[AMDGPU] Combine and (srl) into shl (bfe)

Perform DAG combine:
and (srl x, c), mask => shl (bfe x, nb + c, mask >> nb), nb
Where nb is a number of trailing zeroes in mask.

It replaces two instructions with two and BFE is generally a more
expensive one. However this is only done if we are selecting a byte
or word at an aligned boundary which results in a proper SDWA
operand pattern. It is only done if SDWA is supported.

TODO: improve SDWA pass to actually convert this pattern. It is not
done now because we have an immediate in the instruction, which has
be moved into a VGPR.

Differential Revision: https://reviews.llvm.org/D33455

llvm-svn: 303681

1 files changed, 4 insertions, 4 deletions

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h b/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h
index d122af0e27b..24ebde5dc93 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h
@@ -420,6 +420,10 @@ public:
     return getGeneration() < AMDGPUSubtarget::VOLCANIC_ISLANDS;
   }
 
+  bool hasSDWA() const {
+    return HasSDWA;
+  }
+
   /// \brief Returns the offset in bytes from the start of the input buffer
   ///        of the first explicit kernel argument.
   unsigned getExplicitKernelArgOffset(const MachineFunction &MF) const {
@@ -674,10 +678,6 @@ public:
     return HasInv2PiInlineImm;
   }
 
-  bool hasSDWA() const {
-    return HasSDWA;
-  }
-
   bool hasDPP() const {
     return HasDPP;
   }