From f9f04c25b22dadbbbd1f56d72c152ff341ee8c28 Mon Sep 17 00:00:00 2001
From: Pete Cooper <peter_cooper@apple.com>
Date: Fri, 8 May 2015 20:46:54 +0000
Subject: [PATCH] [Fast-ISel] Clear kill flags on registers replaced by
 updateValueMap.

When selecting an extract instruction, we don't actually generate code but instead work out which register we are reading, and rewrite uses of the extract def to the source register.  This is done via updateValueMap,.

However, its possible that the source register we are rewriting *to* to also have uses.  If those uses are after a kill of the value we are rewriting *from* then we have uses after a kill and the verifier fails.

This code checks for the case where the to register is also used, and if so it clears all kill on the from register.  This is conservative, but better that always clearing kills on the from register.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236897 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp |  7 ++++++
 .../fast-isel-update-valuemap-for-extract.ll  | 24 +++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 test/CodeGen/ARM/fast-isel-update-valuemap-for-extract.ll

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index e208076a62e..175434e94f8 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -578,6 +578,13 @@ bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
         TargetRegisterInfo::isVirtualRegister(To))
       MRI.constrainRegClass(To, MRI.getRegClass(From));
     // Replace it.
+
+
+    // Replacing one register with another won't touch the kill flags.
+    // We need to conservatively clear the kill flags as a kill on the old
+    // register might dominate existing uses of the new register.
+    if (!MRI.use_empty(To))
+      MRI.clearKillFlags(From);
     MRI.replaceRegWith(From, To);
   }
 
diff --git a/test/CodeGen/ARM/fast-isel-update-valuemap-for-extract.ll b/test/CodeGen/ARM/fast-isel-update-valuemap-for-extract.ll
new file mode 100644
index 00000000000..18d60fee189
--- /dev/null
+++ b/test/CodeGen/ARM/fast-isel-update-valuemap-for-extract.ll
@@ -0,0 +1,24 @@
+; RUN: llc %s -o - -fast-isel=true -O0 -verify-machineinstrs | FileCheck %s
+
+target datalayout = "e-m:o-p:32:32-f64:32:64-v64:32:64-v128:32:128-a:0:32-n32-S32"
+target triple = "thumbv7-apple-ios8.0.0"
+
+; This test ensures that when fast-isel rewrites uses of the vreg for %tmp29, it also
+; updates kill flags on the shift instruction generated as part of the gep.
+; This was failing instruction verification.
+
+; CHECK-LABEL: @test
+
+%struct.node = type opaque
+
+declare void @foo([4 x i32], %struct.node*)
+
+define void @test([4 x i32] %xpic.coerce, %struct.node* %t) {
+bb:
+  %tmp29 = extractvalue [4 x i32] %xpic.coerce, 0
+  %tmp40 = bitcast %struct.node* %t to [8 x %struct.node*]*
+  %tmp41 = getelementptr inbounds [8 x %struct.node*], [8 x %struct.node*]* %tmp40, i32 0, i32 %tmp29
+  %tmp42 = load %struct.node*, %struct.node** %tmp41, align 4
+  call void @foo([4 x i32] %xpic.coerce, %struct.node* %tmp42)
+  ret void
+}
-- 
2.34.1