[AMDGPU] Check if type transforms to i16 (VI+) when getting AMDGPUISD::FFBH_U32

This will prevent following regression when enabling i16 support (D18049):

test/CodeGen/AMDGPU/ctlz.ll
test/CodeGen/AMDGPU/ctlz_zero_undef.ll

Differential Revision: https://reviews.llvm.org/D25802

llvm-svn: 285716

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.h b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.h
index cddef58d14e..07d2db82e32 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.h
@@ -25,6 +25,13 @@ class AMDGPUSubtarget;
 class MachineRegisterInfo;
 
 class AMDGPUTargetLowering : public TargetLowering {
+private:
+  /// \returns AMDGPUISD::FFBH_U32 node if the incoming \p Op may have been
+  /// legalized from a smaller type VT. Need to match pre-legalized type because
+  /// the generic legalization inserts the add/sub between the select and
+  /// compare.
+  SDValue getFFBH_U32(SelectionDAG &DAG, SDValue Op, const SDLoc &DL) const;
+
 protected:
   const AMDGPUSubtarget *Subtarget;