[llvm] bfc961a - [TargetLowering] Check boolean content when folding bit compare

[Sven van Haastregt via llvm-commits]

Author: Sven van Haastregt
Date: 2020-10-21T11:46:55+01:00
New Revision: bfc961aeb2d0e5a05bca7a894cbc4370f5e79a6a

URL: https://github.com/llvm/llvm-project/commit/bfc961aeb2d0e5a05bca7a894cbc4370f5e79a6a
DIFF: https://github.com/llvm/llvm-project/commit/bfc961aeb2d0e5a05bca7a894cbc4370f5e79a6a.diff

LOG: [TargetLowering] Check boolean content when folding bit compare

Updates an optimization that relies on boolean contents being either 0
or 1 to properly check for this before triggering.

The following:
  (X & 8) != 0 --> (X & 8) >> 3
Produces unexpected results when a boolean 'true' value is represented
by negative one.

Patch by Erik Hogeman.

Differential Revision: https://reviews.llvm.org/D89390

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
    llvm/test/CodeGen/NVPTX/pow2_mask_cmp.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 3e6c11a0c129..bc81d0d8298c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -3981,7 +3981,8 @@ SDValue TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
     EVT ShValTy = N0.getValueType();
 
     // Fold bit comparisons when we can.
-    if ((Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
+    if (getBooleanContents(N0.getValueType()) == ZeroOrOneBooleanContent &&
+        (Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
         (VT == ShValTy || (isTypeLegal(VT) && VT.bitsLE(ShValTy))) &&
         N0.getOpcode() == ISD::AND) {
       if (auto *AndRHS = dyn_cast<ConstantSDNode>(N0.getOperand(1))) {

diff  --git a/llvm/test/CodeGen/NVPTX/pow2_mask_cmp.ll b/llvm/test/CodeGen/NVPTX/pow2_mask_cmp.ll
index 13e35d940528..45701df28a30 100644
--- a/llvm/test/CodeGen/NVPTX/pow2_mask_cmp.ll
+++ b/llvm/test/CodeGen/NVPTX/pow2_mask_cmp.ll
@@ -3,8 +3,14 @@
 ; Tests the following pattern:
 ; (X & 8) != 0 --> (X & 8) >> 3
 
+; This produces incorrect code when boolean false is represented
+; as a negative one, and this test checks that the transform is
+; not triggered.
+
 ; CHECK-LABEL: @pow2_mask_cmp
-; CHECK: bfe.u32 {{%r[0-9]+}}, {{%r[0-9]+}}, 3, 1
+; CHECK: and.b32 [[AND:%r[0-9]+]], %r{{[0-9]+}}, 8
+; CHECK: setp.ne.s32 [[SETP:%p[0-9+]]], [[AND]], 0
+; CHECK: selp.u32 %r{{[0-9]+}}, 1, 0, [[SETP]]
 define i32 @pow2_mask_cmp(i32 %x) {
   %a = and i32 %x, 8
   %cmp = icmp ne i32 %a, 0