From 3294014ae119f34c40547ed253bf4c5d25dc5f17 Mon Sep 17 00:00:00 2001
From: Josh Bleecher Snyder <josharian@gmail.com>
Date: Fri, 4 Mar 2016 14:12:44 -0800
Subject: [PATCH] cmd/compile: collapse OffPtr sequences

This triggers an astonishing 160k times
during make.bash. The second biggest
generic rewrite triggers 100k times.

However, this is really just moving
rewrites that were happening at the
architecture level to the generic level.

Change-Id: Ife06fe5234f31433328460cb2e0741c071deda41
Reviewed-on: https://go-review.googlesource.com/20235
Run-TryBot: Todd Neal <todd@tneal.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Todd Neal <todd@tneal.org>
---
 .../compile/internal/ssa/gen/generic.rules    |  3 +++
 .../compile/internal/ssa/rewritegeneric.go    | 22 +++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/src/cmd/compile/internal/ssa/gen/generic.rules b/src/cmd/compile/internal/ssa/gen/generic.rules
index 0c77a6dee8..994e880bc6 100644
--- a/src/cmd/compile/internal/ssa/gen/generic.rules
+++ b/src/cmd/compile/internal/ssa/gen/generic.rules
@@ -404,6 +404,9 @@
 // Load of store of same address, with compatibly typed value and same size
 (Load <t1> p1 (Store [w] p2 x _)) && isSamePtr(p1,p2) && t1.Compare(x.Type)==CMPeq && w == t1.Size() -> x
 
+// Collapse OffPtr
+(OffPtr (OffPtr p [b]) [a]) -> (OffPtr p [a+b])
+
 
 // indexing operations
 // Note: bounds check has already been done
diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index 1ed5fa9555..79dcf9a716 100644
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -206,6 +206,8 @@ func rewriteValuegeneric(v *Value, config *Config) bool {
 		return rewriteValuegeneric_OpNeqPtr(v, config)
 	case OpNeqSlice:
 		return rewriteValuegeneric_OpNeqSlice(v, config)
+	case OpOffPtr:
+		return rewriteValuegeneric_OpOffPtr(v, config)
 	case OpOr16:
 		return rewriteValuegeneric_OpOr16(v, config)
 	case OpOr32:
@@ -4821,6 +4823,26 @@ func rewriteValuegeneric_OpNeqSlice(v *Value, config *Config) bool {
 	}
 	return false
 }
+func rewriteValuegeneric_OpOffPtr(v *Value, config *Config) bool {
+	b := v.Block
+	_ = b
+	// match: (OffPtr (OffPtr p [b]) [a])
+	// cond:
+	// result: (OffPtr p [a+b])
+	for {
+		if v.Args[0].Op != OpOffPtr {
+			break
+		}
+		p := v.Args[0].Args[0]
+		b := v.Args[0].AuxInt
+		a := v.AuxInt
+		v.reset(OpOffPtr)
+		v.AddArg(p)
+		v.AuxInt = a + b
+		return true
+	}
+	return false
+}
 func rewriteValuegeneric_OpOr16(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b