 registers
+; CHECK-LMUL2-NEXT: LV(REG): RegisterClass: RISCV::VRRC, 4 registers
 ; CHECK-LMUL4:      LV(REG): Found max usage: 2 item
-; CHECK-LMUL4-NEXT: LV(REG): RegisterClass: Generic::ScalarRC, 2 registers
-; CHECK-LMUL4-NEXT: LV(REG): RegisterClass: Generic::VectorRC, 8 registers
+; CHECK-LMUL4-NEXT: LV(REG): RegisterClass: RISCV::GPRRC, 2 registers
+; CHECK-LMUL4-NEXT: LV(REG): RegisterClass: RISCV::VRRC, 8 registers
 ; CHECK-LMUL4-NEXT: LV(REG): Found invariant usage: 1 item
-; CHECK-LMUL4-NEXT: LV(REG): RegisterClass: Generic::VectorRC, 8 registers
+; CHECK-LMUL4-NEXT: LV(REG): RegisterClass: RISCV::VRRC, 8 registers
 ; CHECK-LMUL8:      LV(REG): Found max usage: 2 item
-; CHECK-LMUL8-NEXT: LV(REG): RegisterClass: Generic::ScalarRC, 2 registers
-; CHECK-LMUL8-NEXT: LV(REG): RegisterClass: Generic::VectorRC, 16 registers
+; CHECK-LMUL8-NEXT: LV(REG): RegisterClass: RISCV::GPRRC, 2 registers
+; CHECK-LMUL8-NEXT: LV(REG): RegisterClass: RISCV::VRRC, 16 registers
 ; CHECK-LMUL8-NEXT: LV(REG): Found invariant usage: 1 item
-; CHECK-LMUL8-NEXT: LV(REG): RegisterClass: Generic::VectorRC, 16 registers
+; CHECK-LMUL8-NEXT: LV(REG): RegisterClass: RISCV::VRRC, 16 registers
 
 entry:
   %conv = zext i32 %size to i64
   %cmp10.not = icmp eq i32 %size, 0
   br i1 %cmp10.not, label %for.cond.cleanup, label %for.body
 
 for.cond.cleanup:
   ret void