[llvm] r319892 - [SystemZ] Bugfix in expandRxSBG()

[Jonas Paulsson via llvm-commits]

Author: jonpa
Date: Wed Dec  6 05:53:24 2017
New Revision: 319892

URL: http://llvm.org/viewvc/llvm-project?rev=319892&view=rev
Log:
[SystemZ]  Bugfix in expandRxSBG()

Csmith discovered a program that caused wrong code generation with -O0:

When handling a SIGN_EXTEND in expandRxSBG(), RxSBG.BitSize may be less than
the Input width (if a truncate was previously traversed), so maskMatters()
should be called with a masked based on the width of the sign extend result
instead.

Review: Ulrich Weigand

Added:
    llvm/trunk/test/CodeGen/SystemZ/rosbg-02.ll
Modified:
    llvm/trunk/lib/Target/SystemZ/SystemZISelDAGToDAG.cpp

Modified: llvm/trunk/lib/Target/SystemZ/SystemZISelDAGToDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/SystemZ/SystemZISelDAGToDAG.cpp?rev=319892&r1=319891&r2=319892&view=diff
==============================================================================
--- llvm/trunk/lib/Target/SystemZ/SystemZISelDAGToDAG.cpp (original)
+++ llvm/trunk/lib/Target/SystemZ/SystemZISelDAGToDAG.cpp Wed Dec  6 05:53:24 2017
@@ -838,9 +838,16 @@ bool SystemZDAGToDAGISel::expandRxSBG(Rx
   case ISD::SIGN_EXTEND: {
     // Check that the extension bits are don't-care (i.e. are masked out
     // by the final mask).
+    unsigned BitSize = N.getValueSizeInBits();
     unsigned InnerBitSize = N.getOperand(0).getValueSizeInBits();
-    if (maskMatters(RxSBG, allOnes(RxSBG.BitSize) - allOnes(InnerBitSize)))
-      return false;
+    if (maskMatters(RxSBG, allOnes(BitSize) - allOnes(InnerBitSize))) {
+      // In the case where only the sign bit is active, increase Rotate with
+      // the extension width.
+      if (RxSBG.Mask == 1 && RxSBG.Rotate == 1)
+        RxSBG.Rotate += (BitSize - InnerBitSize);
+      else
+        return false;
+    }
 
     RxSBG.Input = N.getOperand(0);
     return true;

Added: llvm/trunk/test/CodeGen/SystemZ/rosbg-02.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/SystemZ/rosbg-02.ll?rev=319892&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/SystemZ/rosbg-02.ll (added)
+++ llvm/trunk/test/CodeGen/SystemZ/rosbg-02.ll Wed Dec  6 05:53:24 2017
@@ -0,0 +1,24 @@
+; Test that a rosbg conversion involving a sign extend operation rotates with
+; the right number of steps.
+;
+; RUN: llc < %s -mtriple=s390x-linux-gnu -O0 | FileCheck %s
+
+ at g_136 = external global i16, align 2
+ at g_999 = external global i32, align 4
+
+; Function Attrs: nounwind
+define void @main() {
+  %1 = load i32, i32* undef, align 4
+  store i16 -28141, i16* @g_136, align 2
+  %2 = load i32, i32* undef, align 4
+  %3 = xor i32 -28141, %2
+  %4 = xor i32 %1, %3
+  %5 = sext i32 %4 to i64
+  %6 = icmp sgt i64 0, %5
+  %7 = zext i1 %6 to i32
+  %8 = load i32, i32* @g_999, align 4
+  %9 = or i32 %8, %7
+; CHECK: rosbg   %r1, %r3, 63, 63, 33
+  store i32 %9, i32* @g_999, align 4
+  ret void
+}