[dev.ssa] cmd/compile: small improvements

Found looking at mapaccess1_faststr.

runtime.throw never returns.
Do x+y+c with an LEA.

Change-Id: I27ea6669324242a6302397cbdc73230891d97591
Reviewed-on: https://go-review.googlesource.com/19911
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/gc/ssa.go

@@ -544,8 +544,9 @@ func (s *state) stmt(n *Node) {
 	// Expression statements
 	case OCALLFUNC, OCALLMETH, OCALLINTER:
 		s.call(n, callNormal)
-		if n.Op == OCALLFUNC && n.Left.Op == ONAME && n.Left.Class == PFUNC && n.Left.Sym.Pkg == Runtimepkg &&
-			(n.Left.Sym.Name == "gopanic" || n.Left.Sym.Name == "selectgo") {
+		if n.Op == OCALLFUNC && n.Left.Op == ONAME && n.Left.Class == PFUNC &&
+			(compiling_runtime != 0 && n.Left.Sym.Name == "throw" ||
+				n.Left.Sym.Pkg == Runtimepkg && (n.Left.Sym.Name == "gopanic" || n.Left.Sym.Name == "selectgo")) {
 			m := s.mem()
 			b := s.endBlock()
 			b.Kind = ssa.BlockExit

src/cmd/compile/internal/ssa/TODO

@@ -34,6 +34,14 @@ Optimizations (better compiled code)
   flag regeneration.
 - In forms like if ... { call } else { no call }, mark the call branch as unlikely.
 - Non-constant rotate detection.
+- Do 0 <= x && x < n with one unsigned compare
+- nil-check removal in indexed load/store case:
+    lea    (%rdx,%rax,1),%rcx
+    test   %al,(%rcx)           // nil check
+    mov    (%rdx,%rax,1),%cl    // load to same address
+- any pointer generated by unsafe arithmetic must be non-nil?
+  (Of course that may not be true in general, but it is for all uses
+   in the runtime, and we can play games with unsafe.)
 
 Optimizations (better compiler)
 -------------------------------

src/cmd/compile/internal/ssa/gen/AMD64.rules

@@ -558,6 +558,11 @@
 (ADDQ x (ADDQ x y)) -> (LEAQ2 y x)
 (ADDQ x (ADDQ y x)) -> (LEAQ2 y x)
 
+// combine ADDQ/ADDQconst into LEAQ1
+(ADDQconst [c] (ADDQ x y)) -> (LEAQ1 [c] x y)
+(ADDQ (ADDQconst [c] x) y) -> (LEAQ1 [c] x y)
+(ADDQ x (ADDQconst [c] y)) -> (LEAQ1 [c] x y)
+
 // fold ADDQ into LEAQ
 (ADDQconst [c] (LEAQ [d] {s} x)) -> (LEAQ [c+d] {s} x)
 (LEAQ [c] {s} (ADDQconst [d] x)) -> (LEAQ [c+d] {s} x)
@@ -818,7 +823,6 @@
 (LEAQ [off1] {sym1} (LEAQ8 [off2] {sym2} x y)) && canMergeSym(sym1, sym2) ->
       (LEAQ8 [addOff(off1,off2)] {mergeSym(sym1,sym2)} x y)
 
-
 // lower Zero instructions with word sizes
 (Zero [0] _ mem) -> mem
 (Zero [1] destptr mem) -> (MOVBstoreconst [0] destptr mem)

src/cmd/compile/internal/ssa/rewriteAMD64.go

@@ -1075,6 +1075,38 @@ func rewriteValueAMD64_OpAMD64ADDQ(v *Value, config *Config) bool {
 		v.AddArg(x)
 		return true
 	}
+	// match: (ADDQ (ADDQconst [c] x) y)
+	// cond:
+	// result: (LEAQ1 [c] x y)
+	for {
+		if v.Args[0].Op != OpAMD64ADDQconst {
+			break
+		}
+		c := v.Args[0].AuxInt
+		x := v.Args[0].Args[0]
+		y := v.Args[1]
+		v.reset(OpAMD64LEAQ1)
+		v.AuxInt = c
+		v.AddArg(x)
+		v.AddArg(y)
+		return true
+	}
+	// match: (ADDQ x (ADDQconst [c] y))
+	// cond:
+	// result: (LEAQ1 [c] x y)
+	for {
+		x := v.Args[0]
+		if v.Args[1].Op != OpAMD64ADDQconst {
+			break
+		}
+		c := v.Args[1].AuxInt
+		y := v.Args[1].Args[0]
+		v.reset(OpAMD64LEAQ1)
+		v.AuxInt = c
+		v.AddArg(x)
+		v.AddArg(y)
+		return true
+	}
 	// match: (ADDQ x (LEAQ [c] {s} y))
 	// cond: x.Op != OpSB && y.Op != OpSB
 	// result: (LEAQ1 [c] {s} x y)
@@ -1136,6 +1168,22 @@ func rewriteValueAMD64_OpAMD64ADDQ(v *Value, config *Config) bool {
 func rewriteValueAMD64_OpAMD64ADDQconst(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
+	// match: (ADDQconst [c] (ADDQ x y))
+	// cond:
+	// result: (LEAQ1 [c] x y)
+	for {
+		c := v.AuxInt
+		if v.Args[0].Op != OpAMD64ADDQ {
+			break
+		}
+		x := v.Args[0].Args[0]
+		y := v.Args[0].Args[1]
+		v.reset(OpAMD64LEAQ1)
+		v.AuxInt = c
+		v.AddArg(x)
+		v.AddArg(y)
+		return true
+	}
 	// match: (ADDQconst [c] (LEAQ [d] {s} x))
 	// cond:
 	// result: (LEAQ [c+d] {s} x)