[DAGCombiner] PCMP* sets its result to all ones or zeros so we can AND with the

shifted mask rather than masking and shifting separately.

The patch adds this transformation to the DAGCombiner:

  (shl (and (setcc:i8v16 ...) N01C) N1C) -> (and (setcc:i8v16 ...) N01C<<N1C)

<rdar://problem/16054492>

Patch by Adam Nemet <anemet@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201906 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index de8fbc9d789367d56e2c9dfb1a7197a314401d16..76974c26d99779b0569896478b979994e8bc5b4f 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3818,6 +3818,24 @@ SDValue DAGCombiner::visitSHL(SDNode *N) {
   if (VT.isVector()) {
     SDValue FoldedVOp = SimplifyVBinOp(N);
     if (FoldedVOp.getNode()) return FoldedVOp;
+
+    BuildVectorSDNode *N1CV = dyn_cast<BuildVectorSDNode>(N1);
+    // If setcc produces all-one true value then:
+    // (shl (and (setcc) N01CV) N1CV) -> (and (setcc) N01CV<<N1CV)
+    if (N1CV && N1CV->isConstant() &&
+        TLI.getBooleanContents(true) ==
+          TargetLowering::ZeroOrNegativeOneBooleanContent &&
+        N0.getOpcode() == ISD::AND) {
+      SDValue N00 = N0->getOperand(0);
+      SDValue N01 = N0->getOperand(1);
+      BuildVectorSDNode *N01CV = dyn_cast<BuildVectorSDNode>(N01);
+
+      if (N01CV && N01CV->isConstant() && N00.getOpcode() == ISD::SETCC) {
+        SDValue C = DAG.FoldConstantArithmetic(ISD::SHL, VT, N01CV, N1CV);
+        if (C.getNode())
+          return DAG.getNode(ISD::AND, SDLoc(N), VT, N00, C);
+      }
+    }
   }
 
   // fold (shl c1, c2) -> c1<<c2

diff --git a/test/CodeGen/X86/shift-pcmp.ll b/test/CodeGen/X86/shift-pcmp.ll
new file mode 100644 (file)
index 0000000..b15fb10
--- /dev/null
+++ b/test/CodeGen/X86/shift-pcmp.ll
@@ -0,0 +1,30 @@
+; RUN: llc < %s -o - -mcpu=generic -march=x86-64 -mattr=+sse2 | FileCheck %s
+; RUN: llc < %s -o - -mcpu=generic -march=x86-64 -mattr=+avx | FileCheck %s
+
+define <8 x i16> @foo(<8 x i16> %a, <8 x i16> %b) {
+; CHECK: .short              32
+; CHECK-NEXT: .short         32
+; CHECK-NEXT: .short         32
+; CHECK-NEXT: .short         32
+; CHECK-NEXT: .short         32
+; CHECK-NEXT: .short         32
+; CHECK-NEXT: .short         32
+; CHECK-NEXT: .short         32
+; CHECK-LABEL: foo
+; CHECK-NOT: psll
+entry:
+  %icmp = icmp eq <8 x i16> %a, %b
+  %zext = zext <8 x i1> %icmp to <8 x i16>
+  %shl = shl nuw nsw <8 x i16> %zext, <i16 5, i16 5, i16 5, i16 5, i16 5, i16 5, i16 5, i16 5>
+  ret <8 x i16> %shl
+}
+
+; Don't fail with an assert due to an undef in the buildvector
+define <8 x i16> @bar(<8 x i16> %a, <8 x i16> %b) {
+; CHECK-LABEL: bar
+entry:
+  %icmp = icmp eq <8 x i16> %a, %b
+  %zext = zext <8 x i1> %icmp to <8 x i16>
+  %shl = shl nuw nsw <8 x i16> %zext, <i16 5, i16 undef, i16 5, i16 5, i16 5, i16 5, i16 5, i16 5>
+  ret <8 x i16> %shl
+}