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middle-end/9707: Unnecessary range test in switches with less than 4 cases

From: gertom at rgai dot hu
To: gcc-gnats at gcc dot gnu dot org
Date: 14 Feb 2003 16:43:15 -0000
Subject: middle-end/9707: Unnecessary range test in switches with less than 4 cases
Reply-to: gertom at rgai dot hu

>Number:         9707
>Category:       middle-end
>Synopsis:       Unnecessary range test in switches with less than 4 cases
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          pessimizes-code
>Submitter-Id:   net
>Arrival-Date:   Fri Feb 14 16:46:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     Tamás Gergely
>Release:        gcc version 3.3 20030210 (prerelease)
>Organization:
>Environment:
BUILD & HOST: Linux 2.4.20 i686 unknown
TARGET: arm-unknown-elf
>Description:
When a switch has less than 4 cases gcc tests for the middle-case-value and makes an additional less-greater check instead of immediately evaluating the other case-values. If there are more case branches in the switch, this kind of checking would speed up the search of the corresponding case branch (but those switches are solved with jump-tables anyway). But for only a few case branches, the direct equality checks would be better.
>How-To-Repeat:
arm-elf-gcc -S -g0 -Os -o 01_3d.s ./01_3d.i

//01_3d.i

# 1 "01_3d.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "01_3d.c"
unsigned int g;
int main ()
{
  int r;
  switch (r) {
    case 1:
             g=11;
        break;
    case 2:
             g=12;
        break;
    case 3:
             g=13;
        break;
    default:
             g=20;
        break;
  }
  return 0;
}
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
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