[GlobalISel] Enable copy-propagation in post-legalizer combiner

[aemerson]

Summary

This cleans up copies that the legalizer or other combines leave around. They can occasionally end up escaping as moves.

[paquette]

LGTM

llvm/lib/Target/AArch64/AArch64Combine.td

 >;
 
 // Combines which replace a G_SHUFFLE_VECTOR with a target-specific pseudo
 // instruction.
 def shuffle_vector_pseudos : GICombineGroup<[dup, rev, ext, zip, uzp, trn]>;
 
 def AArch64PostLegalizerCombinerHelper
     : GICombinerHelper<"AArch64GenPostLegalizerCombinerHelper",
-                       [erase_undef_store, combines_for_extload,
+                       [copy_prop, erase_undef_store, combines_for_extload,
                         sext_trunc_sextload, shuffle_vector_pseudos,
                         hoist_logic_op_with_same_opcode_hands]> {
   let DisableRuleOption = "aarch64postlegalizercombiner-disable-rule";
 }

llvm/test/CodeGen/AArch64/GlobalISel/combine-sext-trunc-sextload.mir

 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
 # RUN: llc -mtriple aarch64 -run-pass=aarch64-postlegalizer-combiner -verify-machineinstrs %s -o - | FileCheck %s
 ---
 name:            test_combine_sext_trunc_of_sextload
 legalized:       true
 tracksRegLiveness: true
 body: |
   bb.0.entry:
     liveins: $x0
     ; CHECK-LABEL: name: test_combine_sext_trunc_of_sextload
     ; CHECK: liveins: $x0
     ; CHECK: [[COPY:%[0-9]+]]:_(p0) = COPY $x0
     ; CHECK: [[SEXTLOAD:%[0-9]+]]:_(s64) = G_SEXTLOAD [[COPY]](p0) :: (load 2)
     ; CHECK: [[TRUNC:%[0-9]+]]:_(s32) = G_TRUNC [[SEXTLOAD]](s64)
-    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY [[TRUNC]](s32)
-    ; CHECK: $w0 = COPY [[COPY1]](s32)
+    ; CHECK: $w0 = COPY [[TRUNC]](s32)
     %0:_(p0) = COPY $x0
     %1:_(s64) = G_SEXTLOAD %0:_(p0) :: (load 2)
     %2:_(s32) = G_TRUNC %1:_(s64)
     %3:_(s32) = G_SEXT_INREG %2:_(s32), 16
     $w0 = COPY %3(s32)
 ...
 ---
 name:            test_combine_sext_of_sextload
 legalized:       true
 tracksRegLiveness: true
 body: |
   bb.0.entry:
     liveins: $x0
     ; CHECK-LABEL: name: test_combine_sext_of_sextload
     ; CHECK: liveins: $x0
     ; CHECK: [[COPY:%[0-9]+]]:_(p0) = COPY $x0
     ; CHECK: [[SEXTLOAD:%[0-9]+]]:_(s32) = G_SEXTLOAD [[COPY]](p0) :: (load 2)
-    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY [[SEXTLOAD]](s32)
-    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[COPY1]](s32)
-    ; CHECK: $w0 = COPY [[COPY2]](s32)
+    ; CHECK: $w0 = COPY [[SEXTLOAD]](s32)
     %0:_(p0) = COPY $x0
     %1:_(s32) = G_SEXTLOAD %0:_(p0) :: (load 2)
     %2:_(s32) = COPY %1:_(s32)
     %3:_(s32) = G_SEXT_INREG %2:_(s32), 16
     $w0 = COPY %3(s32)
 ...
 ---
 name:            test_combine_sext_of_sextload_not_matching
 legalized:       true
 tracksRegLiveness: true
 body: |
   bb.0.entry:
     liveins: $x0
     ; Here we're trying to extend from a smaller value than was extended in the load.
     ; CHECK-LABEL: name: test_combine_sext_of_sextload_not_matching
     ; CHECK: liveins: $x0
     ; CHECK: [[COPY:%[0-9]+]]:_(p0) = COPY $x0
     ; CHECK: [[SEXTLOAD:%[0-9]+]]:_(s32) = G_SEXTLOAD [[COPY]](p0) :: (load 2)
-    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY [[SEXTLOAD]](s32)
-    ; CHECK: [[SEXT_INREG:%[0-9]+]]:_(s32) = G_SEXT_INREG [[COPY1]], 24
+    ; CHECK: [[SEXT_INREG:%[0-9]+]]:_(s32) = G_SEXT_INREG [[SEXTLOAD]], 24
     ; CHECK: $w0 = COPY [[SEXT_INREG]](s32)
     %0:_(p0) = COPY $x0
     %1:_(s32) = G_SEXTLOAD %0:_(p0) :: (load 2)
     %2:_(s32) = COPY %1:_(s32)
     %3:_(s32) = G_SEXT_INREG %2:_(s32), 24
     $w0 = COPY %3(s32)
 ...

llvm/test/CodeGen/AArch64/GlobalISel/postlegalizer-combiner-copy-prop.mir

+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple aarch64 -run-pass=aarch64-postlegalizer-combiner -verify-machineinstrs %s -o - | FileCheck %s
+
+...
+---
+name:            postlegalize_copy_prop
+legalized:       true
+tracksRegLiveness: true
+body:             |
+  bb.1.entry:
+    liveins: $x0, $x1
+
+    ; CHECK-LABEL: name: postlegalize_copy_prop
+    ; CHECK: liveins: $x0, $x1
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s64) = COPY $x1
+    ; CHECK: [[ADD:%[0-9]+]]:_(s64) = G_ADD [[COPY]], [[COPY1]]
+    ; CHECK: [[ADD1:%[0-9]+]]:_(s64) = G_ADD [[ADD]], [[ADD]]
+    ; CHECK: $x0 = COPY [[ADD1]](s64)
+    ; CHECK: RET_ReallyLR
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %2:_(s64) = G_ADD %0, %1
+    %3:_(s64) = COPY %2
+    %4:_(s64) = G_ADD %3, %3
+    $x0 = COPY %4
+    RET_ReallyLR
+
+...