From 9e23336d0c99fc5cae04037ead6d8f2b677e8764 Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Wed, 12 Mar 2008 22:19:41 +0000
Subject: Experimental scheduler change to schedule / coalesce the copies added
 for function livein's. Take 2008-03-10-RegAllocInfLoop.ll, the schedule looks
 like this after these copies are inserted:

entry: 0x12049d0, LLVM BB @0x1201fd0, ID#0:
Live Ins: %EAX %EDX %ECX
        %reg1031<def> = MOVPC32r 0
        %reg1032<def> = ADD32ri %reg1031, <es:_GLOBAL_OFFSET_TABLE_>, %EFLAGS<imp-def>
        %reg1028<def> = MOV32rr %EAX
        %reg1029<def> = MOV32rr %EDX
        %reg1030<def> = MOV32rr %ECX
        %reg1027<def> = MOV8rm %reg0, 1, %reg0, 0, Mem:LD(1,1) [0x1201910 + 0]
        %reg1025<def> = MOV32rr %reg1029
        %reg1026<def> = MOV32rr %reg1030
        %reg1024<def> = MOV32rr %reg1028

The copies unnecessarily increase register pressure and it will end up requiring a physical register to be spilled.

With -schedule-livein-copies:
entry: 0x12049d0, LLVM BB @0x1201fa0, ID#0:
Live Ins: %EAX %EDX %ECX
        %reg1031<def> = MOVPC32r 0
        %reg1032<def> = ADD32ri %reg1031, <es:_GLOBAL_OFFSET_TABLE_>, %EFLAGS<imp-def>
        %reg1024<def> = MOV32rr %EAX
        %reg1025<def> = MOV32rr %EDX
        %reg1026<def> = MOV32rr %ECX
        %reg1027<def> = MOV8rm %reg0, 1, %reg0, 0, Mem:LD(1,1) [0x12018e0 + 0]

Much better!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48307 91177308-0d34-0410-b5e6-96231b3b80d8
---
 test/CodeGen/X86/2008-03-10-RegAllocInfLoop.ll | 1 +
 1 file changed, 1 insertion(+)

(limited to 'test')

diff --git a/test/CodeGen/X86/2008-03-10-RegAllocInfLoop.ll b/test/CodeGen/X86/2008-03-10-RegAllocInfLoop.ll
index b858592..1098988 100644
--- a/test/CodeGen/X86/2008-03-10-RegAllocInfLoop.ll
+++ b/test/CodeGen/X86/2008-03-10-RegAllocInfLoop.ll
@@ -1,4 +1,5 @@
 ; RUN: llvm-as < %s | llc -mtriple=i386-pc-linux-gnu -relocation-model=pic -disable-fp-elim
+; RUN: llvm-as < %s | llc -mtriple=i386-pc-linux-gnu -relocation-model=pic -disable-fp-elim -schedule-livein-copies | not grep {Number of register spills}
 ; PR2134
 
 declare fastcc i8* @w_addchar(i8*, i32*, i32*, i8 signext ) nounwind 
-- 
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