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llvm-project/llvm/test/Transforms/SimplifyCFG/InfLoop.ll

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[SimplifyCFG] Fix for "endless" loop after dead code removal (Alternative to D16251) Summary: This is a simpler fix to the problem than the dominator approach in http://reviews.llvm.org/D16251. It adds only values into the gather() while loop that have been seen before. The actual endless loop is in the constant compare gather() routine in Utils/SimplifyCFG.cpp. The same value ret.0.off0.i is pushed back into the queue: %.ret.0.off0.i = or i1 %.ret.0.off0.i, %cmp10.i Here is what happens at the IR level: for.cond.i: ; preds = %if.end6.i, %if.end.i54 %ix.0.i = phi i32 [ 0, %if.end.i54 ], [ %inc.i55, %if.end6.i ] %ret.0.off0.i = phi i1 [false, %if.end.i54], [%.ret.0.off0.i, %if.end6.i] <<< %cmp2.i = icmp ult i32 %ix.0.i, %11 br i1 %cmp2.i, label %for.body.i, label %LBJ_TmpSimpleNeedExt.exit if.end6.i: ; preds = %for.body.i %cmp10.i = icmp ugt i32 %conv.i, %add9.i %.ret.0.off0.i = or i1 %ret.0.off0.i, %cmp10.i <<< When if.end.i54 gets eliminated which removes the definition of ret.0.off0.i. The result is the expression %.ret.0.off0.i = or i1 %.ret.0.off0.i, %cmp10.i (Note the first ‘or’ operand is now %.ret.0.off0.i, and *NOT* %ret.0.off0.i). And now there is use of .ret.0.off0.i before a definition which triggers the “endless” loop in gather(): while(!DFT.empty()) { V = DFT.pop_back_val(); // V is .ret.0.off0.i if (Instruction *I = dyn_cast<Instruction>(V)) { // If it is a || (or && depending on isEQ), process the operands. if (I->getOpcode() == (isEQ ? Instruction::Or : Instruction::And)) { DFT.push_back(I->getOperand(1)); // This is now .ret.0.off0.i also DFT.push_back(I->getOperand(0)); continue; // “endless loop” for .ret.0.off0.i } Reviewers: reames, ahatanak Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D16839 llvm-svn: 259730
2016-02-04 07:54:25 +08:00
; RUN: opt < %s -simplifycfg -disable-output
; END.
target datalayout = "e-m:o-p:32:32-f64:32:64-v64:32:64-v128:32:128-a:0:32-n32-S32"
target triple = "thumbv7-apple-ios9.0.0"
%struct.anon = type { %struct.anon.0, i32, i32, %union.T1 }
%struct.anon.0 = type { i32, [256 x i32], [256 x i8] }
%union.T1 = type { %struct.F}
%struct.F = type { i32 }
@U = internal global %struct.anon zeroinitializer, align 4
define void @main() {
entry:
%0 = load i32, i32* getelementptr inbounds (%struct.anon, %struct.anon* @U, i32 0, i32 2), align 4
%cmp.i = icmp eq i32 %0, -1
br i1 %cmp.i, label %if.then, label %if.end
if.then: ; preds = %entry
br label %if.end
if.end: ; preds = %entry, %if.then
%1 = load i32, i32* getelementptr inbounds (%struct.anon, %struct.anon* @U, i32 0, i32 2), align 4
%bf.load = load i32, i32* getelementptr inbounds (%struct.anon, %struct.anon* @U, i32 0, i32 3, i32 0, i32 0), align 4
%cmp = icmp slt i32 %0, 0
br i1 %cmp, label %if.end7, label %cond.false
cond.false: ; preds = %if.end
%add = and i32 %bf.load, 30
%shl = add nuw nsw i32 %add, 2
br label %if.end7
if.end7: ; preds = %if.end, %cond.false
%2 = icmp eq i32 %0, 1
br i1 %2, label %if.then9, label %if.else10
if.then9: ; preds = %if.end7
br label %if.end29
if.else10: ; preds = %if.end7
%cmp11 = icmp ugt i32 %0, 13
br i1 %cmp11, label %if.then12, label %if.else14
if.then12: ; preds = %if.else10
br label %if.end26
if.else14: ; preds = %if.else10
%tobool = icmp eq i1 %2, 0
br i1 %tobool, label %lor.rhs, label %if.then18
lor.rhs: ; preds = %if.else14
%tobool.not.i = icmp eq i1 %2, 0
br i1 %tobool.not.i, label %if.else21, label %if.end.i54
if.end.i54: ; preds = %lor.rhs
br label %for.cond.i
for.cond.i: ; preds = %if.end6.i, %if.end.i54
%ix.0.i = phi i32 [ 0, %if.end.i54 ], [ %inc.i55, %if.end6.i ]
%ret.0.off0.i = phi i1 [ false, %if.end.i54 ], [ %.ret.0.off0.i, %if.end6.i ]
%cmp2.i = icmp ult i32 %ix.0.i, 2
br i1 %cmp2.i, label %for.body.i, label %TmpSimpleNeedExt.exit
for.body.i: ; preds = %for.cond.i
%arrayidx.i = getelementptr inbounds %struct.anon, %struct.anon* @U, i32 0, i32 0, i32 2, i32 %ix.0.i
%elt = load i8, i8* %arrayidx.i, align 1
%cmp3.i = icmp sgt i8 %elt, 7
br i1 %cmp3.i, label %if.else21, label %if.end6.i
if.end6.i: ; preds = %for.body.i
%cmp10.i = icmp ugt i8 %elt, 59
%.ret.0.off0.i = or i1 %ret.0.off0.i, %cmp10.i
%inc.i55 = add i32 %ix.0.i, 1
br label %for.cond.i
TmpSimpleNeedExt.exit: ; preds = %for.body.i
br i1 %ret.0.off0.i, label %if.then18, label %if.else21
if.then18: ; preds = %if.else14, %TmpSimpleNeedExt.exit
br label %if.end26
if.else21: ; preds = %for.body.i, %lor.rhs, %TmpSimpleNeedExt.exit
br label %if.end26
if.end26: ; preds = %if.then18, %if.else21, %if.then12
%cmp.i51 = icmp slt i32 %0, 7
br i1 %cmp.i51, label %if.then.i, label %if.end.i
if.then.i: ; preds = %if.end26
br label %if.end.i
if.end.i: ; preds = %if.then.i, %if.end26
br label %if.end29
if.then2.i: ; preds = %if.end.i
br label %if.end29
if.end29: ; preds = %if.end.i, %if.then2.i, %if.then9
ret void
}