[llvm] [GlobalISel] Transform anyext(freeze(trunc(x))) to freeze(x) (PR #165679)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-globalisel

Author: David Green (davemgreen)

<details>
<summary>Changes</summary>

We already have a transform for (anyext (trunc x)) -> x, this adds an extended version for (anyext (freeze (trunc x))) -> (freeze x). As we treat freeze i8 and i16 as legal this can help reduce the number of extends in the code.

---
Full diff: https://github.com/llvm/llvm-project/pull/165679.diff


2 Files Affected:

- (modified) llvm/include/llvm/Target/GlobalISel/Combine.td (+20-8) 
- (modified) llvm/test/CodeGen/AArch64/GlobalISel/combine-ext.mir (+21-4) 


``````````diff
diff --git a/llvm/include/llvm/Target/GlobalISel/Combine.td b/llvm/include/llvm/Target/GlobalISel/Combine.td
index 119695e53c3cb..a102e3f0c6a47 100644
--- a/llvm/include/llvm/Target/GlobalISel/Combine.td
+++ b/llvm/include/llvm/Target/GlobalISel/Combine.td
@@ -805,16 +805,28 @@ def redundant_sext_inreg: GICombineRule <
   (defs root:$root),
   (match (wip_match_opcode G_SEXT_INREG):$root,
          [{ return Helper.matchRedundantSExtInReg(*${root}); }]),
-     (apply [{ Helper.replaceSingleDefInstWithOperand(*${root}, 1); }])
+  (apply [{ Helper.replaceSingleDefInstWithOperand(*${root}, 1); }])
 >;
 
-// Fold (anyext (trunc x)) -> x if the source type is same as
-// the destination type.
+// Fold (anyext (trunc x)) -> x if the source type is same as the destination
+// type.
 def anyext_trunc_fold: GICombineRule <
-  (defs root:$root, register_matchinfo:$matchinfo),
-  (match (wip_match_opcode G_ANYEXT):$root,
-         [{ return Helper.matchCombineAnyExtTrunc(*${root}, ${matchinfo}); }]),
-  (apply [{ Helper.replaceSingleDefInstWithReg(*${root}, ${matchinfo}); }])
+  (defs root:$root),
+  (match (G_TRUNC $x, $src),
+         (G_ANYEXT $dst, $x):$root,
+         [{ return MRI.getType(${dst}.getReg()) == MRI.getType(${src}.getReg()); }]),
+  (apply (GIReplaceReg $dst, $src))
+>;
+
+// Fold (anyext (freeze (trunc x))) -> (freeze x) if the source type is same as
+// the destination type.
+def anyext_freeze_trunc_fold: GICombineRule <
+  (defs root:$root),
+  (match (G_TRUNC $x, $src),
+         (G_FREEZE $y, $x),
+         (G_ANYEXT $dst, $y):$root,
+         [{ return MRI.getType(${dst}.getReg()) == MRI.getType(${src}.getReg()); }]),
+  (apply (G_FREEZE $dst, $src))
 >;
 
 // Fold (zext (trunc x)) -> x if the source type is same as the destination type
@@ -2084,7 +2096,7 @@ def undef_combines : GICombineGroup<[undef_to_fp_zero, undef_to_int_zero,
 def identity_combines : GICombineGroup<[select_same_val, right_identity_zero,
                                         binop_same_val, binop_left_to_zero,
                                         binop_right_to_zero, p2i_to_i2p,
-                                        i2p_to_p2i, anyext_trunc_fold,
+                                        i2p_to_p2i, anyext_trunc_fold, anyext_freeze_trunc_fold,
                                         fneg_fneg_fold, right_identity_one,
                                         add_sub_reg, buildvector_identity_fold,
                                         trunc_buildvector_fold,
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/combine-ext.mir b/llvm/test/CodeGen/AArch64/GlobalISel/combine-ext.mir
index 629238126380c..2b24a8920e0e0 100644
--- a/llvm/test/CodeGen/AArch64/GlobalISel/combine-ext.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/combine-ext.mir
@@ -385,8 +385,8 @@ body:             |
     ; CHECK: liveins: $h0
     ; CHECK-NEXT: {{  $}}
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s16) = COPY $h0
-    ; CHECK-NEXT: %2:_(s64) = nneg G_ZEXT [[COPY]](s16)
-    ; CHECK-NEXT: $x0 = COPY %2(s64)
+    ; CHECK-NEXT: [[ZEXT:%[0-9]+]]:_(s64) = nneg G_ZEXT [[COPY]](s16)
+    ; CHECK-NEXT: $x0 = COPY [[ZEXT]](s64)
     %0:_(s16) = COPY $h0
     %1:_(s32) = G_ANYEXT %0(s16)
     %2:_(s64) = nneg G_ZEXT %1(s32)
@@ -401,10 +401,27 @@ body:             |
     ; CHECK: liveins: $h0
     ; CHECK-NEXT: {{  $}}
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s16) = COPY $h0
-    ; CHECK-NEXT: %2:_(s64) = nneg G_ZEXT [[COPY]](s16)
-    ; CHECK-NEXT: $x0 = COPY %2(s64)
+    ; CHECK-NEXT: [[ZEXT:%[0-9]+]]:_(s64) = nneg G_ZEXT [[COPY]](s16)
+    ; CHECK-NEXT: $x0 = COPY [[ZEXT]](s64)
     %0:_(s16) = COPY $h0
     %1:_(s32) = nneg G_ZEXT %0(s16)
     %2:_(s64) = G_ANYEXT %1(s32)
     $x0 = COPY %2(s64)
 ...
+---
+name:            test_combine_anyext_freeze_trunc
+body:             |
+  bb.1:
+  liveins: $x0
+    ; CHECK-LABEL: name: test_combine_anyext_freeze_trunc
+    ; CHECK: liveins: $x0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK-NEXT: [[FREEZE:%[0-9]+]]:_(s64) = G_FREEZE [[COPY]]
+    ; CHECK-NEXT: $x1 = COPY [[FREEZE]](s64)
+    %0:_(s64) = COPY $x0
+    %1:_(s32) = G_TRUNC %0(s64)
+    %2:_(s32) = G_FREEZE %1(s32)
+    %3:_(s64) = G_ANYEXT %2(s32)
+    $x1 = COPY %3(s64)
+...

``````````

</details>


https://github.com/llvm/llvm-project/pull/165679