From a7a199947a15d48d405be809278a7ea7c6ebf03a Mon Sep 17 00:00:00 2001
From: =?utf8?q?Alexandru=20Mo=C8=99oi?= <mosoi@google.com>
Date: Fri, 18 Mar 2016 10:50:00 +0100
Subject: [PATCH] cmd/compile: add rules to simplify AddPtr
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Fixes #14849

Change-Id: I86e2dc27ca73bb6b24261a68cbf0094a63167414
Reviewed-on: https://go-review.googlesource.com/20833
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>
---
 .../compile/internal/ssa/gen/generic.rules    |  3 ++
 .../compile/internal/ssa/rewritegeneric.go    | 39 +++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/src/cmd/compile/internal/ssa/gen/generic.rules b/src/cmd/compile/internal/ssa/gen/generic.rules
index cbb8fc625c..8458619bf2 100644
--- a/src/cmd/compile/internal/ssa/gen/generic.rules
+++ b/src/cmd/compile/internal/ssa/gen/generic.rules
@@ -48,6 +48,7 @@
 (Add32F (Const32F [c]) (Const32F [d])) -> 
         (Const32F [f2i(float64(i2f32(c) + i2f32(d)))]) // ensure we combine the operands with 32 bit precision
 (Add64F (Const64F [c]) (Const64F [d])) -> (Const64F [f2i(i2f(c) + i2f(d))])
+(AddPtr <t> x (Const64 [c])) -> (OffPtr <t> x [c])
 
 (Sub8 (Const8 [c]) (Const8 [d])) -> (Const8 [c-d])
 (Sub16 (Const16 [c]) (Const16 [d])) -> (Const16 [c-d])
@@ -156,6 +157,7 @@
 (Neq8 x (Const8 <t> [c])) && x.Op != OpConst8 -> (Neq8 (Const8 <t> [c]) x)
 (Neq8 x (ConstBool <t> [c])) && x.Op != OpConstBool -> (Neq8 (ConstBool <t> [c]) x)
 
+// AddPtr is not canonicalized because nilcheck ptr checks the first argument to be non-nil.
 (Add64 x (Const64 <t> [c])) && x.Op != OpConst64 -> (Add64 (Const64 <t> [c]) x)
 (Add32 x (Const32 <t> [c])) && x.Op != OpConst32 -> (Add32 (Const32 <t> [c]) x)
 (Add16 x (Const16 <t> [c])) && x.Op != OpConst16 -> (Add16 (Const16 <t> [c]) x)
@@ -443,6 +445,7 @@
 
 // Collapse OffPtr
 (OffPtr (OffPtr p [b]) [a]) -> (OffPtr p [a+b])
+(OffPtr p [0]) && v.Type.Compare(p.Type) == CMPeq -> p
 
 
 // indexing operations
diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index bf08dd102b..9b304d8acf 100644
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -20,6 +20,8 @@ func rewriteValuegeneric(v *Value, config *Config) bool {
 		return rewriteValuegeneric_OpAdd64F(v, config)
 	case OpAdd8:
 		return rewriteValuegeneric_OpAdd8(v, config)
+	case OpAddPtr:
+		return rewriteValuegeneric_OpAddPtr(v, config)
 	case OpAnd16:
 		return rewriteValuegeneric_OpAnd16(v, config)
 	case OpAnd32:
@@ -617,6 +619,27 @@ func rewriteValuegeneric_OpAdd8(v *Value, config *Config) bool {
 	}
 	return false
 }
+func rewriteValuegeneric_OpAddPtr(v *Value, config *Config) bool {
+	b := v.Block
+	_ = b
+	// match: (AddPtr <t> x (Const64 [c]))
+	// cond:
+	// result: (OffPtr <t> x [c])
+	for {
+		t := v.Type
+		x := v.Args[0]
+		if v.Args[1].Op != OpConst64 {
+			break
+		}
+		c := v.Args[1].AuxInt
+		v.reset(OpOffPtr)
+		v.Type = t
+		v.AddArg(x)
+		v.AuxInt = c
+		return true
+	}
+	return false
+}
 func rewriteValuegeneric_OpAnd16(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
@@ -5242,6 +5265,22 @@ func rewriteValuegeneric_OpOffPtr(v *Value, config *Config) bool {
 		v.AuxInt = a + b
 		return true
 	}
+	// match: (OffPtr p [0])
+	// cond: v.Type.Compare(p.Type) == CMPeq
+	// result: p
+	for {
+		p := v.Args[0]
+		if v.AuxInt != 0 {
+			break
+		}
+		if !(v.Type.Compare(p.Type) == CMPeq) {
+			break
+		}
+		v.reset(OpCopy)
+		v.Type = p.Type
+		v.AddArg(p)
+		return true
+	}
 	return false
 }
 func rewriteValuegeneric_OpOr16(v *Value, config *Config) bool {
-- 
2.48.1