[LLVM][IR] Add textual shorthand for specifying constant vector splats. (#74620)

Add LL parsing for `<N x ty> splat(ty <imm>)` that lowers onto
ConstantInt::get() for integer types and ConstantFP::get() for
floating-point types.

The intent is to extend ConstantInt/FP classes to support vector types
rather than redirecting to other constant classes as the get() methods
do today.

This patch gives IR writers the convenience of using the shorthand
today, thus allowing existing tests to be ported.

Author: paulwalker-arm

llvm/docs/LangRef.rst

@@ -4299,6 +4299,11 @@ constants and smaller complex constants.
     "``< i32 42, i32 11, i32 74, i32 100 >``". Vector constants
     must have :ref:`vector type <t_vector>`, and the number and types of
     elements must match those specified by the type.
+
+    When creating a vector whose elements have the same constant value, the
+    preferred syntax is ``splat (<Ty> Val)``. For example: "``splat (i32 11)``".
+    These vector constants must have ::ref:`vector type <t_vector>` with an
+    element type that matches the ``splat`` operand.
 **Zero initialization**
     The string '``zeroinitializer``' can be used to zero initialize a
     value to zero of *any* type, including scalar and

llvm/include/llvm/AsmParser/LLParser.h

@@ -64,6 +64,7 @@ namespace llvm {
       t_Poison,              // No value.
       t_EmptyArray,          // No value:  []
       t_Constant,            // Value in ConstantVal.
+      t_ConstantSplat,       // Value in ConstantVal.
       t_InlineAsm,           // Value in FTy/StrVal/StrVal2/UIntVal.
       t_ConstantStruct,      // Value in ConstantStructElts.
       t_PackedConstantStruct // Value in ConstantStructElts.

llvm/include/llvm/AsmParser/LLToken.h

@@ -336,6 +336,7 @@ enum Kind {
   kw_extractelement,
   kw_insertelement,
   kw_shufflevector,
+  kw_splat,
   kw_extractvalue,
   kw_insertvalue,
   kw_blockaddress,

llvm/lib/AsmParser/LLLexer.cpp

@@ -698,6 +698,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(uinc_wrap);
   KEYWORD(udec_wrap);
 
+  KEYWORD(splat);
   KEYWORD(vscale);
   KEYWORD(x);
   KEYWORD(blockaddress);

llvm/lib/AsmParser/LLParser.cpp

@@ -3981,6 +3981,21 @@ bool LLParser::parseValID(ValID &ID, PerFunctionState *PFS, Type *ExpectedTy) {
     return false;
   }
 
+  case lltok::kw_splat: {
+    Lex.Lex();
+    if (parseToken(lltok::lparen, "expected '(' after vector splat"))
+      return true;
+    Constant *C;
+    if (parseGlobalTypeAndValue(C))
+      return true;
+    if (parseToken(lltok::rparen, "expected ')' at end of vector splat"))
+      return true;
+
+    ID.ConstantVal = C;
+    ID.Kind = ValID::t_ConstantSplat;
+    return false;
+  }
+
   case lltok::kw_getelementptr:
   case lltok::kw_shufflevector:
   case lltok::kw_insertelement:
@@ -5824,6 +5839,17 @@ bool LLParser::convertValIDToValue(Type *Ty, ValID &ID, Value *&V,
                                "' but expected '" + getTypeString(Ty) + "'");
     V = ID.ConstantVal;
     return false;
+  case ValID::t_ConstantSplat:
+    if (!Ty->isVectorTy())
+      return error(ID.Loc, "vector constant must have vector type");
+    if (ID.ConstantVal->getType() != Ty->getScalarType())
+      return error(ID.Loc, "constant expression type mismatch: got type '" +
+                               getTypeString(ID.ConstantVal->getType()) +
+                               "' but expected '" +
+                               getTypeString(Ty->getScalarType()) + "'");
+    V = ConstantVector::getSplat(cast<VectorType>(Ty)->getElementCount(),
+                                 ID.ConstantVal);
+    return false;
   case ValID::t_ConstantStruct:
   case ValID::t_PackedConstantStruct:
     if (StructType *ST = dyn_cast<StructType>(Ty)) {
@@ -5861,6 +5887,7 @@ bool LLParser::parseConstantValue(Type *Ty, Constant *&C) {
   case ValID::t_APFloat:
   case ValID::t_Undef:
   case ValID::t_Constant:
+  case ValID::t_ConstantSplat:
   case ValID::t_ConstantStruct:
   case ValID::t_PackedConstantStruct: {
     Value *V;

llvm/test/Assembler/constant-splat-diagnostics.ll

@@ -0,0 +1,40 @@
+; RUN: rm -rf %t && split-file %s %t
+
+; RUN: not llvm-as < %t/not_a_constant.ll -o /dev/null 2>&1 | FileCheck -check-prefix=NOT_A_CONSTANT %s
+; RUN: not llvm-as < %t/not_a_sclar.ll -o /dev/null 2>&1 | FileCheck -check-prefix=NOT_A_SCALAR %s
+; RUN: not llvm-as < %t/not_a_vector.ll -o /dev/null 2>&1 | FileCheck -check-prefix=NOT_A_VECTOR %s
+; RUN: not llvm-as < %t/wrong_explicit_type.ll -o /dev/null 2>&1 | FileCheck -check-prefix=WRONG_EXPLICIT_TYPE %s
+; RUN: not llvm-as < %t/wrong_implicit_type.ll -o /dev/null 2>&1 | FileCheck -check-prefix=WRONG_IMPLICIT_TYPE %s
+
+;--- not_a_constant.ll
+; NOT_A_CONSTANT: error: expected instruction opcode
+define <4 x i32> @not_a_constant(i32 %a) {
+  %splat = splat (i32 %a)
+  ret <vscale x 4 x i32> %splat
+}
+
+;--- not_a_sclar.ll
+; NOT_A_SCALAR: error: constant expression type mismatch: got type '<1 x i32>' but expected 'i32'
+define <4 x i32> @not_a_scalar() {
+  ret <4 x i32> splat (<1 x i32> <i32 7>)
+}
+
+;--- not_a_vector.ll
+; NOT_A_VECTOR: error: vector constant must have vector type
+define <4 x i32> @not_a_vector() {
+  ret i32 splat (i32 7)
+}
+
+;--- wrong_explicit_type.ll
+; WRONG_EXPLICIT_TYPE: error: constant expression type mismatch: got type 'i8' but expected 'i32'
+define <4 x i32> @wrong_explicit_type() {
+  ret <4 x i32> splat (i8 7)
+}
+
+;--- wrong_implicit_type.ll
+; WRONG_IMPLICIT_TYPE: error: constant expression type mismatch: got type 'i8' but expected 'i32'
+define void @wrong_implicit_type(<4 x i32> %a) {
+  %add = add <4 x i32> %a, splat (i8 7)
+  ret void
+}
+

llvm/test/Assembler/constant-splat.ll

@@ -0,0 +1,67 @@
+; RUN: llvm-as < %s | llvm-dis | llvm-as | llvm-dis | FileCheck %s
+
+; NOTE: Tests the expansion of the "splat" shorthand method to create vector
+; constants.  Future work will change how "splat" is expanded, ultimately
+; leading to a point where "splat" is emitted as the disassembly.
+
+@my_global = external global i32
+
+; CHECK: @constant.splat.i1 = constant <1 x i1> <i1 true>
+@constant.splat.i1 = constant <1 x i1> splat (i1 true)
+
+; CHECK: @constant.splat.i32 = constant <5 x i32> <i32 7, i32 7, i32 7, i32 7, i32 7>
+@constant.splat.i32 = constant <5 x i32> splat (i32 7)
+
+; CHECK: @constant.splat.i128 = constant <2 x i128> <i128 85070591730234615870450834276742070272, i128 85070591730234615870450834276742070272>
+@constant.splat.i128 = constant <2 x i128> splat (i128 85070591730234615870450834276742070272)
+
+; CHECK: @constant.splat.f16 = constant <4 x half> <half 0xHBC00, half 0xHBC00, half 0xHBC00, half 0xHBC00>
+@constant.splat.f16 = constant <4 x half> splat (half 0xHBC00)
+
+; CHECK: @constant.splat.f32 = constant <5 x float> <float -2.000000e+00, float -2.000000e+00, float -2.000000e+00, float -2.000000e+00, float -2.000000e+00>
+@constant.splat.f32 = constant <5 x float> splat (float -2.000000e+00)
+
+; CHECK: @constant.splat.f64 = constant <3 x double> <double -3.000000e+00, double -3.000000e+00, double -3.000000e+00>
+@constant.splat.f64 = constant <3 x double> splat (double -3.000000e+00)
+
+; CHECK: @constant.splat.128 = constant <2 x fp128> <fp128 0xL00000000000000018000000000000000, fp128 0xL00000000000000018000000000000000>
+@constant.splat.128 = constant <2 x fp128> splat (fp128 0xL00000000000000018000000000000000)
+
+; CHECK: @constant.splat.bf16 = constant <4 x bfloat> <bfloat 0xRC0A0, bfloat 0xRC0A0, bfloat 0xRC0A0, bfloat 0xRC0A0>
+@constant.splat.bf16 = constant <4 x bfloat> splat (bfloat 0xRC0A0)
+
+; CHECK: @constant.splat.x86_fp80 = constant <3 x x86_fp80> <x86_fp80 0xK4000C8F5C28F5C28F800, x86_fp80 0xK4000C8F5C28F5C28F800, x86_fp80 0xK4000C8F5C28F5C28F800>
+@constant.splat.x86_fp80 = constant <3 x x86_fp80> splat (x86_fp80 0xK4000C8F5C28F5C28F800)
+
+; CHECK: @constant.splat.ppc_fp128 = constant <1 x ppc_fp128> <ppc_fp128 0xM80000000000000000000000000000000>
+@constant.splat.ppc_fp128 = constant <1 x ppc_fp128> splat (ppc_fp128 0xM80000000000000000000000000000000)
+
+; CHECK: @constant.splat.global.ptr = constant <4 x ptr> <ptr @my_global, ptr @my_global, ptr @my_global, ptr @my_global>
+@constant.splat.global.ptr = constant <4 x ptr> splat (ptr @my_global)
+
+define void @add_fixed_lenth_vector_splat_i32(<4 x i32> %a) {
+; CHECK: %add = add <4 x i32> %a, <i32 137, i32 137, i32 137, i32 137>
+  %add = add <4 x i32> %a, splat (i32 137)
+  ret void
+}
+
+define <4 x i32> @ret_fixed_lenth_vector_splat_i32() {
+; CHECK: ret <4 x i32> <i32 56, i32 56, i32 56, i32 56>
+  ret <4 x i32> splat (i32 56)
+}
+
+define void @add_fixed_lenth_vector_splat_double(<vscale x 2 x double> %a) {
+; CHECK: %add = fadd <vscale x 2 x double> %a, shufflevector (<vscale x 2 x double> insertelement (<vscale x 2 x double> poison, double 5.700000e+00, i64 0), <vscale x 2 x double> poison, <vscale x 2 x i32> zeroinitializer)
+  %add = fadd <vscale x 2 x double> %a, splat (double 5.700000e+00)
+  ret void
+}
+
+define <vscale x 4 x i32> @ret_scalable_vector_splat_i32() {
+; CHECK: ret <vscale x 4 x i32> shufflevector (<vscale x 4 x i32> insertelement (<vscale x 4 x i32> poison, i32 78, i64 0), <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer)
+  ret <vscale x 4 x i32> splat (i32 78)
+}
+
+define <vscale x 4 x ptr> @ret_scalable_vector_ptr() {
+; CHECK: ret <vscale x 4 x ptr> shufflevector (<vscale x 4 x ptr> insertelement (<vscale x 4 x ptr> poison, ptr @my_global, i64 0), <vscale x 4 x ptr> poison, <vscale x 4 x i32> zeroinitializer)
+  ret <vscale x 4 x ptr> splat (ptr @my_global)
+}