Commit Graph

29 Commits

Author SHA1 Message Date
Hans Wennborg b64cb271dc SimplifyCFG: Omit range checks for switch lookup tables when default is unreachable
The range check would get optimized away later, but we might as well not emit
them in the first place.

http://reviews.llvm.org/D6471

llvm-svn: 227126
2015-01-26 19:52:34 +00:00
Hans Wennborg 6800008f04 SimplifyCFG: don't remove unreachable default switch destinations
An unreachable default destination can be exploited by other optimizations and
allows for more efficient lowering. Both the SDag switch lowering and
LowerSwitch can exploit unreachable defaults.

Also make TurnSwitchRangeICmp handle switches with unreachable default.
This is kind of separate change, but it cannot be tested without the change
above, and I don't want to land the change above without this since that would
regress other tests.

Differential Revision: http://reviews.llvm.org/D6471

llvm-svn: 227125
2015-01-26 19:52:32 +00:00
Hans Wennborg dcc6e5bc03 SimplifyCFG: check uses of constant-foldable instrs in switch destinations (PR20210)
The previous code assumed that such instructions could not have any uses
outside CaseDest, with the motivation that the instruction could not
dominate CommonDest because CommonDest has phi nodes in it. That simply
isn't true; e.g., CommonDest could have an edge back to itself.

llvm-svn: 225552
2015-01-09 22:13:31 +00:00
Hans Wennborg 5bef5b522b Revert r223049, r223050 and r223051 while investigating test failures.
I didn't foresee affecting the Clang test suite :/

llvm-svn: 223054
2014-12-01 17:36:43 +00:00
Hans Wennborg 269ebb612e SimplifyCFG: Omit range checks for switch lookup tables when default is unreachable
They would get optimized away later, but we might as well not emit them.

llvm-svn: 223051
2014-12-01 17:08:38 +00:00
Hans Wennborg 5a1e5c05d8 SimplifyCFG: don't remove unreachable default switch destinations
An unreachable default destination can be exploited by other optimizations, and
SDag lowering is now prepared to handle them efficiently.

For example, branches to the unreachable destination will be optimized away,
such as in the case of range checks for switch lookup tables.

On 64-bit Linux, this reduces the size of a clang bootstrap by 80 kB (and
Chromium by 30 kB).

llvm-svn: 223050
2014-12-01 17:08:35 +00:00
Erik Eckstein 0d86c7623f reinstate r222872: Peephole optimization in switch table lookup: reuse the guarding table comparison if possible.
Fixed missing dominance check.
Original commit message:

This optimization tries to reuse the generated compare instruction, if there is a comparison against the default value after the switch.
Example:
   if (idx < tablesize)
      r = table[idx]; // table does not contain default_value
   else
      r = default_value;
   if (r != default_value)
      ...
Is optimized to:
   cond = idx < tablesize;
   if (cond)
      r = table[idx];
   else
      r = default_value;
   if (cond)
      ...
Jump threading will then eliminate the second if(cond).

llvm-svn: 222891
2014-11-27 15:13:14 +00:00
Erik Eckstein 2190cd9ffa Revert "Peephole optimization in switch table lookup: reuse the guarding table comparison if possible."
It is breaking the clang bootstrag.

llvm-svn: 222877
2014-11-27 10:59:08 +00:00
Erik Eckstein e73e308ab9 Peephole optimization in switch table lookup: reuse the guarding table comparison if possible.
This optimization tries to reuse the generated compare instruction, if there is a comparison against the default value after the switch.
Example:
    if (idx < tablesize)
       r = table[idx]; // table does not contain default_value
    else
       r = default_value;
    if (r != default_value)
       ...
Is optimized to:
    cond = idx < tablesize;
    if (cond)
       r = table[idx];
    else
       r = default_value;
    if (cond)
       ...
\endcode
Jump threading will then eliminate the second if(cond).

llvm-svn: 222872
2014-11-27 08:33:51 +00:00
Hans Wennborg bda193edff Remove useless rdar:// comment from switch_to_lookup_table.ll test.
llvm-svn: 222772
2014-11-25 18:45:23 +00:00
Juergen Ributzka c9591e9bdb [SimplifyCFG] Make the value type of the hole check bitmask a power-of-2.
When converting a switch to a lookup table we might have to generate a bitmaks
to encode and check for holes in the original switch statement.

The type of this mask depends on the number of switch statements, which can
result in illegal types for pretty much all architectures.

To avoid unnecessary type legalization and help FastISel this commit increases
the size of the bitmask to next power-of-2 value when necessary.

This fixes rdar://problem/18984639.

llvm-svn: 222168
2014-11-17 19:39:56 +00:00
Erik Eckstein 105374fe5e Optimize switch lookup tables with linear mapping.
This is a simple optimization for switch table lookup:
It computes the output value directly with an (optional) mul and add if there is a linear mapping between index and output.
Example:

int f1(int x) {
  switch (x) {
    case 0: return 10;
    case 1: return 11;
    case 2: return 12;
    case 3: return 13;
  }
  return 0;
}

generates:

define i32 @f1(i32 %x) #0 {
entry:
  %0 = icmp ult i32 %x, 4
  br i1 %0, label %switch.lookup, label %return

switch.lookup:
  %switch.offset = add i32 %x, 10
  ret i32 %switch.offset

return:
  ret i32 0
}

llvm-svn: 222121
2014-11-17 09:13:57 +00:00
Marcello Maggioni 5bbe3df63f Switch to select optimization for two-case switches
This is the same optimization of r219233 with modifications to support PHIs with multiple incoming edges from the same block
and a test to check that this condition is handled.

llvm-svn: 219656
2014-10-14 01:58:26 +00:00
Joerg Sonnenberger 5ca10d0edb Revert r219223, it creates invalid PHI nodes.
llvm-svn: 219587
2014-10-12 17:16:04 +00:00
Marcello Maggioni 963bc87dbd Two case switch to select optimization
This optimization tries to convert switch instructions that are used to select a value with only 2 unique cases + default block
to a select or a couple of selects (depending if the default block is reachable or not).

The typical case this optimization wants to be able to optimize is this one:

Example:
switch (a) {
  case 10:                %0 = icmp eq i32 %a, 10
    return 10;            %1 = select i1 %0, i32 10, i32 4
  case 20:        ---->   %2 = icmp eq i32 %a, 20
    return 2;             %3 = select i1 %2, i32 2, i32 %1
  default:
    return 4;
}

It also sets the base for further optimizations that are planned and being reviewed.

llvm-svn: 219223
2014-10-07 18:16:44 +00:00
Manman Ren 062f58d550 [SimplifyCFG] fix accessing deleted PHINodes in switch-to-table conversion.
When we have a covered lookup table, make sure we don't delete PHINodes that
are cached in PHIs.

rdar://17887153

llvm-svn: 214642
2014-08-02 23:41:54 +00:00
Manman Ren 29a2005596 Try to fix the bots again by moving test to X86 directory.
llvm-svn: 213884
2014-07-24 17:57:09 +00:00
Hans Wennborg b03ebfb77e Don't build switch tables for dllimport and TLS variables in GEPs
This is a follow-up to r211331, which failed to notice that we were
returning early from ValidLookupTableConstant for GEPs.

llvm-svn: 211753
2014-06-26 00:30:52 +00:00
Hans Wennborg 4dc895164a Don't build switch lookup tables for dllimport or TLS variables
We would previously put dllimport variables in switch lookup tables, which
doesn't work because the address cannot be used in a constant initializer.
This is basically the same problem that we have in PR19955.

Putting TLS variables in switch tables also desn't work, because the
address of such a variable is not constant.

Differential Revision: http://reviews.llvm.org/D4220

llvm-svn: 211331
2014-06-20 00:38:12 +00:00
Alp Toker d3d017cf00 Reduce verbiage of lit.local.cfg files
We can just split targets_to_build in one place and make it immutable.

llvm-svn: 210496
2014-06-09 22:42:55 +00:00
Hans Wennborg b73c0b041d Allow switch-to-lookup table for tables with holes by adding bitmask check
This allows us to generate table lookups for code such as:

  unsigned test(unsigned x) {
    switch (x) {
      case 100: return 0;
      case 101: return 1;
      case 103: return 2;
      case 105: return 3;
      case 107: return 4;
      case 109: return 5;
      case 110: return 6;
      default: return f(x);
    }
  }

Since cases 102, 104, etc. are not constants, the lookup table has holes
in those positions. We therefore guard the table lookup with a bitmask check.

Patch by Jasper Neumann!

llvm-svn: 203694
2014-03-12 18:35:40 +00:00
Hans Wennborg 4744ac1733 Switch-to-lookup tables: set threshold to 3 cases
There has been an old FIXME to find the right cut-off for when it's worth
analyzing and potentially transforming a switch to a lookup table.

The switches always have two or more cases. I could not measure any speed-up
by transforming a switch with two cases. A switch with three cases gets a nice
speed-up, and I couldn't measure any compile-time regression, so I think this
is the right threshold.

In a Clang self-host, this causes 480 new switches to be transformed,
and reduces the final binary size with 8 KB.

llvm-svn: 199294
2014-01-15 05:00:27 +00:00
Hans Wennborg ac114a3ce7 Switch-to-lookup tables: Don't require a result for the default
case when the lookup table doesn't have any holes.

This means we can build a lookup table for switches like this:

  switch (x) {
    case 0: return 1;
    case 1: return 2;
    case 2: return 3;
    case 3: return 4;
    default: exit(1);
  }

The default case doesn't yield a constant result here, but that doesn't matter,
since a default result is only necessary for filling holes in the lookup table,
and this table doesn't have any holes.

This makes us transform 505 more switches in a clang bootstrap, and shaves 164 KB
off the resulting clang binary.

llvm-svn: 199025
2014-01-12 00:44:41 +00:00
Benjamin Kramer 7c30260ab3 SimplifyCFG: Use existing constant folding logic when forming switch tables.
Both simpler and more powerful than the hand-rolled folding logic.

llvm-svn: 194475
2013-11-12 12:24:36 +00:00
Daniel Dunbar 9efbedfd35 [tests] Cleanup initialization of test suffixes.
- Instead of setting the suffixes in a bunch of places, just set one master
   list in the top-level config. We now only modify the suffix list in a few
   suites that have one particular unique suffix (.ml, .mc, .yaml, .td, .py).

 - Aside from removing the need for a bunch of lit.local.cfg files, this enables
   4 tests that were inadvertently being skipped (one in
   Transforms/BranchFolding, a .s file each in DebugInfo/AArch64 and
   CodeGen/PowerPC, and one in CodeGen/SI which is now failing and has been
   XFAILED).

 - This commit also fixes a bunch of config files to use config.root instead of
   older copy-pasted code.

llvm-svn: 188513
2013-08-16 00:37:11 +00:00
Stephen Lin a76289aa1b Catch more CHECK that can be converted to CHECK-LABEL in Transforms for easier debugging. No functionality change.
This conversion was done with the following bash script:

  find test/Transforms -name "*.ll" | \
  while read NAME; do
    echo "$NAME"
    if ! grep -q "^; *RUN: *llc" $NAME; then
      TEMP=`mktemp -t temp`
      cp $NAME $TEMP
      sed -n "s/^define [^@]*@\([A-Za-z0-9_]*\)(.*$/\1/p" < $NAME | \
      while read FUNC; do
        sed -i '' "s/;\(.*\)\([A-Za-z0-9_]*\):\( *\)define\([^@]*\)@$FUNC\([( ]*\)\$/;\1\2-LABEL:\3define\4@$FUNC(/g" $TEMP
      done
      mv $TEMP $NAME
    fi
  done

llvm-svn: 186269
2013-07-14 01:50:49 +00:00
Stephen Lin c1c7a1309c Update Transforms tests to use CHECK-LABEL for easier debugging. No functionality change.
This update was done with the following bash script:

  find test/Transforms -name "*.ll" | \
  while read NAME; do
    echo "$NAME"
    if ! grep -q "^; *RUN: *llc" $NAME; then
      TEMP=`mktemp -t temp`
      cp $NAME $TEMP
      sed -n "s/^define [^@]*@\([A-Za-z0-9_]*\)(.*$/\1/p" < $NAME | \
      while read FUNC; do
        sed -i '' "s/;\(.*\)\([A-Za-z0-9_]*\):\( *\)@$FUNC\([( ]*\)\$/;\1\2-LABEL:\3@$FUNC(/g" $TEMP
      done
      mv $TEMP $NAME
    fi
  done

llvm-svn: 186268
2013-07-14 01:42:54 +00:00
Evan Cheng 65df808f62 Fix logic to determine whether to turn a switch into a lookup table. When
the tables cannot fit in registers (i.e. bitmap), do not emit the table
if it's using an illegal type.

rdar://12779436

llvm-svn: 168970
2012-11-30 02:02:42 +00:00
Hans Wennborg c3c8d95c51 Only do switch-to-lookup table transformation when TargetTransformInfo
is available.

llvm-svn: 167552
2012-11-07 21:35:12 +00:00