[llvm] b9bf930 - [AArch64][GlobalISel] Walk through G_TRUNC in getTestBitReg
Jessica Paquette via llvm-commits
llvm-commits at lists.llvm.org
Fri Jan 31 11:11:19 PST 2020
Author: Jessica Paquette
Date: 2020-01-31T11:09:55-08:00
New Revision: b9bf9305d108d9f9d017d84dc38f4d0a88c5d505
URL: https://github.com/llvm/llvm-project/commit/b9bf9305d108d9f9d017d84dc38f4d0a88c5d505
DIFF: https://github.com/llvm/llvm-project/commit/b9bf9305d108d9f9d017d84dc38f4d0a88c5d505.diff
LOG: [AArch64][GlobalISel] Walk through G_TRUNC in getTestBitReg
When you encounter a G_TRUNC, you are moving from a larger type to a smaller
type.
Asking for the i-th bit on a larger value is the same as asking for the i-th
bit on a smaller value.
So, we should always be able to walk through G_TRUNC when computing the bit
for a TB(N)Z.
Differential Revision: https://reviews.llvm.org/D73748
Added:
llvm/test/CodeGen/AArch64/GlobalISel/opt-fold-trunc-tbz-tbnz.mir
Modified:
llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
index b398da90128e..790ea72dff4d 100644
--- a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
@@ -998,7 +998,11 @@ static Register getTestBitReg(Register Reg, MachineRegisterInfo &MRI) {
Register NextReg;
// (tbz (any_ext x), b) -> (tbz x, b) if we don't use the extended bits.
- if (Opc == TargetOpcode::G_ANYEXT || Opc == TargetOpcode::G_ZEXT)
+ //
+ // (tbz (trunc x), b) -> (tbz x, b) is always safe, because the bit number
+ // on the truncated x is the same as the bit number on x.
+ if (Opc == TargetOpcode::G_ANYEXT || Opc == TargetOpcode::G_ZEXT ||
+ Opc == TargetOpcode::G_TRUNC)
NextReg = MI->getOperand(1).getReg();
// Did we find something worth folding?
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/opt-fold-trunc-tbz-tbnz.mir b/llvm/test/CodeGen/AArch64/GlobalISel/opt-fold-trunc-tbz-tbnz.mir
new file mode 100644
index 000000000000..a2b03e146ce8
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/opt-fold-trunc-tbz-tbnz.mir
@@ -0,0 +1,35 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple aarch64-unknown-unknown -run-pass=instruction-select -verify-machineinstrs %s -o - | FileCheck %s
+...
+---
+name: fold_trunc
+alignment: 4
+legalized: true
+regBankSelected: true
+tracksRegLiveness: true
+body: |
+ ; CHECK-LABEL: name: fold_trunc
+ ; CHECK: bb.0:
+ ; CHECK: successors: %bb.0(0x40000000), %bb.1(0x40000000)
+ ; CHECK: liveins: $x0
+ ; CHECK: %copy:gpr64all = COPY $x0
+ ; CHECK: [[COPY:%[0-9]+]]:gpr32all = COPY %copy.sub_32
+ ; CHECK: [[COPY1:%[0-9]+]]:gpr32 = COPY [[COPY]]
+ ; CHECK: TBNZW [[COPY1]], 3, %bb.1
+ ; CHECK: B %bb.0
+ ; CHECK: bb.1:
+ ; CHECK: RET_ReallyLR
+ bb.0:
+ successors: %bb.0, %bb.1
+ liveins: $x0
+ %copy:gpr(s64) = COPY $x0
+ %bit:gpr(s32) = G_CONSTANT i32 8
+ %zero:gpr(s32) = G_CONSTANT i32 0
+ %fold_me:gpr(s32) = G_TRUNC %copy(s64)
+ %and:gpr(s32) = G_AND %fold_me, %bit
+ %cmp:gpr(s32) = G_ICMP intpred(ne), %and(s32), %zero
+ %cmp_trunc:gpr(s1) = G_TRUNC %cmp(s32)
+ G_BRCOND %cmp_trunc(s1), %bb.1
+ G_BR %bb.0
+ bb.1:
+ RET_ReallyLR
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