[llvm-branch-commits] [llvm] 6cdf6e5 - BPF: avoid NE/EQ loop exit condition
Tom Stellard via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Fri Aug 6 12:46:11 PDT 2021
Author: Yonghong Song
Date: 2021-08-06T12:45:53-07:00
New Revision: 6cdf6e50442cc2c9d19a241ab61db83cde80d416
URL: https://github.com/llvm/llvm-project/commit/6cdf6e50442cc2c9d19a241ab61db83cde80d416
DIFF: https://github.com/llvm/llvm-project/commit/6cdf6e50442cc2c9d19a241ab61db83cde80d416.diff
LOG: BPF: avoid NE/EQ loop exit condition
Kuniyuki Iwashima reported in [1] that llvm compiler may
convert a loop exit condition with "i < bound" to "i != bound", where
"i" is the loop index variable and "bound" is the upper bound.
In case that "bound" is not a constant, verifier will always have "i != bound"
true, which will cause verifier failure since to verifier this is
an infinite loop.
The fix is to avoid transforming "i < bound" to "i != bound".
In llvm, the transformation is done by IndVarSimplify pass.
The compiler checks loop condition cost (i = i + 1) and if the
cost is lower, it may transform "i < bound" to "i != bound".
This patch implemented getArithmeticInstrCost() in BPF TargetTransformInfo
class to return a higher cost for such an operation, which
will prevent the transformation for the test case
added in this patch.
[1] https://lore.kernel.org/netdev/1994df05-8f01-371f-3c3b-d33d7836878c@fb.com/
Differential Revision: https://reviews.llvm.org/D107483
(cherry picked from commit e52946b9ababcbf8e6f40b1b15900ae2e795a1c6)
Added:
llvm/test/CodeGen/BPF/loop-exit-cond.ll
Modified:
llvm/lib/Target/BPF/BPFTargetTransformInfo.h
Removed:
################################################################################
diff --git a/llvm/lib/Target/BPF/BPFTargetTransformInfo.h b/llvm/lib/Target/BPF/BPFTargetTransformInfo.h
index 3bc5556a62f4d..417e8b6ffec37 100644
--- a/llvm/lib/Target/BPF/BPFTargetTransformInfo.h
+++ b/llvm/lib/Target/BPF/BPFTargetTransformInfo.h
@@ -54,6 +54,24 @@ class BPFTTIImpl : public BasicTTIImplBase<BPFTTIImpl> {
return BaseT::getCmpSelInstrCost(Opcode, ValTy, CondTy, VecPred, CostKind,
I);
}
+
+ InstructionCost getArithmeticInstrCost(
+ unsigned Opcode, Type *Ty,
+ TTI::TargetCostKind CostKind = TTI::TCK_RecipThroughput,
+ TTI::OperandValueKind Opd1Info = TTI::OK_AnyValue,
+ TTI::OperandValueKind Opd2Info = TTI::OK_AnyValue,
+ TTI::OperandValueProperties Opd1PropInfo = TTI::OP_None,
+ TTI::OperandValueProperties Opd2PropInfo = TTI::OP_None,
+ ArrayRef<const Value *> Args = ArrayRef<const Value *>(),
+ const Instruction *CxtI = nullptr) {
+ int ISD = TLI->InstructionOpcodeToISD(Opcode);
+ if (ISD == ISD::ADD && CostKind == TTI::TCK_RecipThroughput)
+ return SCEVCheapExpansionBudget.getValue() + 1;
+
+ return BaseT::getArithmeticInstrCost(Opcode, Ty, CostKind, Opd1Info,
+ Opd2Info, Opd1PropInfo,
+ Opd2PropInfo);
+ }
};
} // end namespace llvm
diff --git a/llvm/test/CodeGen/BPF/loop-exit-cond.ll b/llvm/test/CodeGen/BPF/loop-exit-cond.ll
new file mode 100644
index 0000000000000..9883367a5b449
--- /dev/null
+++ b/llvm/test/CodeGen/BPF/loop-exit-cond.ll
@@ -0,0 +1,131 @@
+; RUN: opt -O2 -S -o %t1 < %s
+; RUN: llc -march=bpf -mcpu=v3 %t1 -o - | FileCheck %s
+;
+; Source code:
+; typedef unsigned long u64;
+; void foo(char *data, int idx, u64 *);
+; int test(int len, char *data) {
+; if (len < 100) {
+; for (int i = 1; i < len; i++) {
+; u64 d[1];
+; d[0] = data[0] ?: '0';
+; foo("%c", i, d);
+; }
+; }
+; return 0;
+; }
+; Compilation flag:
+; clang -target bpf -O2 -S -emit-llvm -Xclang -disable-llvm-passes test.c
+
+; ModuleID = 'test.c'
+source_filename = "test.c"
+target datalayout = "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128"
+target triple = "bpf"
+
+ at .str = private unnamed_addr constant [3 x i8] c"%c\00", align 1
+
+; Function Attrs: nounwind
+define dso_local i32 @test(i32 %len, i8* %data) #0 {
+entry:
+ %len.addr = alloca i32, align 4
+ %data.addr = alloca i8*, align 8
+ %i = alloca i32, align 4
+ %d = alloca [1 x i64], align 8
+ store i32 %len, i32* %len.addr, align 4, !tbaa !3
+ store i8* %data, i8** %data.addr, align 8, !tbaa !7
+ %0 = load i32, i32* %len.addr, align 4, !tbaa !3
+ %cmp = icmp slt i32 %0, 100
+ br i1 %cmp, label %if.then, label %if.end
+
+if.then: ; preds = %entry
+ %1 = bitcast i32* %i to i8*
+ call void @llvm.lifetime.start.p0i8(i64 4, i8* %1) #3
+ store i32 1, i32* %i, align 4, !tbaa !3
+ br label %for.cond
+
+for.cond: ; preds = %for.inc, %if.then
+ %2 = load i32, i32* %i, align 4, !tbaa !3
+ %3 = load i32, i32* %len.addr, align 4, !tbaa !3
+ %cmp1 = icmp slt i32 %2, %3
+ br i1 %cmp1, label %for.body, label %for.cond.cleanup
+
+; CHECK: w[[LEN:[0-9]+]] = w1
+; CHECK: w[[IDX:[0-9]+]] += 1
+; CHECK-NEXT: w[[IDX]] s< w[[LEN]] goto
+
+for.cond.cleanup: ; preds = %for.cond
+ %4 = bitcast i32* %i to i8*
+ call void @llvm.lifetime.end.p0i8(i64 4, i8* %4) #3
+ br label %for.end
+
+for.body: ; preds = %for.cond
+ %5 = bitcast [1 x i64]* %d to i8*
+ call void @llvm.lifetime.start.p0i8(i64 8, i8* %5) #3
+ %6 = load i8*, i8** %data.addr, align 8, !tbaa !7
+ %arrayidx = getelementptr inbounds i8, i8* %6, i64 0
+ %7 = load i8, i8* %arrayidx, align 1, !tbaa !9
+ %conv = sext i8 %7 to i32
+ %tobool = icmp ne i32 %conv, 0
+ br i1 %tobool, label %cond.true, label %cond.false
+
+cond.true: ; preds = %for.body
+ br label %cond.end
+
+cond.false: ; preds = %for.body
+ br label %cond.end
+
+cond.end: ; preds = %cond.false, %cond.true
+ %cond = phi i32 [ %conv, %cond.true ], [ 48, %cond.false ]
+ %conv2 = sext i32 %cond to i64
+ %arrayidx3 = getelementptr inbounds [1 x i64], [1 x i64]* %d, i64 0, i64 0
+ store i64 %conv2, i64* %arrayidx3, align 8, !tbaa !10
+ %8 = load i32, i32* %i, align 4, !tbaa !3
+ %arraydecay = getelementptr inbounds [1 x i64], [1 x i64]* %d, i64 0, i64 0
+ call void @foo(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32 %8, i64* %arraydecay)
+ %9 = bitcast [1 x i64]* %d to i8*
+ call void @llvm.lifetime.end.p0i8(i64 8, i8* %9) #3
+ br label %for.inc
+
+for.inc: ; preds = %cond.end
+ %10 = load i32, i32* %i, align 4, !tbaa !3
+ %inc = add nsw i32 %10, 1
+ store i32 %inc, i32* %i, align 4, !tbaa !3
+ br label %for.cond, !llvm.loop !12
+
+for.end: ; preds = %for.cond.cleanup
+ br label %if.end
+
+if.end: ; preds = %for.end, %entry
+ ret i32 0
+}
+
+; Function Attrs: argmemonly nofree nosync nounwind willreturn
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1
+
+declare dso_local void @foo(i8*, i32, i64*) #2
+
+; Function Attrs: argmemonly nofree nosync nounwind willreturn
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1
+
+attributes #0 = { nounwind "frame-pointer"="all" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
+attributes #1 = { argmemonly nofree nosync nounwind willreturn }
+attributes #2 = { "frame-pointer"="all" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
+attributes #3 = { nounwind }
+
+!llvm.module.flags = !{!0, !1}
+!llvm.ident = !{!2}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 7, !"frame-pointer", i32 2}
+!2 = !{!"clang version 14.0.0 (https://github.com/llvm/llvm-project.git 8385de118443144518c9fba8b3d831d9076e746b)"}
+!3 = !{!4, !4, i64 0}
+!4 = !{!"int", !5, i64 0}
+!5 = !{!"omnipotent char", !6, i64 0}
+!6 = !{!"Simple C/C++ TBAA"}
+!7 = !{!8, !8, i64 0}
+!8 = !{!"any pointer", !5, i64 0}
+!9 = !{!5, !5, i64 0}
+!10 = !{!11, !11, i64 0}
+!11 = !{!"long", !5, i64 0}
+!12 = distinct !{!12, !13}
+!13 = !{!"llvm.loop.mustprogress"}
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