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Make simplifycfg reprocess newly formed "br (cond1 | cond2)" conditions

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when simplifying, allowing them to be eagerly turned into switches.  This
is the last step required to get "Example 7" from this blog post:
http://blog.regehr.org/archives/320

On X86, we now generate this machine code, which (to my eye) seems better
than the ICC generated code:

_crud:                                  ## @crud
## BB#0:                                ## %entry
	cmpb	$33, %dil
	jb	LBB0_4
## BB#1:                                ## %switch.early.test
	addb	$-34, %dil
	cmpb	$58, %dil
	ja	LBB0_3
## BB#2:                                ## %switch.early.test
	movzbl	%dil, %eax
	movabsq	$288230376537592865, %rcx ## imm = 0x400000017001421
	btq	%rax, %rcx
	jb	LBB0_4
LBB0_3:                                 ## %lor.rhs
	xorl	%eax, %eax
	ret
LBB0_4:                                 ## %lor.end
	movl	$1, %eax
	ret



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121690 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-12-13 07:00:06 +00:00
parent 021c9d3bd4
commit daa02ab70c
2 changed files with 78 additions and 6 deletions
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17
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -1357,7 +1357,7 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
// must be at the front of the block.
BasicBlock::iterator FrontIt = BB->front();
// Ignore dbg intrinsics.
while(isa<DbgInfoIntrinsic>(FrontIt))
while (isa<DbgInfoIntrinsic>(FrontIt))
++FrontIt;
// Allow a single instruction to be hoisted in addition to the compare
@ -1441,7 +1441,7 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
UsedValues.erase(Pair.first);
if (UsedValues.empty()) break;
if (Instruction* I = dyn_cast<Instruction>(Pair.first)) {
if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
OI != OE; ++OI)
Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
@ -1469,9 +1469,16 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
// If we need to invert the condition in the pred block to match, do so now.
if (InvertPredCond) {
Value *NewCond =
BinaryOperator::CreateNot(PBI->getCondition(),
Value *NewCond = PBI->getCondition();
if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
CmpInst *CI = cast<CmpInst>(NewCond);
CI->setPredicate(CI->getInversePredicate());
} else {
NewCond = BinaryOperator::CreateNot(NewCond,
PBI->getCondition()->getName()+".not", PBI);
}
PBI->setCondition(NewCond);
BasicBlock *OldTrue = PBI->getSuccessor(0);
BasicBlock *OldFalse = PBI->getSuccessor(1);
@ -1507,7 +1514,7 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
AddPredecessorToBlock(FalseDest, PredBlock, BB);
PBI->setSuccessor(1, FalseDest);
}
return true;
return SimplifyCFG(PBI->getParent()) | true;
}
return false;
}

67
test/Transforms/SimplifyCFG/switch_create.ll
View File

@ -203,5 +203,70 @@ if.end: ; preds = %entry
; CHECK: i8 97, label %if.then
; CHECK: ]
; CHECK: %A = phi i32 [ 0, %entry ], [ 42, %switch.early.test ], [ 42, %N ], [ 42, %switch.early.test ]
}
define i32 @test9(i8 zeroext %c) nounwind ssp noredzone {
entry:
%cmp = icmp ult i8 %c, 33
br i1 %cmp, label %lor.end, label %lor.lhs.false
lor.lhs.false: ; preds = %entry
%cmp4 = icmp eq i8 %c, 46
br i1 %cmp4, label %lor.end, label %lor.lhs.false6
lor.lhs.false6: ; preds = %lor.lhs.false
%cmp9 = icmp eq i8 %c, 44
br i1 %cmp9, label %lor.end, label %lor.lhs.false11
lor.lhs.false11: ; preds = %lor.lhs.false6
%cmp14 = icmp eq i8 %c, 58
br i1 %cmp14, label %lor.end, label %lor.lhs.false16
lor.lhs.false16: ; preds = %lor.lhs.false11
%cmp19 = icmp eq i8 %c, 59
br i1 %cmp19, label %lor.end, label %lor.lhs.false21
lor.lhs.false21: ; preds = %lor.lhs.false16
%cmp24 = icmp eq i8 %c, 60
br i1 %cmp24, label %lor.end, label %lor.lhs.false26
lor.lhs.false26: ; preds = %lor.lhs.false21
%cmp29 = icmp eq i8 %c, 62
br i1 %cmp29, label %lor.end, label %lor.lhs.false31
lor.lhs.false31: ; preds = %lor.lhs.false26
%cmp34 = icmp eq i8 %c, 34
br i1 %cmp34, label %lor.end, label %lor.lhs.false36
lor.lhs.false36: ; preds = %lor.lhs.false31
%cmp39 = icmp eq i8 %c, 92
br i1 %cmp39, label %lor.end, label %lor.rhs
lor.rhs: ; preds = %lor.lhs.false36
%cmp43 = icmp eq i8 %c, 39
br label %lor.end
lor.end: ; preds = %lor.rhs, %lor.lhs.false36, %lor.lhs.false31, %lor.lhs.false26, %lor.lhs.false21, %lor.lhs.false16, %lor.lhs.false11, %lor.lhs.false6, %lor.lhs.false, %entry
%0 = phi i1 [ true, %lor.lhs.false36 ], [ true, %lor.lhs.false31 ], [ true, %lor.lhs.false26 ], [ true, %lor.lhs.false21 ], [ true, %lor.lhs.false16 ], [ true, %lor.lhs.false11 ], [ true, %lor.lhs.false6 ], [ true, %lor.lhs.false ], [ true, %entry ], [ %cmp43, %lor.rhs ]
%conv46 = zext i1 %0 to i32
ret i32 %conv46
; CHECK: @test9
; CHECK: %cmp = icmp ult i8 %c, 33
; CHECK: br i1 %cmp, label %lor.end, label %switch.early.test
; CHECK: switch.early.test:
; CHECK: switch i8 %c, label %lor.rhs [
; CHECK: i8 46, label %lor.end
; CHECK: i8 44, label %lor.end
; CHECK: i8 58, label %lor.end
; CHECK: i8 59, label %lor.end
; CHECK: i8 60, label %lor.end
; CHECK: i8 62, label %lor.end
; CHECK: i8 34, label %lor.end
; CHECK: i8 92, label %lor.end
; CHECK: i8 39, label %lor.end
; CHECK: ]
}