[dev.ssa] cmd/compile: fix fp constant loads for 386+PIC

In position-independent 386 code, loading floating-point constants from
the constant pool requires two steps: materializing the address of
the constant pool entry (requires calling a thunk) and then loading
from that address.

Before this CL, the materializing happened implicitly in CX, which
clobbered that register.

Change-Id: Id094e0fb2d3be211089f299e8f7c89c315de0a87
Reviewed-on: https://go-review.googlesource.com/26811
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

6 files changed, 196 insertions, 26 deletions

diff --git a/src/cmd/compile/internal/ssa/gen/386.rules b/src/cmd/compile/internal/ssa/gen/386.rules
index b360189e43..0609d3b24a 100644
--- a/src/cmd/compile/internal/ssa/gen/386.rules
+++ b/src/cmd/compile/internal/ssa/gen/386.rules
@@ -70,8 +70,10 @@
 (Neg32  x) -> (NEGL x)
 (Neg16  x) -> (NEGL x)
 (Neg8   x) -> (NEGL x)
-(Neg32F x) -> (PXOR x (MOVSSconst <config.Frontend().TypeFloat32()> [f2i(math.Copysign(0, -1))]))
-(Neg64F x) -> (PXOR x (MOVSDconst <config.Frontend().TypeFloat64()> [f2i(math.Copysign(0, -1))]))
+(Neg32F x) && !config.use387 -> (PXOR x (MOVSSconst <config.Frontend().TypeFloat32()> [f2i(math.Copysign(0, -1))]))
+(Neg64F x) && !config.use387 -> (PXOR x (MOVSDconst <config.Frontend().TypeFloat64()> [f2i(math.Copysign(0, -1))]))
+(Neg32F x) && config.use387 -> (FCHS x)
+(Neg64F x) && config.use387 -> (FCHS x)
 
 (Com32 x) -> (NOTL x)
 (Com16 x) -> (NOTL x)
@@ -1250,3 +1252,8 @@
   && x.Uses == 1
   && clobber(x)
   -> (MOVLstoreidx1 [i-2] {s} p (SHLLconst <idx.Type> [1] idx) w0 mem)
+
+// For PIC, break floating-point constant loading into two instructions so we have
+// a register to use for holding the address of the constant pool entry.
+(MOVSSconst [c]) && config.ctxt.Flag_shared -> (MOVSSconst2 (MOVSSconst1 [c]))
+(MOVSDconst [c]) && config.ctxt.Flag_shared -> (MOVSDconst2 (MOVSDconst1 [c]))
diff --git a/src/cmd/compile/internal/ssa/gen/386Ops.go b/src/cmd/compile/internal/ssa/gen/386Ops.go
index 86f6f72370..1013adf4a6 100644
--- a/src/cmd/compile/internal/ssa/gen/386Ops.go
+++ b/src/cmd/compile/internal/ssa/gen/386Ops.go
@@ -463,6 +463,18 @@ func init() {
 		{name: "FlagLT_UGT"}, // signed < and unsigned >
 		{name: "FlagGT_UGT"}, // signed > and unsigned <
 		{name: "FlagGT_ULT"}, // signed > and unsigned >
+
+		// Special op for -x on 387
+		{name: "FCHS", argLength: 1, reg: fp11},
+
+		// Special ops for PIC floating-point constants.
+		// MOVSXconst1 loads the address of the constant-pool entry into a register.
+		// MOVSXconst2 loads the constant from that address.
+		// MOVSXconst1 returns a pointer, but we type it as uint32 because it can never point to the Go heap.
+		{name: "MOVSSconst1", reg: gp01, typ: "UInt32", aux: "Float32"},
+		{name: "MOVSDconst1", reg: gp01, typ: "UInt32", aux: "Float64"},
+		{name: "MOVSSconst2", argLength: 1, reg: gpfp, asm: "MOVSS"},
+		{name: "MOVSDconst2", argLength: 1, reg: gpfp, asm: "MOVSD"},
 	}
 
 	var _386blocks = []blockData{
diff --git a/src/cmd/compile/internal/ssa/opGen.go b/src/cmd/compile/internal/ssa/opGen.go
index 38a2ba7136..75381c4246 100644
--- a/src/cmd/compile/internal/ssa/opGen.go
+++ b/src/cmd/compile/internal/ssa/opGen.go
@@ -345,6 +345,11 @@ const (
 	Op386FlagLT_UGT
 	Op386FlagGT_UGT
 	Op386FlagGT_ULT
+	Op386FCHS
+	Op386MOVSSconst1
+	Op386MOVSDconst1
+	Op386MOVSSconst2
+	Op386MOVSDconst2
 
 	OpAMD64ADDSS
 	OpAMD64ADDSD
@@ -3675,6 +3680,64 @@ var opcodeTable = [...]opInfo{
 		argLen: 0,
 		reg:    regInfo{},
 	},
+	{
+		name:   "FCHS",
+		argLen: 1,
+		reg: regInfo{
+			inputs: []inputInfo{
+				{0, 65280}, // X0 X1 X2 X3 X4 X5 X6 X7
+			},
+			outputs: []outputInfo{
+				{0, 65280}, // X0 X1 X2 X3 X4 X5 X6 X7
+			},
+		},
+	},
+	{
+		name:    "MOVSSconst1",
+		auxType: auxFloat32,
+		argLen:  0,
+		reg: regInfo{
+			outputs: []outputInfo{
+				{0, 239}, // AX CX DX BX BP SI DI
+			},
+		},
+	},
+	{
+		name:    "MOVSDconst1",
+		auxType: auxFloat64,
+		argLen:  0,
+		reg: regInfo{
+			outputs: []outputInfo{
+				{0, 239}, // AX CX DX BX BP SI DI
+			},
+		},
+	},
+	{
+		name:   "MOVSSconst2",
+		argLen: 1,
+		asm:    x86.AMOVSS,
+		reg: regInfo{
+			inputs: []inputInfo{
+				{0, 239}, // AX CX DX BX BP SI DI
+			},
+			outputs: []outputInfo{
+				{0, 65280}, // X0 X1 X2 X3 X4 X5 X6 X7
+			},
+		},
+	},
+	{
+		name:   "MOVSDconst2",
+		argLen: 1,
+		asm:    x86.AMOVSD,
+		reg: regInfo{
+			inputs: []inputInfo{
+				{0, 239}, // AX CX DX BX BP SI DI
+			},
+			outputs: []outputInfo{
+				{0, 65280}, // X0 X1 X2 X3 X4 X5 X6 X7
+			},
+		},
+	},
 
 	{
 		name:         "ADDSS",
diff --git a/src/cmd/compile/internal/ssa/rewrite386.go b/src/cmd/compile/internal/ssa/rewrite386.go
index caccf88b7a..b791c44098 100644
--- a/src/cmd/compile/internal/ssa/rewrite386.go
+++ b/src/cmd/compile/internal/ssa/rewrite386.go
@@ -78,6 +78,8 @@ func rewriteValue386(v *Value, config *Config) bool {
 		return rewriteValue386_Op386MOVLstoreidx1(v, config)
 	case Op386MOVLstoreidx4:
 		return rewriteValue386_Op386MOVLstoreidx4(v, config)
+	case Op386MOVSDconst:
+		return rewriteValue386_Op386MOVSDconst(v, config)
 	case Op386MOVSDload:
 		return rewriteValue386_Op386MOVSDload(v, config)
 	case Op386MOVSDloadidx1:
@@ -90,6 +92,8 @@ func rewriteValue386(v *Value, config *Config) bool {
 		return rewriteValue386_Op386MOVSDstoreidx1(v, config)
 	case Op386MOVSDstoreidx8:
 		return rewriteValue386_Op386MOVSDstoreidx8(v, config)
+	case Op386MOVSSconst:
+		return rewriteValue386_Op386MOVSSconst(v, config)
 	case Op386MOVSSload:
 		return rewriteValue386_Op386MOVSSload(v, config)
 	case Op386MOVSSloadidx1:
@@ -4213,6 +4217,25 @@ func rewriteValue386_Op386MOVLstoreidx4(v *Value, config *Config) bool {
 	}
 	return false
 }
+func rewriteValue386_Op386MOVSDconst(v *Value, config *Config) bool {
+	b := v.Block
+	_ = b
+	// match: (MOVSDconst [c])
+	// cond: config.ctxt.Flag_shared
+	// result: (MOVSDconst2 (MOVSDconst1 [c]))
+	for {
+		c := v.AuxInt
+		if !(config.ctxt.Flag_shared) {
+			break
+		}
+		v.reset(Op386MOVSDconst2)
+		v0 := b.NewValue0(v.Line, Op386MOVSDconst1, config.fe.TypeUInt32())
+		v0.AuxInt = c
+		v.AddArg(v0)
+		return true
+	}
+	return false
+}
 func rewriteValue386_Op386MOVSDload(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
@@ -4683,6 +4706,25 @@ func rewriteValue386_Op386MOVSDstoreidx8(v *Value, config *Config) bool {
 	}
 	return false
 }
+func rewriteValue386_Op386MOVSSconst(v *Value, config *Config) bool {
+	b := v.Block
+	_ = b
+	// match: (MOVSSconst [c])
+	// cond: config.ctxt.Flag_shared
+	// result: (MOVSSconst2 (MOVSSconst1 [c]))
+	for {
+		c := v.AuxInt
+		if !(config.ctxt.Flag_shared) {
+			break
+		}
+		v.reset(Op386MOVSSconst2)
+		v0 := b.NewValue0(v.Line, Op386MOVSSconst1, config.fe.TypeUInt32())
+		v0.AuxInt = c
+		v.AddArg(v0)
+		return true
+	}
+	return false
+}
 func rewriteValue386_Op386MOVSSload(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
@@ -11399,10 +11441,13 @@ func rewriteValue386_OpNeg32F(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
 	// match: (Neg32F x)
-	// cond:
+	// cond: !config.use387
 	// result: (PXOR x (MOVSSconst <config.Frontend().TypeFloat32()> [f2i(math.Copysign(0, -1))]))
 	for {
 		x := v.Args[0]
+		if !(!config.use387) {
+			break
+		}
 		v.reset(Op386PXOR)
 		v.AddArg(x)
 		v0 := b.NewValue0(v.Line, Op386MOVSSconst, config.Frontend().TypeFloat32())
@@ -11410,15 +11455,31 @@ func rewriteValue386_OpNeg32F(v *Value, config *Config) bool {
 		v.AddArg(v0)
 		return true
 	}
+	// match: (Neg32F x)
+	// cond: config.use387
+	// result: (FCHS x)
+	for {
+		x := v.Args[0]
+		if !(config.use387) {
+			break
+		}
+		v.reset(Op386FCHS)
+		v.AddArg(x)
+		return true
+	}
+	return false
 }
 func rewriteValue386_OpNeg64F(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
 	// match: (Neg64F x)
-	// cond:
+	// cond: !config.use387
 	// result: (PXOR x (MOVSDconst <config.Frontend().TypeFloat64()> [f2i(math.Copysign(0, -1))]))
 	for {
 		x := v.Args[0]
+		if !(!config.use387) {
+			break
+		}
 		v.reset(Op386PXOR)
 		v.AddArg(x)
 		v0 := b.NewValue0(v.Line, Op386MOVSDconst, config.Frontend().TypeFloat64())
@@ -11426,6 +11487,19 @@ func rewriteValue386_OpNeg64F(v *Value, config *Config) bool {
 		v.AddArg(v0)
 		return true
 	}
+	// match: (Neg64F x)
+	// cond: config.use387
+	// result: (FCHS x)
+	for {
+		x := v.Args[0]
+		if !(config.use387) {
+			break
+		}
+		v.reset(Op386FCHS)
+		v.AddArg(x)
+		return true
+	}
+	return false
 }
 func rewriteValue386_OpNeg8(v *Value, config *Config) bool {
 	b := v.Block
diff --git a/src/cmd/compile/internal/x86/387.go b/src/cmd/compile/internal/x86/387.go
index 96a7d63082..bd0971cf4e 100644
--- a/src/cmd/compile/internal/x86/387.go
+++ b/src/cmd/compile/internal/x86/387.go
@@ -29,6 +29,14 @@ func ssaGenValue387(s *gc.SSAGenState, v *ssa.Value) bool {
 		p.To.Reg = x86.REG_F0
 		popAndSave(s, v)
 		return true
+	case ssa.Op386MOVSSconst2, ssa.Op386MOVSDconst2:
+		p := gc.Prog(loadPush(v.Type))
+		p.From.Type = obj.TYPE_MEM
+		p.From.Reg = gc.SSARegNum(v.Args[0])
+		p.To.Type = obj.TYPE_REG
+		p.To.Reg = x86.REG_F0
+		popAndSave(s, v)
+		return true
 
 	case ssa.Op386MOVSSload, ssa.Op386MOVSDload, ssa.Op386MOVSSloadidx1, ssa.Op386MOVSDloadidx1, ssa.Op386MOVSSloadidx4, ssa.Op386MOVSDloadidx8:
 		p := gc.Prog(loadPush(v.Type))
@@ -183,28 +191,11 @@ func ssaGenValue387(s *gc.SSAGenState, v *ssa.Value) bool {
 		popAndSave(s, v)
 		return true
 
-	case ssa.Op386PXOR:
-		a0 := v.Args[0]
-		a1 := v.Args[1]
-		for a0.Op == ssa.OpCopy {
-			a0 = a0.Args[0]
-		}
-		for a1.Op == ssa.OpCopy {
-			a1 = a1.Args[0]
-		}
-		if (a0.Op == ssa.Op386MOVSSconst || a0.Op == ssa.Op386MOVSDconst) && a0.AuxInt == -0x8000000000000000 {
-			push(s, v.Args[1])
-			gc.Prog(x86.AFCHS)
-			popAndSave(s, v)
-			return true
-		}
-		if (a1.Op == ssa.Op386MOVSSconst || a1.Op == ssa.Op386MOVSDconst) && a1.AuxInt == -0x8000000000000000 {
-			push(s, v.Args[0])
-			gc.Prog(x86.AFCHS)
-			popAndSave(s, v)
-			return true
-		}
-		v.Fatalf("PXOR not used to change sign %s", v.LongString())
+	case ssa.Op386FCHS:
+		push(s, v.Args[0])
+		gc.Prog(x86.AFCHS)
+		popAndSave(s, v)
+		return true
 
 	case ssa.Op386CVTSL2SS, ssa.Op386CVTSL2SD:
 		p := gc.Prog(x86.AMOVL)
diff --git a/src/cmd/compile/internal/x86/ssa.go b/src/cmd/compile/internal/x86/ssa.go
index e941e6cda7..3005a19bfd 100644
--- a/src/cmd/compile/internal/x86/ssa.go
+++ b/src/cmd/compile/internal/x86/ssa.go
@@ -456,6 +456,27 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		p.From.Val = math.Float64frombits(uint64(v.AuxInt))
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = x
+	case ssa.Op386MOVSSconst1, ssa.Op386MOVSDconst1:
+		var literal string
+		if v.Op == ssa.Op386MOVSDconst1 {
+			literal = fmt.Sprintf("$f64.%016x", uint64(v.AuxInt))
+		} else {
+			literal = fmt.Sprintf("$f32.%08x", math.Float32bits(float32(math.Float64frombits(uint64(v.AuxInt)))))
+		}
+		p := gc.Prog(x86.ALEAL)
+		p.From.Type = obj.TYPE_MEM
+		p.From.Name = obj.NAME_EXTERN
+		p.From.Sym = obj.Linklookup(gc.Ctxt, literal, 0)
+		p.From.Sym.Local = true
+		p.To.Type = obj.TYPE_REG
+		p.To.Reg = gc.SSARegNum(v)
+	case ssa.Op386MOVSSconst2, ssa.Op386MOVSDconst2:
+		p := gc.Prog(v.Op.Asm())
+		p.From.Type = obj.TYPE_MEM
+		p.From.Reg = gc.SSARegNum(v.Args[0])
+		p.To.Type = obj.TYPE_REG
+		p.To.Reg = gc.SSARegNum(v)
+
 	case ssa.Op386MOVSSload, ssa.Op386MOVSDload, ssa.Op386MOVLload, ssa.Op386MOVWload, ssa.Op386MOVBload, ssa.Op386MOVBLSXload, ssa.Op386MOVWLSXload:
 		p := gc.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_MEM
@@ -872,6 +893,8 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		if gc.Debug_checknil != 0 && v.Line > 1 { // v.Line==1 in generated wrappers
 			gc.Warnl(v.Line, "generated nil check")
 		}
+	case ssa.Op386FCHS:
+		v.Fatalf("FCHS in non-387 mode")
 	default:
 		v.Unimplementedf("genValue not implemented: %s", v.LongString())
 	}