[llvm] r216750 - [FastISel][AArch64] Fix an incorrect kill flag due to a bug in SelectTrunc.

[Juergen Ributzka]

Author: ributzka
Date: Fri Aug 29 12:58:16 2014
New Revision: 216750

URL: http://llvm.org/viewvc/llvm-project?rev=216750&view=rev
Log:
[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.

Added:
    llvm/trunk/test/CodeGen/AArch64/fast-isel-trunc.ll
Modified:
    llvm/trunk/lib/Target/AArch64/AArch64FastISel.cpp

Modified: llvm/trunk/lib/Target/AArch64/AArch64FastISel.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AArch64/AArch64FastISel.cpp?rev=216750&r1=216749&r2=216750&view=diff
==============================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64FastISel.cpp (original)
+++ llvm/trunk/lib/Target/AArch64/AArch64FastISel.cpp Fri Aug 29 12:58:16 2014
@@ -2694,8 +2694,11 @@ bool AArch64FastISel::SelectTrunc(const
   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
     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;
 }
 

Added: llvm/trunk/test/CodeGen/AArch64/fast-isel-trunc.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/fast-isel-trunc.ll?rev=216750&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/AArch64/fast-isel-trunc.ll (added)
+++ llvm/trunk/test/CodeGen/AArch64/fast-isel-trunc.ll Fri Aug 29 12:58:16 2014
@@ -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
+}