From 5379f412bc6ac6171f3bd73930197bfce88c2faa Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Fri, 19 Dec 2008 20:58:01 +0000
Subject: Fix PR3149. If an early clobber def is a physical register and it is
 tied to an input operand, it effectively extends the live range of the
 physical register. Currently we do not have a good way to represent this.

172     %ECX<def> = MOV32rr %reg1039<kill>
180     INLINEASM <es:subl $5,$1
        sbbl $3,$0>, 10, %EAX<def>, 14, %ECX<earlyclobber,def>, 9, %EAX<kill>,
36, <fi#0>, 1, %reg0, 0, 9, %ECX<kill>, 36, <fi#1>, 1, %reg0, 0
188     %EAX<def> = MOV32rr %EAX<kill>
196     %ECX<def> = MOV32rr %ECX<kill>
204     %ECX<def> = MOV32rr %ECX<kill>
212     %EAX<def> = MOV32rr %EAX<kill>
220     %EAX<def> = MOV32rr %EAX
228     %reg1039<def> = MOV32rr %ECX<kill>

The early clobber operand ties ECX input to the ECX def.

The live interval of ECX is represented as this:
%reg20,inf = [46,47:1)[174,230:0)  0@174-(230) 1@46-(47)

The right way to represent this is something like
%reg20,inf = [46,47:2)[174,182:1)[181:230:0)  0@174-(182) 1@181-230 @2@46-(47)

Of course that won't work since that means overlapping live ranges defined by two val#.

The workaround for now is to add a bit to val# which says the val# is redefined by a early clobber def somewhere. This prevents the move at 228 from being optimized away by SimpleRegisterCoalescing::AdjustCopiesBackFrom.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61259 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SimpleRegisterCoalescing.cpp | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

(limited to 'lib/CodeGen/SimpleRegisterCoalescing.cpp')

diff --git a/lib/CodeGen/SimpleRegisterCoalescing.cpp b/lib/CodeGen/SimpleRegisterCoalescing.cpp
index 41022a6e26..cfac82613f 100644
--- a/lib/CodeGen/SimpleRegisterCoalescing.cpp
+++ b/lib/CodeGen/SimpleRegisterCoalescing.cpp
@@ -119,6 +119,26 @@ bool SimpleRegisterCoalescing::AdjustCopiesBackFrom(LiveInterval &IntA,
   if (ALR == IntA.end()) // Should never happen!
     return false;
   VNInfo *AValNo = ALR->valno;
+  // If it's re-defined by an early clobber somewhere in the live range, then
+  // it's not safe to eliminate the copy. FIXME: This is a temporary workaround.
+  // See PR3149:
+  // 172     %ECX<def> = MOV32rr %reg1039<kill>
+  // 180     INLINEASM <es:subl $5,$1
+  //         sbbl $3,$0>, 10, %EAX<def>, 14, %ECX<earlyclobber,def>, 9, %EAX<kill>,
+  // 36, <fi#0>, 1, %reg0, 0, 9, %ECX<kill>, 36, <fi#1>, 1, %reg0, 0
+  // 188     %EAX<def> = MOV32rr %EAX<kill>
+  // 196     %ECX<def> = MOV32rr %ECX<kill>
+  // 204     %ECX<def> = MOV32rr %ECX<kill>
+  // 212     %EAX<def> = MOV32rr %EAX<kill>
+  // 220     %EAX<def> = MOV32rr %EAX
+  // 228     %reg1039<def> = MOV32rr %ECX<kill>
+  // The early clobber operand ties ECX input to the ECX def.
+  //
+  // The live interval of ECX is represented as this:
+  // %reg20,inf = [46,47:1)[174,230:0)  0@174-(230) 1@46-(47)
+  // The coalescer has no idea there was a def in the middle of [174,230].
+  if (AValNo->redefByEC)
+    return false;
   
   // If AValNo is defined as a copy from IntB, we can potentially process this.  
   // Get the instruction that defines this value number.
-- 
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