[CIR] Use poison as second vector operand in unary shuffles. (#1891)

First noted at: #1829
Also:
Adjusted test cases affected by this change.

---------

Co-authored-by: Tommy MᶜMichen <[email protected]>

Author: RiverDave

clang/lib/CIR/CodeGen/CIRGenBuilder.h

@@ -991,9 +991,11 @@ class CIRGenBuilderTy : public cir::CIRBaseBuilderTy {
 
   cir::VecShuffleOp createVecShuffle(mlir::Location loc, mlir::Value vec1,
                                      llvm::ArrayRef<int64_t> mask) {
-    // FIXME(cir): Support use cir.vec.shuffle with single vec
-    // Workaround: pass Vec as both vec1 and vec2
-    return createVecShuffle(loc, vec1, vec1, mask);
+    /// Create a unary shuffle. The second vector operand of the IR instruction
+    /// is poison.
+    return createVecShuffle(
+        loc, vec1, getConstant(loc, cir::PoisonAttr::get(vec1.getType())),
+        mask);
   }
 
   cir::StoreOp

clang/lib/CIR/CodeGen/CIRGenBuiltinX86.cpp

@@ -1031,13 +1031,8 @@ mlir::Value CIRGenFunction::emitX86BuiltinExpr(unsigned BuiltinID,
     for (unsigned i = 0; i != dstNumElts; ++i)
       indices[i] = (i >= srcNumElts) ? srcNumElts + (i % srcNumElts) : i;
 
-    cir::ConstantOp poisonVec =
-        builder.getConstant(getLoc(E->getExprLoc()),
-                            builder.getAttr<cir::PoisonAttr>(Ops[1].getType()));
-
-    mlir::Value op1 =
-        builder.createVecShuffle(getLoc(E->getExprLoc()), Ops[1], poisonVec,
-                                 ArrayRef(indices, dstNumElts));
+    mlir::Value op1 = builder.createVecShuffle(getLoc(E->getExprLoc()), Ops[1],
+                                               ArrayRef(indices, dstNumElts));
 
     for (unsigned i = 0; i != dstNumElts; ++i) {
       if (i >= index && i < (index + srcNumElts))