Fix for PR3225: disable a broken optimization in

DAGTypeLegalizer::ExpandShiftWithKnownAmountBit.

In terms of restoring the optimization, the best fix here isn't
obvious... any ideas?

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61119 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp b/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
index 8e86405..8abf144 100644 (file)
--- a/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
@@ -1211,6 +1211,8 @@ ExpandShiftWithKnownAmountBit(SDNode *N, SDValue &Lo, SDValue &Hi) {
     }
   }
 
+#if 0
+  // FIXME: This code is broken for shifts with a zero amount!
   // If we know that all of the high bits of the shift amount are zero, then we
   // can do this as a couple of simple shifts.
   if ((KnownZero & HighBitMask) == HighBitMask) {
@@ -1232,6 +1234,7 @@ ExpandShiftWithKnownAmountBit(SDNode *N, SDValue &Lo, SDValue &Hi) {
                      DAG.getNode(Op2, NVT, InL, Amt2));
     return true;
   }
+#endif
 
   return false;
 }

diff --git a/test/CodeGen/X86/2008-12-16-BadShift.ll b/test/CodeGen/X86/2008-12-16-BadShift.ll
new file mode 100644 (file)
index 0000000..46b7018
--- /dev/null
+++ b/test/CodeGen/X86/2008-12-16-BadShift.ll
@@ -0,0 +1,19 @@
+; RUN: llvm-as < %s | llc | not grep shrl
+; Note: this test is really trying to make sure that the shift
+; returns the right result; shrl is most likely wrong,
+; but if CodeGen starts legitimately using an shrl here,
+; please adjust the test appropriately.
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"
+target triple = "i386-pc-linux-gnu"
+@.str = internal constant [6 x i8] c"%lld\0A\00"               ; <[6 x i8]*> [#uses=1]
+
+define i64 @mebbe_shift(i32 %xx, i32 %test) nounwind {
+entry:
+       %conv = zext i32 %xx to i64             ; <i64> [#uses=1]
+       %tobool = icmp ne i32 %test, 0          ; <i1> [#uses=1]
+       %shl = select i1 %tobool, i64 3, i64 0          ; <i64> [#uses=1]
+       %x.0 = shl i64 %conv, %shl              ; <i64> [#uses=1]
+       ret i64 %x.0
+}
+