[llvm] r354018 - [ARM] Ensure we update the correct flags in the peephole optimiser
David Green via llvm-commits
llvm-commits at lists.llvm.org
Thu Feb 14 03:09:24 PST 2019
Author: dmgreen
Date: Thu Feb 14 03:09:24 2019
New Revision: 354018
URL: http://llvm.org/viewvc/llvm-project?rev=354018&view=rev
Log:
[ARM] Ensure we update the correct flags in the peephole optimiser
The Arm peephole optimiser code keeps track of both an MI and a SubAdd that can
be used to optimise away a CMP. In the rare case that both are found and not
ruled-out as valid, we could end up setting the flags on the wrong one.
Instead make sure we are using SubAdd if it exists, as it will be closer to the
CMP.
The testcase here is a little theoretical, with a dead def of cpsr. It should
hopefully show the point.
Differential Revision: https://reviews.llvm.org/D58176
Added:
llvm/trunk/test/CodeGen/Thumb2/peephole-addsub.mir
Modified:
llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
Modified: llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp?rev=354018&r1=354017&r2=354018&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp Thu Feb 14 03:09:24 2019
@@ -2825,8 +2825,11 @@ bool ARMBaseInstrInfo::optimizeCompareIn
if (!MI && !SubAdd)
return false;
- // The single candidate is called MI.
- if (!MI) MI = SubAdd;
+ // If we found a SubAdd, use it as it will be closer to the CMP
+ if (SubAdd) {
+ MI = SubAdd;
+ IsThumb1 = false;
+ }
// We can't use a predicated instruction - it doesn't always write the flags.
if (isPredicated(*MI))
Added: llvm/trunk/test/CodeGen/Thumb2/peephole-addsub.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/Thumb2/peephole-addsub.mir?rev=354018&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/Thumb2/peephole-addsub.mir (added)
+++ llvm/trunk/test/CodeGen/Thumb2/peephole-addsub.mir Thu Feb 14 03:09:24 2019
@@ -0,0 +1,35 @@
+# RUN: llc -run-pass=peephole-opt -verify-machineinstrs -o - %s | FileCheck %s
+--- |
+ target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+ target triple = "thumbv7-none-eabi"
+
+ define i32 @test(i32 %a, i32 %b) {
+ unreachable
+ }
+
+...
+---
+name: test
+tracksRegLiveness: true
+liveins:
+ - { reg: '$r0', virtual-reg: '%0' }
+ - { reg: '$r1', virtual-reg: '%1' }
+body: |
+ bb.0 (%ir-block.0):
+ liveins: $r0, $r1
+
+ %1:rgpr = COPY $r1
+ %0:rgpr = COPY $r0
+ %2:rgpr = t2MOVi 1, 14, $noreg, $noreg
+ %3:gprnopc = t2ADDrr %0, %1, 14, $noreg, $noreg
+ %4:gprnopc = t2SUBri %3, 0, 14, $noreg, def dead $cpsr
+ t2CMPri killed %3, 0, 14, $noreg, implicit-def $cpsr
+ %5:rgpr = t2MOVCCi %2, 0, 7, $cpsr
+ $r0 = COPY %5
+ tBX_RET 14, $noreg, implicit $r0
+
+# CHECK-LABEL: name: test
+# CHECK: %3:gprnopc = t2ADDrr %0, %1, 14, $noreg, $noreg
+# CHECK-NEXT: %4:gprnopc = t2SUBri %3, 0, 14, $noreg, def $cpsr
+# CHECK-NEXT: %5:rgpr = t2MOVCCi %2, 0, 7, $cpsr
+...
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