From d8835d09ecbb10919e5c8355aa1beb311d6d2ca7 Mon Sep 17 00:00:00 2001
From: Juergen Ributzka <juergen@apple.com>
Date: Fri, 29 Aug 2014 17:58:16 +0000
Subject: [PATCH] [FastISel][AArch64] Fix an incorrect kill flag due to a bug
 in SelectTrunc.

When we select a trunc instruction we don't emit any code if the type is already
i32 or smaller. This is because the instruction that uses the truncated value
will deal with it.

This behavior can incorrectly transfer a kill flag, which was meant for the
result of the truncate, onto the source register.

%2 = trunc i32 %1 to i16
... = ... %2                -> ... = ... vreg1 <kill>
... = ... %1                   ... = ... vreg1

This commit fixes this by emitting a COPY instruction, so that the result and
source register are distinct virtual registers.

This fixes rdar://problem/18178188.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216750 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/AArch64/AArch64FastISel.cpp  | 19 +++++++++++++------
 test/CodeGen/AArch64/fast-isel-trunc.ll | 12 ++++++++++++
 2 files changed, 25 insertions(+), 6 deletions(-)
 create mode 100644 test/CodeGen/AArch64/fast-isel-trunc.ll

diff --git a/lib/Target/AArch64/AArch64FastISel.cpp b/lib/Target/AArch64/AArch64FastISel.cpp
index 179fe4dd7ff..7ee8c47930a 100644
--- a/lib/Target/AArch64/AArch64FastISel.cpp
+++ b/lib/Target/AArch64/AArch64FastISel.cpp
@@ -2694,8 +2694,11 @@ bool AArch64FastISel::SelectTrunc(const Instruction *I) {
   bool SrcIsKill = hasTrivialKill(Op);
 
   // If we're truncating from i64 to a smaller non-legal type then generate an
-  // AND.  Otherwise, we know the high bits are undefined and a truncate doesn't
-  // generate any code.
+  // AND. Otherwise, we know the high bits are undefined and a truncate only
+  // generate a COPY. We cannot mark the source register also as result
+  // register, because this can incorrectly transfer the kill flag onto the
+  // source register.
+  unsigned ResultReg;
   if (SrcVT == MVT::i64) {
     uint64_t Mask = 0;
     switch (DestVT.SimpleTy) {
@@ -2716,12 +2719,16 @@ bool AArch64FastISel::SelectTrunc(const Instruction *I) {
     unsigned Reg32 = FastEmitInst_extractsubreg(MVT::i32, SrcReg, SrcIsKill,
                                                 AArch64::sub_32);
     // Create the AND instruction which performs the actual truncation.
-    unsigned ANDReg = emitAND_ri(MVT::i32, Reg32, /*IsKill=*/true, Mask);
-    assert(ANDReg && "Unexpected AND instruction emission failure.");
-    SrcReg = ANDReg;
+    ResultReg = emitAND_ri(MVT::i32, Reg32, /*IsKill=*/true, Mask);
+    assert(ResultReg && "Unexpected AND instruction emission failure.");
+  } else {
+    ResultReg = createResultReg(&AArch64::GPR32RegClass);
+    BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc,
+            TII.get(TargetOpcode::COPY), ResultReg)
+        .addReg(SrcReg, getKillRegState(SrcIsKill));
   }
 
-  UpdateValueMap(I, SrcReg);
+  UpdateValueMap(I, ResultReg);
   return true;
 }
 
diff --git a/test/CodeGen/AArch64/fast-isel-trunc.ll b/test/CodeGen/AArch64/fast-isel-trunc.ll
new file mode 100644
index 00000000000..55937eb76fa
--- /dev/null
+++ b/test/CodeGen/AArch64/fast-isel-trunc.ll
@@ -0,0 +1,12 @@
+; RUN: llc -mtriple=aarch64-apple-darwin -fast-isel -fast-isel-abort -verify-machineinstrs < %s
+
+; Test that %1 doesn't get the kill flag set before its last use.
+define i32 @test_trunc(i32 %a) {
+  %1 = add i32 %a, 1
+  %2 = trunc i32 %1 to i16
+  %3 = icmp ult i16 1, %2
+  %4 = add i32 %1, 1
+  %5 = sext i1 %3 to i32
+  %6 = and i32 %4, %5
+  ret i32 %6
+}
-- 
2.34.1