[AArch64][GlobalISel] Basic add_sat and sub_sat vector handling.

This tries to fill in the basic vector handling for sadd_sat/uadd_sat and
ssub_sat/usub_sat. It just handles the basics, marking legal types and clamping
illegally sized vectors to legal ones.

Author: davemgreen

llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp

@@ -1103,9 +1103,6 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST)
       .scalarize(1)
       .lower();
 
-  getActionDefinitionsBuilder({G_UADDSAT, G_USUBSAT})
-      .lowerIf([=](const LegalityQuery &Q) { return Q.Types[0].isScalar(); });
-
   getActionDefinitionsBuilder({G_FSHL, G_FSHR})
       .customFor({{s32, s32}, {s32, s64}, {s64, s64}})
       .lower();
@@ -1153,8 +1150,14 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST)
       .minScalarEltSameAsIf(always, 1, 0)
       .maxScalarEltSameAsIf(always, 1, 0);
 
-  // TODO: Vector types.
-  getActionDefinitionsBuilder({G_SADDSAT, G_SSUBSAT}).lowerIf(isScalar(0));
+  getActionDefinitionsBuilder({G_UADDSAT, G_SADDSAT, G_USUBSAT, G_SSUBSAT})
+      .legalFor({v2s64, v2s32, v4s32, v4s16, v8s16, v8s8, v16s8})
+      .clampNumElements(0, v8s8, v16s8)
+      .clampNumElements(0, v4s16, v8s16)
+      .clampNumElements(0, v2s32, v4s32)
+      .clampMaxNumElements(0, s64, 2)
+      .moreElementsToNextPow2(0)
+      .lowerIf(isScalar(0));
 
   // TODO: Libcall support for s128.
   // TODO: s16 should be legal with full FP16 support.

llvm/test/CodeGen/AArch64/GlobalISel/legalizer-info-validation.mir

@@ -392,6 +392,7 @@
 # DEBUG-NEXT: .. type index coverage check SKIPPED: user-defined predicate detected
 # DEBUG-NEXT: .. imm index coverage check SKIPPED: user-defined predicate detected
 # DEBUG-NEXT: G_SADDSAT (opcode {{[0-9]+}}): 1 type index, 0 imm indices
+# DEBUG-NEXT: .. opcode {{[0-9]+}} is aliased to {{[0-9]+}}
 # DEBUG-NEXT: .. type index coverage check SKIPPED: user-defined predicate detected
 # DEBUG-NEXT: .. imm index coverage check SKIPPED: user-defined predicate detected
 # DEBUG-NEXT: G_USUBSAT (opcode {{[0-9]+}}): 1 type index, 0 imm indices

llvm/test/CodeGen/AArch64/sadd_sat.ll

@@ -2,8 +2,6 @@
 ; RUN: llc < %s -mtriple=aarch64-- | FileCheck %s --check-prefixes=CHECK,CHECK-SD
 ; RUN: llc < %s -mtriple=aarch64-- -global-isel -global-isel-abort=2 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-GI
 
-; CHECK-GI:       warning: Instruction selection used fallback path for vec
-
 declare i4 @llvm.sadd.sat.i4(i4, i4)
 declare i8 @llvm.sadd.sat.i8(i8, i8)
 declare i16 @llvm.sadd.sat.i16(i16, i16)