cmd/internal/obj/riscv: support MOVD with floating point constants

Currently, we only support loading of values from memory (or other
registers). Add floating point constant support to MOVD. This is
implemented by storing the floating point constant to a symbol,
which is then loaded into the floating point register.

Change-Id: I6db242d27f606f0d5d084a3ab93538698d3a4f8c
Reviewed-on: https://go-review.googlesource.com/c/go/+/631876
Reviewed-by: Meng Zhuo <mengzhuo1203@gmail.com>
Reviewed-by: Mark Ryan <markdryan@rivosinc.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 19 insertions, 3 deletions

diff --git a/src/cmd/internal/obj/riscv/obj.go b/src/cmd/internal/obj/riscv/obj.go
index c6f66d0195..3a4ab556f7 100644
--- a/src/cmd/internal/obj/riscv/obj.go
+++ b/src/cmd/internal/obj/riscv/obj.go
@@ -147,6 +147,15 @@ func progedit(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
 			p.From.Name = obj.NAME_EXTERN
 			p.From.Offset = 0
 		}
+
+	case AMOVD:
+		if p.From.Type == obj.TYPE_FCONST && p.From.Name == obj.NAME_NONE && p.From.Reg == obj.REG_NONE {
+			f64 := p.From.Val.(float64)
+			p.From.Type = obj.TYPE_MEM
+			p.From.Sym = ctxt.Float64Sym(f64)
+			p.From.Name = obj.NAME_EXTERN
+			p.From.Offset = 0
+		}
 	}
 }
 
@@ -2322,12 +2331,19 @@ func instructionsForMOV(p *obj.Prog) []*instruction {
 			}
 
 			// Note that the values for $off_hi and $off_lo are currently
-			// zero and will be assigned during relocation.
+			// zero and will be assigned during relocation. If the destination
+			// is an integer register then we can use the same register for the
+			// address computation, otherwise we need to use the temporary register.
 			//
 			// AUIPC $off_hi, Rd
 			// L $off_lo, Rd, Rd
-			insAUIPC := &instruction{as: AAUIPC, rd: ins.rd}
-			ins.as, ins.rs1, ins.rs2, ins.imm = movToLoad(p.As), ins.rd, obj.REG_NONE, 0
+			//
+			addrReg := ins.rd
+			if addrReg < REG_X0 || addrReg > REG_X31 {
+				addrReg = REG_TMP
+			}
+			insAUIPC := &instruction{as: AAUIPC, rd: addrReg}
+			ins.as, ins.rs1, ins.rs2, ins.imm = movToLoad(p.As), addrReg, obj.REG_NONE, 0
 			inss = []*instruction{insAUIPC, ins}
 
 		default: