add splat vector

Author: Thorsten Schütt

llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp

@@ -64,8 +64,11 @@ KnownBits GISelKnownBits::getKnownBits(MachineInstr &MI) {
 
 KnownBits GISelKnownBits::getKnownBits(Register R) {
   const LLT Ty = MRI.getType(R);
+  // Since the number of lanes in a scalable vector is unknown at compile time,
+  // we track one bit which is implicitly broadcast to all lanes.  This means
+  // that all lanes in a scalable vector are considered demanded.
   APInt DemandedElts =
-      Ty.isVector() ? APInt::getAllOnes(Ty.getNumElements()) : APInt(1, 1);
+      Ty.isFixedVector() ? APInt::getAllOnes(Ty.getNumElements()) : APInt(1, 1);
   return getKnownBits(R, DemandedElts);
 }
 

llvm/test/CodeGen/AArch64/GlobalISel/combine-with-flags.mir

@@ -271,3 +271,21 @@ body:             |
     %z:_(<2 x s32>) = G_ZEXT  %t
     $d0 = COPY %z
 ...
+---
+name:            zext_trunc_nuw_scalable_vector
+body:             |
+  bb.0:
+    liveins: $w0, $w1
+    ; CHECK-LABEL: name: zext_trunc_nuw_scalable_vector
+    ; CHECK: liveins: $w0, $w1
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK-NEXT: %sv0:_(<vscale x 2 x s64>) = G_SPLAT_VECTOR [[COPY]](s64)
+    ; CHECK-NEXT: $z0 = COPY %sv0(<vscale x 2 x s64>)
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %sv0:_(<vscale x 2 x s64>) = G_SPLAT_VECTOR %0:_(s64)
+    %t:_(<vscale x 2 x s32>) = nuw G_TRUNC %sv0
+    %z:_(<vscale x 2 x s64>) = G_ZEXT  %t
+    $z0 = COPY %z
+...