llvm-mirror/test/MachineVerifier/generic-vreg-undef-use.mir
Matt Arsenault 58a9482211 GlobalISel: Disallow undef generic virtual register uses
With an undef operand, it's possible for getVRegDef to fail and return
null. This is an edge case very little code bothered to
consider. Proper gMIR should use G_IMPLICIT_DEF instead.

I initially tried to apply this restriction to all SSA MIR, so then
getVRegDef would never fail anywhere. However, ProcessImplicitDefs
does technically run while the function is in SSA. ProcessImplicitDefs
and DetectDeadLanes would need to either move, or a new pseudo-SSA
type of function property would need to be introduced.
2020-06-30 19:18:01 -04:00

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# RUN: not --crash llc -march=aarch64 -o /dev/null -run-pass=none -verify-machineinstrs %s 2>&1 | FileCheck %s
# REQUIRES: aarch64-registered-target
# Undef uses are illegal for generic vregs.
---
name: test_undef_use
liveins:
body: |
bb.0:
%0:_(s32) = G_CONSTANT i32 0
; Test generic instruction
; CHECK: *** Bad machine code: Generic virtual register use cannot be undef ***
G_STORE %0, undef %1:_(p0) :: (store 4)
; Make sure this fails on a post-isel generic instruction.
; CHECK: *** Bad machine code: Generic virtual register use cannot be undef ***
$x0 = COPY undef %2:_(s64)
; Make sure this fails with a target instruction
; CHECK: *** Bad machine code: Generic virtual register use cannot be undef ***
RET_ReallyLR implicit $x0, implicit undef %3:_(s32)
...