[GlobalISel][AArch64] Legalize vector G_SELECT

[paquette]

Summary

Just scalarize it, and add a test showing it works.

[aemerson]

LGTM, though eventually we might want to change scalarizations to more efficient expansion lowerings.

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

getActionDefinitionsBuilder({G_SITOFP, G_UITOFP})
       .clampScalar(0, s32, s64)
       .widenScalarToNextPow2(0);
 
   // Control-flow
   getActionDefinitionsBuilder(G_BRCOND).legalFor({s1, s8, s16, s32});
   getActionDefinitionsBuilder(G_BRINDIRECT).legalFor({p0});
 
   // Select
+  // FIXME: We can probably do a bit better than just scalarizing vector
+  // selects.
   getActionDefinitionsBuilder(G_SELECT)
       .legalFor({{s32, s1}, {s64, s1}, {p0, s1}})
       .clampScalar(0, s32, s64)
-      .widenScalarToNextPow2(0);
+      .widenScalarToNextPow2(0)
+      .scalarize(0);
 
   // Pointer-handling
   getActionDefinitionsBuilder(G_FRAME_INDEX).legalFor({p0});
   getActionDefinitionsBuilder(G_GLOBAL_VALUE).legalFor({p0});
 
   getActionDefinitionsBuilder(G_PTRTOINT)
       .legalForCartesianProduct({s1, s8, s16, s32, s64}, {p0})
       .maxScalar(0, s64)

llvm/trunk/test/CodeGen/AArch64/GlobalISel/legalize-select.mir

+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc %s -verify-machineinstrs -O0 -run-pass=legalizer -mtriple aarch64-unknown-unknown -o - | FileCheck %s
+...
+---
+name:            v2s64
+alignment:       2
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $q0, $q1
+
+    ; CHECK-LABEL: name: v2s64
+    ; CHECK: liveins: $q0, $q1
+    ; CHECK: [[COPY:%[0-9]+]]:_(<2 x s64>) = COPY $q0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(<2 x s64>) = COPY $q1
+    ; CHECK: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 0
+    ; CHECK: [[BUILD_VECTOR:%[0-9]+]]:_(<2 x s64>) = G_BUILD_VECTOR [[C]](s64), [[C]](s64)
+    ; CHECK: [[ICMP:%[0-9]+]]:_(<2 x s1>) = G_ICMP intpred(sgt), [[COPY]](<2 x s64>), [[BUILD_VECTOR]]
+    ; CHECK: [[UV:%[0-9]+]]:_(s1), [[UV1:%[0-9]+]]:_(s1) = G_UNMERGE_VALUES [[ICMP]](<2 x s1>)
+    ; CHECK: [[UV2:%[0-9]+]]:_(s64), [[UV3:%[0-9]+]]:_(s64) = G_UNMERGE_VALUES [[COPY1]](<2 x s64>)
+    ; CHECK: [[UV4:%[0-9]+]]:_(s64), [[UV5:%[0-9]+]]:_(s64) = G_UNMERGE_VALUES [[COPY]](<2 x s64>)
+    ; CHECK: [[SELECT:%[0-9]+]]:_(s64) = G_SELECT [[UV]](s1), [[UV2]], [[UV4]]
+    ; CHECK: [[SELECT1:%[0-9]+]]:_(s64) = G_SELECT [[UV1]](s1), [[UV3]], [[UV5]]
+    ; CHECK: [[BUILD_VECTOR1:%[0-9]+]]:_(<2 x s64>) = G_BUILD_VECTOR [[SELECT]](s64), [[SELECT1]](s64)
+    ; CHECK: $q0 = COPY [[BUILD_VECTOR1]](<2 x s64>)
+    ; CHECK: RET_ReallyLR implicit $q0
+    %0:_(<2 x s64>) = COPY $q0
+    %1:_(<2 x s64>) = COPY $q1
+    %3:_(s64) = G_CONSTANT i64 0
+    %2:_(<2 x s64>) = G_BUILD_VECTOR %3(s64), %3(s64)
+    %4:_(<2 x s1>) = G_ICMP intpred(sgt), %0(<2 x s64>), %2
+    %5:_(<2 x s64>) = G_SELECT %4(<2 x s1>), %1, %0
+    $q0 = COPY %5(<2 x s64>)
+    RET_ReallyLR implicit $q0
+
+...
+---
+name:            v2s32
+alignment:       2
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $d0, $d1
+
+    ; CHECK-LABEL: name: v2s32
+    ; CHECK: liveins: $d0, $d1
+    ; CHECK: [[COPY:%[0-9]+]]:_(<2 x s32>) = COPY $d0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(<2 x s32>) = COPY $d1
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; CHECK: [[BUILD_VECTOR:%[0-9]+]]:_(<2 x s32>) = G_BUILD_VECTOR [[C]](s32), [[C]](s32)
+    ; CHECK: [[ICMP:%[0-9]+]]:_(<2 x s1>) = G_ICMP intpred(sgt), [[COPY]](<2 x s32>), [[BUILD_VECTOR]]
+    ; CHECK: [[UV:%[0-9]+]]:_(s1), [[UV1:%[0-9]+]]:_(s1) = G_UNMERGE_VALUES [[ICMP]](<2 x s1>)
+    ; CHECK: [[UV2:%[0-9]+]]:_(s32), [[UV3:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES [[COPY1]](<2 x s32>)
+    ; CHECK: [[UV4:%[0-9]+]]:_(s32), [[UV5:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES [[COPY]](<2 x s32>)
+    ; CHECK: [[SELECT:%[0-9]+]]:_(s32) = G_SELECT [[UV]](s1), [[UV2]], [[UV4]]
+    ; CHECK: [[SELECT1:%[0-9]+]]:_(s32) = G_SELECT [[UV1]](s1), [[UV3]], [[UV5]]
+    ; CHECK: [[BUILD_VECTOR1:%[0-9]+]]:_(<2 x s32>) = G_BUILD_VECTOR [[SELECT]](s32), [[SELECT1]](s32)
+    ; CHECK: $d0 = COPY [[BUILD_VECTOR1]](<2 x s32>)
+    ; CHECK: RET_ReallyLR implicit $d0
+    %0:_(<2 x s32>) = COPY $d0
+    %1:_(<2 x s32>) = COPY $d1
+    %3:_(s32) = G_CONSTANT i32 0
+    %2:_(<2 x s32>) = G_BUILD_VECTOR %3(s32), %3(s32)
+    %4:_(<2 x s1>) = G_ICMP intpred(sgt), %0(<2 x s32>), %2
+    %5:_(<2 x s32>) = G_SELECT %4(<2 x s1>), %1, %0
+    $d0 = COPY %5(<2 x s32>)
+    RET_ReallyLR implicit $d0
+
+...