[llvm] 8aedb43 - [GlobalISel] Combine abs(undef) -> 0
Jessica Paquette via llvm-commits
llvm-commits at lists.llvm.org
Sat Oct 1 15:16:50 PDT 2022
Author: Jessica Paquette
Date: 2022-10-01T15:16:32-07:00
New Revision: 8aedb435db7ef95ded4b68732ce96a5bf92cfd74
URL: https://github.com/llvm/llvm-project/commit/8aedb435db7ef95ded4b68732ce96a5bf92cfd74
DIFF: https://github.com/llvm/llvm-project/commit/8aedb435db7ef95ded4b68732ce96a5bf92cfd74.diff
LOG: [GlobalISel] Combine abs(undef) -> 0
SDAG does this, GISel doesn't.
See https://gcc.godbolt.org/z/sqjMx3Tfv
More context:
https://github.com/llvm/llvm-project/issues/57256
Differential Revision: https://reviews.llvm.org/D135021
Added:
llvm/test/CodeGen/AArch64/GlobalISel/combine-unary-undef-to-zero.mir
Modified:
llvm/include/llvm/Target/GlobalISel/Combine.td
Removed:
################################################################################
diff --git a/llvm/include/llvm/Target/GlobalISel/Combine.td b/llvm/include/llvm/Target/GlobalISel/Combine.td
index add2cd704329..d2868d86741a 100644
--- a/llvm/include/llvm/Target/GlobalISel/Combine.td
+++ b/llvm/include/llvm/Target/GlobalISel/Combine.td
@@ -241,6 +241,12 @@ def binop_right_undef_to_undef: GICombineRule<
[{ return Helper.matchOperandIsUndef(*${root}, 2); }]),
(apply [{ Helper.replaceInstWithUndef(*${root}); }])>;
+def unary_undef_to_zero: GICombineRule<
+ (defs root:$root),
+ (match (wip_match_opcode G_ABS):$root,
+ [{ return Helper.matchOperandIsUndef(*${root}, 1); }]),
+ (apply [{ Helper.replaceInstWithConstant(*${root}, 0); }])>;
+
// Instructions where if any source operand is undef, the instruction can be
// replaced with undef.
def propagate_undef_any_op: GICombineRule<
@@ -955,6 +961,7 @@ def undef_combines : GICombineGroup<[undef_to_fp_zero, undef_to_int_zero,
undef_to_negative_one,
binop_left_undef_to_zero,
binop_right_undef_to_undef,
+ unary_undef_to_zero,
propagate_undef_any_op,
propagate_undef_all_ops,
propagate_undef_shuffle_mask,
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/combine-unary-undef-to-zero.mir b/llvm/test/CodeGen/AArch64/GlobalISel/combine-unary-undef-to-zero.mir
new file mode 100644
index 000000000000..1c5f5cbd17b3
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/combine-unary-undef-to-zero.mir
@@ -0,0 +1,41 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=aarch64-unknown-unknown -run-pass=aarch64-prelegalizer-combiner -verify-machineinstrs -o - %s | FileCheck %s
+
+# Test unary_op(undef) -> 0 combines
+
+...
+---
+name: abs_scalar
+tracksRegLiveness: true
+body: |
+ bb.0:
+ liveins: $w0
+ ; CHECK-LABEL: name: abs_scalar
+ ; CHECK: liveins: $w0
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: %abs:_(s32) = G_CONSTANT i32 0
+ ; CHECK-NEXT: $w0 = COPY %abs(s32)
+ ; CHECK-NEXT: RET_ReallyLR implicit $w0
+ %undef:_(s32) = G_IMPLICIT_DEF
+ %abs:_(s32) = G_ABS %undef
+ $w0 = COPY %abs(s32)
+ RET_ReallyLR implicit $w0
+...
+---
+name: abs_vector
+tracksRegLiveness: true
+body: |
+ bb.0:
+ liveins: $d0
+ ; CHECK-LABEL: name: abs_vector
+ ; CHECK: liveins: $d0
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+ ; CHECK-NEXT: %abs:_(<2 x s32>) = G_BUILD_VECTOR [[C]](s32), [[C]](s32)
+ ; CHECK-NEXT: $d0 = COPY %abs(<2 x s32>)
+ ; CHECK-NEXT: RET_ReallyLR implicit $d0
+ %undef:_(<2 x s32>) = G_IMPLICIT_DEF
+ %abs:_(<2 x s32>) = G_ABS %undef
+ $d0 = COPY %abs(<2 x s32>)
+ RET_ReallyLR implicit $d0
+...
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