[llvm] r223050 - SimplifyCFG: don't remove unreachable default switch destinations
Hans Wennborg
hans at hanshq.net
Mon Dec 1 09:08:35 PST 2014
Author: hans
Date: Mon Dec 1 11:08:35 2014
New Revision: 223050
URL: http://llvm.org/viewvc/llvm-project?rev=223050&view=rev
Log:
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).
Modified:
llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
llvm/trunk/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=223050&r1=223049&r2=223050&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Mon Dec 1 11:08:35 2014
@@ -3120,55 +3120,6 @@ bool SimplifyCFGOpt::SimplifyUnreachable
--i; --e;
Changed = true;
}
- // If the default value is unreachable, figure out the most popular
- // destination and make it the default.
- if (SI->getDefaultDest() == BB) {
- std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
- for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
- i != e; ++i) {
- std::pair<unsigned, unsigned> &entry =
- Popularity[i.getCaseSuccessor()];
- if (entry.first == 0) {
- entry.first = 1;
- entry.second = i.getCaseIndex();
- } else {
- entry.first++;
- }
- }
-
- // Find the most popular block.
- unsigned MaxPop = 0;
- unsigned MaxIndex = 0;
- BasicBlock *MaxBlock = nullptr;
- for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
- I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
- if (I->second.first > MaxPop ||
- (I->second.first == MaxPop && MaxIndex > I->second.second)) {
- MaxPop = I->second.first;
- MaxIndex = I->second.second;
- MaxBlock = I->first;
- }
- }
- if (MaxBlock) {
- // Make this the new default, allowing us to delete any explicit
- // edges to it.
- SI->setDefaultDest(MaxBlock);
- Changed = true;
-
- // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
- // it.
- if (isa<PHINode>(MaxBlock->begin()))
- for (unsigned i = 0; i != MaxPop-1; ++i)
- MaxBlock->removePredecessor(SI->getParent());
-
- for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
- i != e; ++i)
- if (i.getCaseSuccessor() == MaxBlock) {
- SI->removeCase(i);
- --i; --e;
- }
- }
- }
} else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
if (II->getUnwindDest() == BB) {
// Convert the invoke to a call instruction. This would be a good
Modified: llvm/trunk/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/UnreachableEliminate.ll?rev=223050&r1=223049&r2=223050&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/UnreachableEliminate.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/UnreachableEliminate.ll Mon Dec 1 11:08:35 2014
@@ -46,32 +46,6 @@ T:
ret i32 2
}
-; PR9450
-define i32 @test4(i32 %v, i32 %w) {
-; CHECK: entry:
-; CHECK-NEXT: switch i32 %v, label %T [
-; CHECK-NEXT: i32 3, label %V
-; CHECK-NEXT: i32 2, label %U
-; CHECK-NEXT: ]
-
-entry:
- br label %SWITCH
-V:
- ret i32 7
-SWITCH:
- switch i32 %v, label %default [
- i32 1, label %T
- i32 2, label %U
- i32 3, label %V
- ]
-default:
- unreachable
-U:
- ret i32 %w
-T:
- ret i32 2
-}
-
;; We can either convert the following control-flow to a select or remove the
;; unreachable control flow because of the undef store of null. Make sure we do
Modified: llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll?rev=223050&r1=223049&r2=223050&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll Mon Dec 1 11:08:35 2014
@@ -21,8 +21,8 @@ target triple = "x86_64-unknown-linux-gn
; The table for @cprop
; CHECK: @switch.table5 = private unnamed_addr constant [7 x i32] [i32 5, i32 42, i32 126, i32 -452, i32 128, i32 6, i32 7]
-; The table for @unreachable
-; CHECK: @switch.table6 = private unnamed_addr constant [5 x i32] [i32 0, i32 0, i32 0, i32 1, i32 -1]
+; The table for @unreachable_case
+; CHECK: @switch.table6 = private unnamed_addr constant [9 x i32] [i32 0, i32 0, i32 0, i32 2, i32 -1, i32 1, i32 1, i32 1, i32 1]
; A simple int-to-int selection switch.
; It is dense enough to be replaced by table lookup.
@@ -752,7 +752,7 @@ return:
; CHECK: %switch.gep = getelementptr inbounds [7 x i32]* @switch.table5, i32 0, i32 %switch.tableidx
}
-define i32 @unreachable(i32 %x) {
+define i32 @unreachable_case(i32 %x) {
entry:
switch i32 %x, label %sw.default [
i32 0, label %sw.bb
@@ -770,15 +770,15 @@ sw.bb: br label %return
sw.bb1: unreachable
sw.bb2: br label %return
sw.bb3: br label %return
-sw.default: unreachable
+sw.default: br label %return
return:
- %retval.0 = phi i32 [ 1, %sw.bb3 ], [ -1, %sw.bb2 ], [ 0, %sw.bb ]
+ %retval.0 = phi i32 [ 1, %sw.bb3 ], [ -1, %sw.bb2 ], [ 0, %sw.bb ], [ 2, %sw.default ]
ret i32 %retval.0
-; CHECK-LABEL: @unreachable(
+; CHECK-LABEL: @unreachable_case(
; CHECK: switch.lookup:
-; CHECK: getelementptr inbounds [5 x i32]* @switch.table6, i32 0, i32 %switch.tableidx
+; CHECK: getelementptr inbounds [9 x i32]* @switch.table6, i32 0, i32 %switch.tableidx
}
; Don't create a table with illegal type
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