[LLVMdev] adapting clamav to LLVM 3.6

[Andreas Cadhalpun]

[Please keep pkg-clamav-devel at lists.alioth.debian.org in CC.]

Hi,

I nearly finished adapting clamav to LLVM 3.6, just one problem remains:
The Sparse Conditional Constant Propagation optimization doesn't work 
anymore.

I have created a small example program demonstrating the problem (attached).

It works fine with LLVM 3.5:
$ make
$ ./test
LLVM module:
---------
; ModuleID = 'test'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"

define i32 @test() {
EntryBlock:
    ret i32 1
}
---------
verifying...
starting test() with JIT...
Result: 1

But it fails with LLVM 3.6:
$ make LLVM=3.6
$ ./test
Pass 'Sparse Conditional Constant Propagation' is not initialized.
Verify if there is a pass dependency cycle.
Required Passes:
Segmentation fault (core dumped)

It's a rather strange error message, because there can't be a dependency 
cycle, if there are no required passes.

The reason for the behavior change is that in LLVM 3.6 the JIT compiler 
got removed so that the MCJIT one is now used by default.
Using the MCJIT compiler in LLVM 3.5 also shows the problem:

$ make MCJIT=1
$ ./test
Pass 'Sparse Conditional Constant Propagation' is not initialized.
Verify if there is a pass dependency cycle.
Required Passes:
Segmentation fault (core dumped)

Disabling the SCCP pass avoids this segfault, but then the optimizations 
are missing (obviously):
$ make SCCP=0 LLVM=3.6
$ ./test
LLVM module:
---------
; ModuleID = 'test'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"

define i32 @test() {
EntryBlock:
    %cond = icmp sle i32 1, 2
    br i1 %cond, label %return, label %test

return:                                           ; preds = %test, 
%EntryBlock
    ret i32 1

test:                                             ; preds = %EntryBlock, 
%test
    %arg = add i32 1, 2
    %cond2 = icmp sle i32 1, %arg
    br i1 %cond2, label %return, label %test
}
---------
verifying...
starting test() with JIT...
Result: 1


Thus I'm wondering if there is a way to make the SCCP pass work with 
MCJIT or is this a bug in LLVM?

Best regards,
Andreas

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LLVM  := 3.5
MCJIT := 0
SCCP  := 1

LLVM_VERSION=$(shell echo $(LLVM) | sed 's/\.//')

CXXFLAGS := -Wall -g -std=c++11 -I/usr/include/llvm-$(LLVM)/ -I/usr/include/llvm-c-$(LLVM) -DLLVM_VERSION=$(LLVM_VERSION) -DUSE_MCJIT=$(MCJIT) -DUSE_SCCP=$(SCCP) -DNDEBUG
LDLIBS := -lLLVM-$(LLVM) -lstdc++ $(LDLIBS)
LDFLAGS := -L/usr/lib/llvm-$(LLVM)/lib

EXAMPLES=test

OBJS=$(addsuffix .o,$(EXAMPLES))

.phony: all clean

all: $(OBJS) $(EXAMPLES)

clean:
	$(RM) $(EXAMPLES) $(OBJS)