[llvm] r259730 - [SimplifyCFG] Fix for "endless" loop after dead code removal (Alternative to
Gerolf Hoflehner via llvm-commits
llvm-commits at lists.llvm.org
Wed Feb 3 15:54:26 PST 2016
Author: ghoflehner
Date: Wed Feb 3 17:54:25 2016
New Revision: 259730
URL: http://llvm.org/viewvc/llvm-project?rev=259730&view=rev
Log:
[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
Added:
llvm/trunk/test/Transforms/SimplifyCFG/InfLoop.ll
Modified:
llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=259730&r1=259729&r2=259730&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Wed Feb 3 17:54:25 2016
@@ -508,8 +508,10 @@ private:
// Keep a stack (SmallVector for efficiency) for depth-first traversal
SmallVector<Value *, 8> DFT;
+ SmallPtrSet<Value *, 8> Visited;
// Initialize
+ Visited.insert(V);
DFT.push_back(V);
while(!DFT.empty()) {
@@ -518,8 +520,10 @@ private:
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));
- DFT.push_back(I->getOperand(0));
+ if (Visited.insert(I->getOperand(1)).second)
+ DFT.push_back(I->getOperand(1));
+ if (Visited.insert(I->getOperand(0)).second)
+ DFT.push_back(I->getOperand(0));
continue;
}
Added: llvm/trunk/test/Transforms/SimplifyCFG/InfLoop.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/InfLoop.ll?rev=259730&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/InfLoop.ll (added)
+++ llvm/trunk/test/Transforms/SimplifyCFG/InfLoop.ll Wed Feb 3 17:54:25 2016
@@ -0,0 +1,101 @@
+; 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 }
+
+ at 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
+}
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