[AArch64] Tweak truncate costs for some scalable vector types

* We were previously returning an invalid cost when truncating
anything to <vscale x 2 x i1>, which is incorrect since we can
generate perfectly good code for this.

* The costs for truncating legal or unpacked types to predicates
seemed overly optimistic. For example, when truncating
<vscale x 8 x i16> to <vscale x 8 x i1> we typically do
something like

  and z0.h, z0.h, #0x1
  cmpne   p0.h, p0/z, z0.h, #0

I guess it might depend upon whether the input value is
generated in the same block or not and if we can avoid the
inreg zero-extend. However, it feels safe to take the more
conservative cost here.

* The costs for some truncates such as

  trunc <vscale x 2 x i32> %a to <vscale x 2 x i16>

were 1, whereas in actual fact they are free and no instructions
are required. Also, for this

  trunc <vscale x 8 x i32> %a to <vscale x 8 x i16>

it's just a single uzp1 instruction so I reduced the cost to 1.

Author: david-arm

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -2782,22 +2782,39 @@ InstructionCost AArch64TTIImpl::getCastInstrCost(unsigned Opcode, Type *Dst,
       {ISD::TRUNCATE, MVT::v16i32, MVT::v16i64, 4}, // 4 x uzp1
 
       // Truncations on nxvmiN
-      {ISD::TRUNCATE, MVT::nxv2i1, MVT::nxv2i16, 1},
-      {ISD::TRUNCATE, MVT::nxv2i1, MVT::nxv2i32, 1},
-      {ISD::TRUNCATE, MVT::nxv2i1, MVT::nxv2i64, 1},
-      {ISD::TRUNCATE, MVT::nxv4i1, MVT::nxv4i16, 1},
-      {ISD::TRUNCATE, MVT::nxv4i1, MVT::nxv4i32, 1},
-      {ISD::TRUNCATE, MVT::nxv4i1, MVT::nxv4i64, 2},
-      {ISD::TRUNCATE, MVT::nxv8i1, MVT::nxv8i16, 1},
-      {ISD::TRUNCATE, MVT::nxv8i1, MVT::nxv8i32, 3},
-      {ISD::TRUNCATE, MVT::nxv8i1, MVT::nxv8i64, 5},
-      {ISD::TRUNCATE, MVT::nxv16i1, MVT::nxv16i8, 1},
-      {ISD::TRUNCATE, MVT::nxv2i16, MVT::nxv2i32, 1},
-      {ISD::TRUNCATE, MVT::nxv2i32, MVT::nxv2i64, 1},
-      {ISD::TRUNCATE, MVT::nxv4i16, MVT::nxv4i32, 1},
-      {ISD::TRUNCATE, MVT::nxv4i32, MVT::nxv4i64, 2},
-      {ISD::TRUNCATE, MVT::nxv8i16, MVT::nxv8i32, 3},
-      {ISD::TRUNCATE, MVT::nxv8i32, MVT::nxv8i64, 6},
+      {ISD::TRUNCATE, MVT::nxv2i1, MVT::nxv2i8,  2},
+      {ISD::TRUNCATE, MVT::nxv2i1, MVT::nxv2i16, 2},
+      {ISD::TRUNCATE, MVT::nxv2i1, MVT::nxv2i32, 2},
+      {ISD::TRUNCATE, MVT::nxv2i1, MVT::nxv2i64, 2},
+      {ISD::TRUNCATE, MVT::nxv4i1, MVT::nxv4i8,  2},
+      {ISD::TRUNCATE, MVT::nxv4i1, MVT::nxv4i16, 2},
+      {ISD::TRUNCATE, MVT::nxv4i1, MVT::nxv4i32, 2},
+      {ISD::TRUNCATE, MVT::nxv4i1, MVT::nxv4i64, 5},
+      {ISD::TRUNCATE, MVT::nxv8i1, MVT::nxv8i8,  2},
+      {ISD::TRUNCATE, MVT::nxv8i1, MVT::nxv8i16, 2},
+      {ISD::TRUNCATE, MVT::nxv8i1, MVT::nxv8i32, 5},
+      {ISD::TRUNCATE, MVT::nxv8i1, MVT::nxv8i64, 11},
+      {ISD::TRUNCATE, MVT::nxv16i1, MVT::nxv16i8, 2},
+      {ISD::TRUNCATE, MVT::nxv2i8, MVT::nxv2i16, 0},
+      {ISD::TRUNCATE, MVT::nxv2i8, MVT::nxv2i32, 0},
+      {ISD::TRUNCATE, MVT::nxv2i8, MVT::nxv2i64, 0},
+      {ISD::TRUNCATE, MVT::nxv2i16, MVT::nxv2i32, 0},
+      {ISD::TRUNCATE, MVT::nxv2i16, MVT::nxv2i64, 0},
+      {ISD::TRUNCATE, MVT::nxv2i32, MVT::nxv2i64, 0},
+      {ISD::TRUNCATE, MVT::nxv4i8, MVT::nxv4i16, 0},
+      {ISD::TRUNCATE, MVT::nxv4i8, MVT::nxv4i32, 0},
+      {ISD::TRUNCATE, MVT::nxv4i8, MVT::nxv4i64, 1},
+      {ISD::TRUNCATE, MVT::nxv4i16, MVT::nxv4i32, 0},
+      {ISD::TRUNCATE, MVT::nxv4i16, MVT::nxv4i64, 1},
+      {ISD::TRUNCATE, MVT::nxv4i32, MVT::nxv4i64, 1},
+      {ISD::TRUNCATE, MVT::nxv8i8, MVT::nxv8i16, 0},
+      {ISD::TRUNCATE, MVT::nxv8i8, MVT::nxv8i32, 1},
+      {ISD::TRUNCATE, MVT::nxv8i8, MVT::nxv8i64, 3},
+      {ISD::TRUNCATE, MVT::nxv8i16, MVT::nxv8i32, 1},
+      {ISD::TRUNCATE, MVT::nxv8i16, MVT::nxv8i64, 3},
+      {ISD::TRUNCATE, MVT::nxv16i8, MVT::nxv16i16, 1},
+      {ISD::TRUNCATE, MVT::nxv16i8, MVT::nxv16i32, 3},
+      {ISD::TRUNCATE, MVT::nxv16i8, MVT::nxv16i64, 7},
 
       // The number of shll instructions for the extension.
       {ISD::SIGN_EXTEND, MVT::v4i64, MVT::v4i16, 3},

llvm/test/Analysis/CostModel/AArch64/sve-cast.ll

@@ -418,27 +418,27 @@ define void @trunc() {
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s2i8i16 = trunc <2 x i16> undef to <2 x i8>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s2i8i32 = trunc <2 x i32> undef to <2 x i8>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s2i8i64 = trunc <2 x i64> undef to <2 x i8>
-; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s2i16i32 = trunc <2 x i32> undef to <2 x i16>
+; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s2i16i32 = trunc <2 x i32> undef to <2 x i16>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s2i16i64 = trunc <2 x i64> undef to <2 x i16>
-; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s2i32i64 = trunc <2 x i64> undef to <2 x i32>
+; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s2i32i64 = trunc <2 x i64> undef to <2 x i32>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i8i16 = trunc <4 x i16> undef to <4 x i8>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i8i32 = trunc <4 x i32> undef to <4 x i8>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i8i64 = trunc <4 x i64> undef to <4 x i8>
-; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s4i16i32 = trunc <4 x i32> undef to <4 x i16>
+; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i16i32 = trunc <4 x i32> undef to <4 x i16>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i16i64 = trunc <4 x i64> undef to <4 x i16>
-; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %s4i32i64 = trunc <4 x i64> undef to <4 x i32>
+; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i32i64 = trunc <4 x i64> undef to <4 x i32>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i8i16 = trunc <8 x i16> undef to <8 x i8>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i8i32 = trunc <8 x i32> undef to <8 x i8>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i8i64 = trunc <8 x i64> undef to <8 x i8>
-; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %s8i16i32 = trunc <8 x i32> undef to <8 x i16>
+; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i16i32 = trunc <8 x i32> undef to <8 x i16>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i16i64 = trunc <8 x i64> undef to <8 x i16>
-; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %s8i32i64 = trunc <8 x i64> undef to <8 x i32>
+; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i32i64 = trunc <8 x i64> undef to <8 x i32>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i8i16 = trunc <16 x i16> undef to <16 x i8>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i8i32 = trunc <16 x i32> undef to <16 x i8>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i8i64 = trunc <16 x i64> undef to <16 x i8>
-; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %s16i16i32 = trunc <16 x i32> undef to <16 x i16>
+; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i16i32 = trunc <16 x i32> undef to <16 x i16>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i16i64 = trunc <16 x i64> undef to <16 x i16>
-; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %s16i32i64 = trunc <16 x i64> undef to <16 x i32>
+; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i32i64 = trunc <16 x i64> undef to <16 x i32>
 ; SVE128-NO-NEON-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
 ; FIXED-MIN-256-LABEL: 'trunc'
@@ -463,19 +463,19 @@ define void @trunc() {
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i8i64 = trunc <4 x i64> undef to <4 x i8>
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s4i16i32 = trunc <4 x i32> undef to <4 x i16>
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i16i64 = trunc <4 x i64> undef to <4 x i16>
-; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s4i32i64 = trunc <4 x i64> undef to <4 x i32>
+; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i32i64 = trunc <4 x i64> undef to <4 x i32>
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s8i8i16 = trunc <8 x i16> undef to <8 x i8>
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i8i32 = trunc <8 x i32> undef to <8 x i8>
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i8i64 = trunc <8 x i64> undef to <8 x i8>
-; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s8i16i32 = trunc <8 x i32> undef to <8 x i16>
+; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i16i32 = trunc <8 x i32> undef to <8 x i16>
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i16i64 = trunc <8 x i64> undef to <8 x i16>
-; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %s8i32i64 = trunc <8 x i64> undef to <8 x i32>
+; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i32i64 = trunc <8 x i64> undef to <8 x i32>
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i8i16 = trunc <16 x i16> undef to <16 x i8>
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i8i32 = trunc <16 x i32> undef to <16 x i8>
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i8i64 = trunc <16 x i64> undef to <16 x i8>
-; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %s16i16i32 = trunc <16 x i32> undef to <16 x i16>
+; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i16i32 = trunc <16 x i32> undef to <16 x i16>
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i16i64 = trunc <16 x i64> undef to <16 x i16>
-; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %s16i32i64 = trunc <16 x i64> undef to <16 x i32>
+; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i32i64 = trunc <16 x i64> undef to <16 x i32>
 ; FIXED-MIN-256-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
 ; FIXED-MIN-2048-LABEL: 'trunc'
@@ -500,19 +500,19 @@ define void @trunc() {
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i8i64 = trunc <4 x i64> undef to <4 x i8>
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s4i16i32 = trunc <4 x i32> undef to <4 x i16>
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i16i64 = trunc <4 x i64> undef to <4 x i16>
-; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s4i32i64 = trunc <4 x i64> undef to <4 x i32>
+; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s4i32i64 = trunc <4 x i64> undef to <4 x i32>
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s8i8i16 = trunc <8 x i16> undef to <8 x i8>
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i8i32 = trunc <8 x i32> undef to <8 x i8>
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i8i64 = trunc <8 x i64> undef to <8 x i8>
-; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s8i16i32 = trunc <8 x i32> undef to <8 x i16>
+; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i16i32 = trunc <8 x i32> undef to <8 x i16>
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i16i64 = trunc <8 x i64> undef to <8 x i16>
-; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s8i32i64 = trunc <8 x i64> undef to <8 x i32>
+; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s8i32i64 = trunc <8 x i64> undef to <8 x i32>
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i8i16 = trunc <16 x i16> undef to <16 x i8>
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i8i32 = trunc <16 x i32> undef to <16 x i8>
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i8i64 = trunc <16 x i64> undef to <16 x i8>
-; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s16i16i32 = trunc <16 x i32> undef to <16 x i16>
+; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i16i32 = trunc <16 x i32> undef to <16 x i16>
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i16i64 = trunc <16 x i64> undef to <16 x i16>
-; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %s16i32i64 = trunc <16 x i64> undef to <16 x i32>
+; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %s16i32i64 = trunc <16 x i64> undef to <16 x i32>
 ; FIXED-MIN-2048-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
   %r8 = trunc i8 undef to i1