[PATCH] [X86] Replace (v)palignr intrinsics with generic shuffles (LLVM)

[Simon Pilgrim]

Hi craig.topper, andreadb, spatel, chandlerc,

The (v)palignr instructions are currently described using builtin intrinsics although the x86 shuffle lowering code now correctly identifies them.

This patch auto upgrades the palignr builtins to generic shuffles. I was also able to enable an old broken test (palign-2.ll).

Companion patch to D8301

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D8302

Files:
  lib/IR/AutoUpgrade.cpp
  test/CodeGen/X86/palignr-2.ll

Index: lib/IR/AutoUpgrade.cpp
===================================================================
--- lib/IR/AutoUpgrade.cpp
+++ lib/IR/AutoUpgrade.cpp
@@ -179,6 +179,8 @@
         Name == "x86.sse2.psrl.dq.bs" ||
         Name == "x86.avx2.psll.dq.bs" ||
         Name == "x86.avx2.psrl.dq.bs" ||
+        Name == "x86.ssse3.palign.r.128" ||
+        Name == "x86.avx2.palign.r.256" ||
         Name == "x86.sse41.pblendw" ||
         Name == "x86.sse41.blendpd" ||
         Name == "x86.sse41.blendps" ||
@@ -611,6 +613,50 @@
       unsigned Shift = cast<ConstantInt>(CI->getArgOperand(1))->getZExtValue();
       Rep = UpgradeX86PSRLDQIntrinsics(Builder, C, CI->getArgOperand(0), 2,
                                        Shift);
+    } else if (Name == "llvm.x86.ssse3.palign.r.128" ||
+               Name == "llvm.x86.avx2.palign.r.256") {
+      Value *Op0 = CI->getArgOperand(0);
+      Value *Op1 = CI->getArgOperand(1);
+      unsigned ShiftVal = cast<ConstantInt>(CI->getArgOperand(2))->getZExtValue();
+
+      VectorType *VecTy = cast<VectorType>(CI->getType());
+      unsigned VecBitWidth = VecTy->getBitWidth();
+      unsigned NumLanes = VecBitWidth / 128;
+      unsigned NumElts = NumLanes * 16;
+      unsigned NumLaneElts = NumElts / NumLanes;
+      assert(0 == (VecBitWidth % 128) && "Illegal vector width");
+      VectorType *ShufTy = VectorType::get(Type::getInt8Ty(C), NumElts);
+
+      // If palignr is shifting the pair of vectors more than the size of two
+      // lanes, emit zero.
+      if (ShiftVal >= (2 * NumLaneElts)) {
+        Rep = llvm::Constant::getNullValue(CI->getType());
+      } else {
+        // If palignr is shifting the pair of input vectors more than one lane,
+        // but less than two lanes, convert to shifting in zeroes.
+        if (ShiftVal > NumLaneElts) {
+          ShiftVal -= NumLaneElts;
+          Op0 = llvm::Constant::getNullValue(VecTy);
+        }
+
+        Op0 = Builder.CreateBitCast(Op0, ShufTy);
+        Op1 = Builder.CreateBitCast(Op1, ShufTy);
+
+        SmallVector<llvm::Constant*, 32> Indices;
+        // 256-bit palignr operates on 128-bit lanes so we need to handle that
+        for (unsigned l = 0; l != NumElts; l += NumLaneElts) {
+          for (unsigned i = 0; i != NumLaneElts; ++i) {
+            unsigned Idx = ShiftVal + i;
+            if (Idx >= NumLaneElts)
+              Idx += NumElts - NumLaneElts; // End of lane, switch operand.
+            Indices.push_back(llvm::ConstantInt::get(Type::getInt32Ty(C), Idx + l));
+          }
+        }
+
+        Value* SV = llvm::ConstantVector::get(Indices);
+        Rep = Builder.CreateShuffleVector(Op1, Op0, SV);
+        Rep = Builder.CreateBitCast(Rep, VecTy);
+      }
     } else if (Name == "llvm.x86.sse41.pblendw" ||
                Name == "llvm.x86.sse41.blendpd" ||
                Name == "llvm.x86.sse41.blendps" ||
Index: test/CodeGen/X86/palignr-2.ll
===================================================================
--- test/CodeGen/X86/palignr-2.ll
+++ test/CodeGen/X86/palignr-2.ll
@@ -8,8 +8,8 @@
 define void @t1(<2 x i64> %a, <2 x i64> %b) nounwind ssp {
 entry:
 ; CHECK-LABEL: t1:
-; palignr $3, %xmm1, %xmm0
-  %0 = tail call <2 x i64> @llvm.x86.ssse3.palign.r.128(<2 x i64> %a, <2 x i64> %b, i8 24) nounwind readnone
+; CHECK: palignr $3, %xmm1, %xmm0
+  %0 = tail call <2 x i64> @llvm.x86.ssse3.palign.r.128(<2 x i64> %a, <2 x i64> %b, i8 3) nounwind readnone
   store <2 x i64> %0, <2 x i64>* bitcast ([4 x i32]* @c to <2 x i64>*), align 16
   ret void
 }
@@ -19,10 +19,10 @@
 define void @t2() nounwind ssp {
 entry:
 ; CHECK-LABEL: t2:
-; palignr $4, _b, %xmm0
+; CHECK: palignr $4, _b, %xmm0
   %0 = load <2 x i64>, <2 x i64>* bitcast ([4 x i32]* @b to <2 x i64>*), align 16 ; <<2 x i64>> [#uses=1]
   %1 = load <2 x i64>, <2 x i64>* bitcast ([4 x i32]* @a to <2 x i64>*), align 16 ; <<2 x i64>> [#uses=1]
-  %2 = tail call <2 x i64> @llvm.x86.ssse3.palign.r.128(<2 x i64> %1, <2 x i64> %0, i8 32) nounwind readnone
+  %2 = tail call <2 x i64> @llvm.x86.ssse3.palign.r.128(<2 x i64> %1, <2 x i64> %0, i8 4) nounwind readnone
   store <2 x i64> %2, <2 x i64>* bitcast ([4 x i32]* @c to <2 x i64>*), align 16
   ret void
 }

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