From f69bb5e43c1427d23800e4e678a7c2f2088f0c88 Mon Sep 17 00:00:00 2001
From: Lang Hames <lhames@gmail.com>
Date: Mon, 21 Apr 2014 08:18:53 +0000
Subject: [X86] ISEL (and X, <constant mask>) to BZHI when BMI2 is available.

Generating BZHI in the variable mask case, i.e. (and X, (sub (shl 1, N), 1)),
was already supported, but we were missing the constant-mask case. This patch
fixes that.

<rdar://problem/15480077>



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206738 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/X86/X86ISelLowering.cpp | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

(limited to 'lib')

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 306fb7e199..d867414a98 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -18503,6 +18503,20 @@ static SDValue PerformAndCombine(SDNode *N, SelectionDAG &DAG,
       }
     } // BEXTR
 
+    // Check for BZHI with contiguous mask: (and X, 0x0..0f..f)
+    // This should be checked after BEXTR - when X is a shift, a BEXTR is
+    // preferrable.
+    if (Subtarget->hasBMI2()) {
+      if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(N1)) {
+        uint64_t Mask = C->getZExtValue();
+        if (isMask_64(Mask)) {
+          unsigned LZ = CountTrailingOnes_64(Mask);
+          return DAG.getNode(X86ISD::BZHI, DL, VT, N0,
+                             DAG.getConstant(LZ, MVT::i8));
+        }
+      }
+    }
+
     return SDValue();
   }
 
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