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During the CodeGenPrepare we often lower intrinsics (such as objsize) 

and allow some optimizations to turn conditional branches into unconditional.
This commit adds a simple control-flow optimization which merges two consecutive
basic blocks which are connected by a single edge. This allows the codegen to
operate on larger basic blocks.

rdar://11973998

llvm-svn: 161852
This commit is contained in:
Nadav Rotem 2012-08-14 05:19:07 +00:00
parent 160522c25a
commit 70409991bc
8 changed files with 62 additions and 22 deletions
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39
llvm/lib/Transforms/Scalar/CodeGenPrepare.cpp
View File

@ -116,6 +116,7 @@ namespace {
}
private:
bool EliminateFallThrough(Function &F);
bool EliminateMostlyEmptyBlocks(Function &F);
bool CanMergeBlocks(const BasicBlock *BB, const BasicBlock *DestBB) const;
void EliminateMostlyEmptyBlock(BasicBlock *BB);
@ -192,6 +193,11 @@ bool CodeGenPrepare::runOnFunction(Function &F) {
I = WorkList.begin(), E = WorkList.end(); I != E; ++I)
DeleteDeadBlock(*I);
// Merge pairs of basic blocks with unconditional branches, connected by
// a single edge.
if (EverMadeChange || MadeChange)
MadeChange |= EliminateFallThrough(F);
if (MadeChange)
ModifiedDT = true;
EverMadeChange |= MadeChange;
@ -203,6 +209,39 @@ bool CodeGenPrepare::runOnFunction(Function &F) {
return EverMadeChange;
}
/// EliminateFallThrough - Merge basic blocks which are connected
/// by a single edge, where one of the basic blocks has a single successor
/// pointing to the other basic block, which has a single predecessor.
bool CodeGenPrepare::EliminateFallThrough(Function &F) {
bool Changed = false;
// Scan all of the blocks in the function, except for the entry block.
for (Function::iterator I = ++F.begin(), E = F.end(); I != E; ) {
BasicBlock *BB = I++;
// If the destination block has a single pred, then this is a trivial
// edge, just collapse it.
BasicBlock *SinglePred = BB->getSinglePredecessor();
if (!SinglePred || SinglePred == BB) continue;
BranchInst *Term = dyn_cast<BranchInst>(SinglePred->getTerminator());
if (Term && !Term->isConditional()) {
Changed = true;
// Remember if SinglePred was the entry block of the function.
// If so, we will need to move BB back to the entry position.
bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
MergeBasicBlockIntoOnlyPred(BB, this);
if (isEntry && BB != &BB->getParent()->getEntryBlock())
BB->moveBefore(&BB->getParent()->getEntryBlock());
// We have erased a block. Update the iterator.
I = BB;
DEBUG(dbgs() << "Merged:\n"<< *SinglePred << "\n\n\n");
}
}
return Changed;
}
/// EliminateMostlyEmptyBlocks - eliminate blocks that contain only PHI nodes,
/// debug info directives, and an unconditional branch. Passes before isel
/// (e.g. LSR/loopsimplify) often split edges in ways that are non-optimal for

13
llvm/test/CodeGen/ARM/debug-info-branch-folding.ll
View File

@ -3,16 +3,17 @@ target datalayout = "e-p:32:32:32-i1:8:32-i8:8:32-i16:16:32-i32:32:32-i64:32:32-
target triple = "thumbv7-apple-macosx10.6.7"
;CHECK: vadd.f32 q4, q8, q8
;CHECK-NEXT: Ltmp
;CHECK-NEXT: @DEBUG_VALUE: y <- Q4+0
;CHECK-NEXT: @DEBUG_VALUE: x <- Q4+0
;CHECK-NEXT: Ltmp1
;CHECK:@DEBUG_VALUE: x <- Q4+0
;CHECK-NEXT:@DEBUG_VALUE: y <- Q4+0
@.str = external constant [13 x i8]
declare <4 x float> @test0001(float) nounwind readnone ssp
define i32 @main(i32 %argc, i8** nocapture %argv) nounwind ssp {
define i32 @main(i32 %argc, i8** nocapture %argv, i1 %cond) nounwind ssp {
entry:
br label %for.body9
@ -21,7 +22,7 @@ for.body9: ; preds = %for.body9, %entry
tail call void @llvm.dbg.value(metadata !{<4 x float> %add19}, i64 0, metadata !27), !dbg !39
%add20 = fadd <4 x float> undef, <float 0.000000e+00, float 0.000000e+00, float 0.000000e+00, float 1.000000e+00>, !dbg !39
tail call void @llvm.dbg.value(metadata !{<4 x float> %add20}, i64 0, metadata !28), !dbg !39
br i1 undef, label %for.end54, label %for.body9, !dbg !44
br i1 %cond, label %for.end54, label %for.body9, !dbg !44
for.end54: ; preds = %for.body9
%tmp115 = extractelement <4 x float> %add19, i32 1
@ -52,7 +53,7 @@ declare void @llvm.dbg.value(metadata, i64, metadata) nounwind readnone
!7 = metadata !{i32 589860, metadata !2, metadata !"float", null, i32 0, i64 32, i64 32, i64 0, i32 0, i32 4} ; [ DW_TAG_base_type ]
!8 = metadata !{metadata !9}
!9 = metadata !{i32 589857, i64 0, i64 3} ; [ DW_TAG_subrange_type ]
!10 = metadata !{i32 589870, i32 0, metadata !1, metadata !"main", metadata !"main", metadata !"", metadata !1, i32 59, metadata !11, i1 false, i1 true, i32 0, i32 0, i32 0, i32 256, i1 true, i32 (i32, i8**)* @main, null} ; [ DW_TAG_subprogram ]
!10 = metadata !{i32 589870, i32 0, metadata !1, metadata !"main", metadata !"main", metadata !"", metadata !1, i32 59, metadata !11, i1 false, i1 true, i32 0, i32 0, i32 0, i32 256, i1 true, i32 (i32, i8**, i1)* @main, null} ; [ DW_TAG_subprogram ]
!11 = metadata !{i32 589845, metadata !1, metadata !"", metadata !1, i32 0, i64 0, i64 0, i32 0, i32 0, i32 0, metadata !12, i32 0, i32 0} ; [ DW_TAG_subroutine_type ]
!12 = metadata !{metadata !13}
!13 = metadata !{i32 589860, metadata !2, metadata !"int", null, i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ]

6
llvm/test/CodeGen/PowerPC/lbzux.ll
View File

@ -2,7 +2,7 @@ target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f3
target triple = "powerpc64-unknown-linux-gnu"
; RUN: llc < %s | FileCheck %s
define fastcc void @allocateSpace() nounwind {
define fastcc void @allocateSpace(i1 %cond1, i1 %cond2) nounwind {
entry:
%0 = load i8** undef, align 8, !tbaa !0
br i1 undef, label %return, label %lor.lhs.false
@ -20,10 +20,10 @@ while.cond: ; preds = %while.body, %if.the
%idxprom17 = sext i32 0 to i64
%arrayidx18 = getelementptr inbounds i8* %0, i64 %idxprom17
%or = or i32 undef, undef
br i1 false, label %if.end71, label %while.body
br i1 %cond1, label %if.end71, label %while.body
while.body: ; preds = %while.cond
br i1 undef, label %while.cond, label %if.then45
br i1 %cond2, label %while.cond, label %if.then45
if.then45: ; preds = %while.body
%idxprom48139 = zext i32 %or to i64

4
llvm/test/CodeGen/X86/2006-11-12-CSRetCC.ll
View File

@ -52,8 +52,8 @@ entry:
%tmp21 = load double* %tmp20 ; <double> [#uses=1]
%tmp.upgrd.6 = getelementptr [9 x i8]* @str, i32 0, i64 0 ; <i8*> [#uses=1]
%tmp.upgrd.7 = call i32 (i8*, ...)* @printf( i8* %tmp.upgrd.6, double %tmp21, double %tmp19 ) ; <i32> [#uses=0]
br label %return
return: ; preds = %entry
br label %finish
finish:
%retval.upgrd.8 = load i32* %retval ; <i32> [#uses=1]
ret i32 %retval.upgrd.8
}

2
llvm/test/CodeGen/X86/2006-11-17-IllegalMove.ll
View File

@ -1,5 +1,5 @@
; RUN: llc < %s -march=x86-64 > %t
; RUN: grep movb %t | count 2
; RUN: grep movb %t | count 1
; RUN: grep "movzb[wl]" %t

6
llvm/test/CodeGen/X86/2008-01-08-SchedulerCrash.ll
View File

@ -10,10 +10,10 @@
%struct.indexentry = type { i32, i8*, i8*, i8*, i8*, i8* }
define i32 @_bfd_stab_section_find_nearest_line(i32 %offset) nounwind {
define i32 @_bfd_stab_section_find_nearest_line(i32 %offset, i1 %cond) nounwind {
entry:
%tmp910 = add i32 0, %offset ; <i32> [#uses=1]
br i1 true, label %bb951, label %bb917
br i1 %cond, label %bb951, label %bb917
bb917: ; preds = %entry
ret i32 0
@ -21,7 +21,7 @@ bb917: ; preds = %entry
bb951: ; preds = %bb986, %entry
%tmp955 = sdiv i32 0, 2 ; <i32> [#uses=3]
%tmp961 = getelementptr %struct.indexentry* null, i32 %tmp955, i32 0 ; <i32*> [#uses=1]
br i1 true, label %bb986, label %bb967
br i1 %cond, label %bb986, label %bb967
bb967: ; preds = %bb951
ret i32 0

6
llvm/test/Transforms/CodeGenPrepare/basic.ll
View File

@ -5,7 +5,7 @@ target triple = "x86_64-apple-darwin10.0.0"
; CHECK: @test1
; objectsize should fold to a constant, which causes the branch to fold to an
; uncond branch.
; uncond branch. Next, we fold the control flow alltogether.
; rdar://8785296
define i32 @test1(i8* %ptr) nounwind ssp noredzone align 2 {
entry:
@ -13,8 +13,8 @@ entry:
%1 = icmp ugt i64 %0, 3
br i1 %1, label %T, label %trap
; CHECK: entry:
; CHECK-NEXT: br label %T
; CHECK: T:
; CHECK-NOT: br label %
trap: ; preds = %0, %entry
tail call void @llvm.trap() noreturn nounwind

8
llvm/test/Transforms/LoopStrengthReduce/ARM/2012-06-15-lsr-noaddrmode.ll
View File

@ -44,7 +44,7 @@ declare %s* @getstruct() nounwind
; CHECK: @main
; Check that the loop preheader contains no address computation.
; CHECK: %entry
; CHECK: %end_of_chain
; CHECK-NOT: add{{.*}}lsl
; CHECK: ldr{{.*}}lsl #2
; CHECK: ldr{{.*}}lsl #2
@ -65,15 +65,15 @@ while.cond:
while.body:
%v3 = load i32* @ncol, align 4, !tbaa !0
br label %while.cond.i
br label %end_of_chain
while.cond.i:
end_of_chain:
%state.i = getelementptr inbounds %s* %call18, i32 0, i32 0
%v4 = load i32** %state.i, align 4, !tbaa !3
br label %while.cond.i.i
while.cond.i.i:
%counter.0.i.i = phi i32 [ %v3, %while.cond.i ], [ %dec.i.i, %land.rhs.i.i ]
%counter.0.i.i = phi i32 [ %v3, %end_of_chain ], [ %dec.i.i, %land.rhs.i.i ]
%dec.i.i = add nsw i32 %counter.0.i.i, -1
%tobool.i.i = icmp eq i32 %counter.0.i.i, 0
br i1 %tobool.i.i, label %where.exit, label %land.rhs.i.i