[PowerPC, test] Fix use of undef FileCheck var

[thopre]

Summary

LLVM test CodeGen/PowerPC/ppc-disable-non-volatile-cr.ll tries to check
for the absence of a sequence of instructions with several CHECK-NOT
with one of those directives using a variable defined in another.
However CHECK-NOT are checked independently so that is using a variable
defined in a pattern that should not occur in the input.

This commit changes occurence of the variable for the regex used in its
definition, thereby making each CHECK-NOT independent.

[NeHuang]

LGTM. Thanks! Please give it another 24 hours before commit to wait for the other reviewers' comment.

[nemanjai]

LGTM. Thanks for fixing this.

llvm/test/CodeGen/PowerPC/ppc-disable-non-volatile-cr.ll

 ; Note: Test option to disable use of non-volatile CR to avoid CR spilling in prologue.
 ; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux-gnu -ppc-disable-non-volatile-cr\
 ; RUN:     -ppc-asm-full-reg-names -ppc-vsr-nums-as-vr < %s | FileCheck --check-prefix=CHECK-DISABLE %s
 ; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux-gnu\
 ; RUN:     -ppc-asm-full-reg-names -ppc-vsr-nums-as-vr < %s | FileCheck --check-prefix=CHECK-ENABLE %s
 
 ; Function Attrs: nounwind
 define dso_local signext i32 @DisableNonVolatileCR(i32 signext %a, i32 signext %b) {
 ; CHECK-DISABLE-LABEL: DisableNonVolatileCR:
 ; CHECK-DISABLE:       # %bb.0: # %entry
-; CHECK-DISABLE-NOT:    mfocrf [[REG1:r[0-9]+]]
-; CHECK-DISABLE-NOT:    stw [[REG1]]
+; CHECK-DISABLE-NOT:    mfocrf {{r[0-9]+}}
+; CHECK-DISABLE-NOT:    stw {{r[0-9]+}}
 ; CHECK-DISABLE:        stdu r1
 ; CHECK-DISABLE-DAG:    mfocrf [[REG2:r[0-9]+]]
 ; CHECK-DISABLE-DAG:    stw [[REG2]]
 ; CHECK-DISABLE:        # %bb.1: # %if.then
 ;
 ; CHECK-ENABLE-LABEL: DisableNonVolatileCR:
 ; CHECK-ENABLE:       # %bb.0: # %entry
 ; CHECK-ENABLE-DAG:    mfocrf [[REG1:r[0-9]+]]
 ; CHECK-ENABLE-DAG:    stw [[REG1]]
 ; CHECK-ENABLE:        stdu r1
-; CHECK-ENABLE-NOT:    mfocrf [[REG2:r[0-9]+]]
-; CHECK-ENABLE-NOT:    stw [[REG2]]
+; CHECK-ENABLE-NOT:    mfocrf {{r[0-9]+}}
+; CHECK-ENABLE-NOT:    stw {{r[0-9]+}}
 ; CHECK-ENABLE:        # %bb.1: # %if.then
 
 entry:
   %cmp = icmp slt i32 %a, %b
   br i1 %cmp, label %if.then, label %if.else
 
 if.then:                                          ; preds = %entry
   tail call void bitcast (void (...)* @fa to void ()*)()