Index: llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
===================================================================
--- llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
+++ llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
@@ -211,6 +211,17 @@
/// Return true if a G_STORE instruction \p MI is storing an undef value.
bool matchUndefStore(MachineInstr &MI);
+ /// Return true if a G_SELECT instruction \p MI has an undef comparison.
+ bool matchUndefSelectCmp(MachineInstr &MI);
+
+ /// Return true if a G_SELECT instruction \p MI has an undef select value. If
+ /// true, \p OpIdx will store the operand index of the known selected value.
+ bool matchUndefSelectVals(MachineInstr &MI, unsigned &ValIdx);
+
+ /// Return true if a G_SELECT instruction \p MI has a constant comparison. If
+ /// true, \p OpIdx will store the operand index of the known selected value.
+ bool matchConstantSelectCmp(MachineInstr &MI, unsigned &OpIdx);
+
/// Replace an instruction with a G_FCONSTANT with value \p C.
bool replaceInstWithFConstant(MachineInstr &MI, double C);
Index: llvm/include/llvm/Target/GlobalISel/Combine.td
===================================================================
--- llvm/include/llvm/Target/GlobalISel/Combine.td
+++ llvm/include/llvm/Target/GlobalISel/Combine.td
@@ -203,6 +203,35 @@
(apply [{ return Helper.replaceSingleDefInstWithOperand(*${root}, 2); }])
>;
+// Fold (undef ? x : y) -> x
+def select_undef_cmp: GICombineRule<
+ (defs root:$root),
+ (match (wip_match_opcode G_SELECT):$root,
+ [{ return Helper.matchUndefSelectCmp(*${root}); }]),
+ (apply [{ return Helper.replaceSingleDefInstWithOperand(*${root}, 2); }])
+>;
+
+// Fold (cmp ? x : undef) -> x
+// Fold (cmp ? undef : y) -> y
+// Fold (cmp ? undef : undef) -> undef
+def select_undef_val_matchdata : GIDefMatchData<"unsigned">;
+def select_undef_val: GICombineRule<
+ (defs root:$root, select_undef_val_matchdata:$matchinfo),
+ (match (wip_match_opcode G_SELECT):$root,
+ [{ return Helper.matchUndefSelectVals(*${root}, ${matchinfo}); }]),
+ (apply [{ return Helper.replaceSingleDefInstWithOperand(*${root}, ${matchinfo}); }])
+>;
+
+// Fold (true ? x : y) -> x
+// Fold (false ? x : y) -> y
+def select_constant_cmp_matchdata : GIDefMatchData<"unsigned">;
+def select_constant_cmp: GICombineRule<
+ (defs root:$root, select_constant_cmp_matchdata:$matchinfo),
+ (match (wip_match_opcode G_SELECT):$root,
+ [{ return Helper.matchConstantSelectCmp(*${root}, ${matchinfo}); }]),
+ (apply [{ return Helper.replaceSingleDefInstWithOperand(*${root}, ${matchinfo}); }])
+>;
+
// Fold x op 0 -> x
def right_identity_zero: GICombineRule<
(defs root:$root),
@@ -263,7 +292,10 @@
binop_same_val, binop_left_to_zero,
binop_right_to_zero]>;
+def select_combines : GICombineGroup<[select_undef_cmp, select_undef_val,
+ select_constant_cmp]>;
+
def trivial_combines : GICombineGroup<[copy_prop, mul_to_shl]>;
def all_combines : GICombineGroup<[trivial_combines, ptr_add_immed_chain,
combines_for_extload, combine_indexed_load_store, undef_combines,
- identity_combines, simplify_add_to_sub]>;
+ identity_combines, select_combines, simplify_add_to_sub]>;
Index: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
===================================================================
--- llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -1537,6 +1537,39 @@
MRI);
}
+bool CombinerHelper::matchUndefSelectCmp(MachineInstr &MI) {
+ assert(MI.getOpcode() == TargetOpcode::G_SELECT);
+ return getOpcodeDef(TargetOpcode::G_IMPLICIT_DEF, MI.getOperand(1).getReg(),
+ MRI);
+}
+
+bool CombinerHelper::matchUndefSelectVals(MachineInstr &MI, unsigned &OpIdx) {
+ assert(MI.getOpcode() == TargetOpcode::G_SELECT);
+ if (getOpcodeDef(TargetOpcode::G_IMPLICIT_DEF, MI.getOperand(2).getReg(),
+ MRI)) {
+ // Select val0 is undef, choose select val1.
+ OpIdx = 3;
+ return true;
+ }
+ if (getOpcodeDef(TargetOpcode::G_IMPLICIT_DEF, MI.getOperand(3).getReg(),
+ MRI)) {
+ // Select val1 is undef, choose select val0.
+ OpIdx = 2;
+ return true;
+ }
+ return false;
+}
+
+bool CombinerHelper::matchConstantSelectCmp(MachineInstr &MI, unsigned &OpIdx) {
+ assert(MI.getOpcode() == TargetOpcode::G_SELECT);
+ if (auto MaybeCstCmp =
+ getConstantVRegValWithLookThrough(MI.getOperand(1).getReg(), MRI)) {
+ OpIdx = MaybeCstCmp->Value ? 2 : 3;
+ return true;
+ }
+ return false;
+}
+
bool CombinerHelper::eraseInst(MachineInstr &MI) {
MI.eraseFromParent();
return true;
Index: llvm/test/CodeGen/AArch64/GlobalISel/combine-select.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AArch64/GlobalISel/combine-select.mir
@@ -0,0 +1,108 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -run-pass=aarch64-prelegalizer-combiner -verify-machineinstrs -mtriple aarch64-unknown-unknown %s -o - | FileCheck %s
+# RUN: llc -debugify-and-strip-all-safe -run-pass=aarch64-prelegalizer-combiner -verify-machineinstrs -mtriple aarch64-unknown-unknown %s -o - | FileCheck %s
+---
+# select (c, x, x) -> x
+name: test_combine_select_same_res
+body: |
+ bb.1:
+ liveins: $x0, $x1
+ ; CHECK-LABEL: name: test_combine_select_same_res
+ ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+ ; CHECK: $x0 = COPY [[COPY]](s64)
+ %0:_(s64) = COPY $x0
+ %1:_(s1) = G_TRUNC %0
+ %2:_(s64) = G_SELECT %1, %0, %0
+ $x0 = COPY %2(s64)
+...
+---
+# select (undef, x, y) -> x
+name: test_combine_select_undef_res0_res1
+body: |
+ bb.1:
+ liveins: $x0, $x1
+ ; CHECK-LABEL: name: test_combine_select_undef_res0_res1
+ ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+ ; CHECK: $x0 = COPY [[COPY]](s64)
+ %0:_(s64) = COPY $x0
+ %1:_(s64) = COPY $x1
+ %2:_(s1) = G_IMPLICIT_DEF
+ %3:_(s64) = G_SELECT %2, %0, %1
+ $x0 = COPY %3(s64)
+...
+---
+# select (c, undef, y) -> y
+name: test_combine_select_cmp_undef_res1
+body: |
+ bb.1:
+ liveins: $x0
+ ; CHECK-LABEL: name: test_combine_select_cmp_undef_res1
+ ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+ ; CHECK: $x0 = COPY [[COPY]](s64)
+ %0:_(s64) = COPY $x0
+ %1:_(s1) = G_TRUNC %0
+ %2:_(s64) = G_IMPLICIT_DEF
+ %3:_(s64) = G_SELECT %1, %2, %0
+ $x0 = COPY %3(s64)
+...
+---
+# select (c, x, undef) -> x
+name: test_combine_select_cmp_res0_undef
+body: |
+ bb.1:
+ liveins: $x0
+ ; CHECK-LABEL: name: test_combine_select_cmp_res0_undef
+ ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+ ; CHECK: $x0 = COPY [[COPY]](s64)
+ %0:_(s64) = COPY $x0
+ %1:_(s1) = G_TRUNC %0
+ %2:_(s64) = G_IMPLICIT_DEF
+ %3:_(s64) = G_SELECT %1, %0, %2
+ $x0 = COPY %3(s64)
+...
+---
+# select (c, undef, undef) -> undef
+name: test_combine_select_cmp_undef_undef
+body: |
+ bb.1:
+ liveins: $x0
+ ; CHECK-LABEL: name: test_combine_select_cmp_undef_undef
+ ; CHECK: [[DEF:%[0-9]+]]:_(s64) = G_IMPLICIT_DEF
+ ; CHECK: $x0 = COPY [[DEF]](s64)
+ %0:_(s64) = COPY $x0
+ %1:_(s1) = G_TRUNC %0
+ %2:_(s64) = G_IMPLICIT_DEF
+ %3:_(s64) = G_IMPLICIT_DEF
+ %4:_(s64) = G_SELECT %1, %2, %3
+ $x0 = COPY %3(s64)
+...
+---
+# select (false, x, y) -> y
+name: test_combine_select_false_res0_res1
+body: |
+ bb.1:
+ liveins: $x0, $x1
+ ; CHECK-LABEL: name: test_combine_select_false_res0_res1
+ ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x1
+ ; CHECK: $x0 = COPY [[COPY]](s64)
+ %0:_(s64) = COPY $x0
+ %1:_(s64) = COPY $x1
+ %2:_(s1) = G_CONSTANT i1 false
+ %3:_(s64) = G_SELECT %2, %0, %1
+ $x0 = COPY %3(s64)
+...
+---
+# select (true, x, y) -> x
+name: test_combine_select_true_res0_res1
+body: |
+ bb.1:
+ liveins: $x0, $x1
+ ; CHECK-LABEL: name: test_combine_select_true_res0_res1
+ ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+ ; CHECK: $x0 = COPY [[COPY]](s64)
+ %0:_(s64) = COPY $x0
+ %1:_(s64) = COPY $x1
+ %2:_(s1) = G_CONSTANT i1 true
+ %3:_(s64) = G_SELECT %2, %0, %1
+ $x0 = COPY %3(s64)
+...