[UpdateTestChecks] Don't skip first line with --filter

[sebastian-ne]

Summary

body_start was never used, resulting in the first filtered line to be
skipped.
Fixes the --filter option introduced in D117694.

[sebastian-ne]

friendly ping for review

[spatel]

LGTM - I haven't used this option with the script, but the test diffs look right.

llvm/test/tools/UpdateTestChecks/update_llc_test_checks/Inputs/x86-non-temporal.ll.filter-out.expected

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --filter-out "movnt"
 ; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mattr=+avx2 | FileCheck %s
 
 define i32 @f(<8 x float> %A, i8* %B, <4 x double> %C, <4 x i64> %E, <8 x i32> %F, <16 x i16> %G, <32 x i8> %H, i32* %loadptr) nounwind {
 ; CHECK-LABEL: f:
+; CHECK:  # %bb.0:
 ; CHECK:    movl (%rsi), %eax
 ; CHECK:    vaddps {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm0, %ymm0
 ; CHECK:    vpaddq {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm2, %ymm0
 ; CHECK:    addl (%rsi), %eax
 ; CHECK:    vaddpd {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm1, %ymm0
 ; CHECK:    addl (%rsi), %eax
 ; CHECK:    vpaddd {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm3, %ymm0
 ; CHECK:    addl (%rsi), %eax

llvm/test/tools/UpdateTestChecks/update_llc_test_checks/Inputs/x86-non-temporal.ll.filter.expected

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --filter "movnt"
 ; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mattr=+avx2 | FileCheck %s
 
 define i32 @f(<8 x float> %A, i8* %B, <4 x double> %C, <4 x i64> %E, <8 x i32> %F, <16 x i16> %G, <32 x i8> %H, i32* %loadptr) nounwind {
 ; CHECK-LABEL: f:
+; CHECK:    vmovntps %ymm0, (%rdi)
 ; CHECK:    vmovntdq %ymm0, (%rdi)
 ; CHECK:    vmovntpd %ymm0, (%rdi)
 ; CHECK:    vmovntdq %ymm0, (%rdi)
 ; CHECK:    vmovntdq %ymm0, (%rdi)
 ; CHECK:    vmovntdq %ymm0, (%rdi)
   %v0 = load i32, i32* %loadptr, align 1
   %cast = bitcast i8* %B to <8 x float>*
   %A2 = fadd <8 x float> %A, <float 1.0, float 2.0, float 3.0, float 4.0, float 5.0, float 6.0, float 7.0, float 8.0>

llvm/test/tools/UpdateTestChecks/update_llc_test_checks/Inputs/x86-non-temporal.ll.multifilter.expected

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --filter "LCPI[0-9]+_[0-9]+" --filter "movnt" --filter "(%esp|%rsi)"
 ; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mattr=+avx2 | FileCheck %s
 
 define i32 @f(<8 x float> %A, i8* %B, <4 x double> %C, <4 x i64> %E, <8 x i32> %F, <16 x i16> %G, <32 x i8> %H, i32* %loadptr) nounwind {
 ; CHECK-LABEL: f:
+; CHECK:    movl (%rsi), %eax
 ; CHECK:    vaddps {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm0, %ymm0
 ; CHECK:    vmovntps %ymm0, (%rdi)
 ; CHECK:    vpaddq {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm2, %ymm0
 ; CHECK:    addl (%rsi), %eax
 ; CHECK:    vmovntdq %ymm0, (%rdi)
 ; CHECK:    vaddpd {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm1, %ymm0
 ; CHECK:    addl (%rsi), %eax
 ; CHECK:    vmovntpd %ymm0, (%rdi)

llvm/utils/UpdateTestChecks/common.py

for checkprefix in checkprefixes:
       if is_backend:
         body_start = 1
         if is_filtered:
           # For filtered output we don't add "-NEXT" so don't add extra spaces
           # before the first line.
           body_start = 0
         else:
           output_lines.append('%s %s:       %s' % (comment_marker, checkprefix, func_body[0]))
-        for func_line in func_body[1:]:
+        for func_line in func_body[body_start:]:
           if func_line.strip() == '':
             output_lines.append('%s %s-EMPTY:' % (comment_marker, checkprefix))
           else:
             check_suffix = '-NEXT' if not is_filtered else ''
             output_lines.append('%s %s%s:  %s' % (comment_marker, checkprefix,
                                                   check_suffix, func_line))
         break