[LLVMdev] Deleting Instructions after Intrinsic Creation

aditya vishnubhotla vvaditya12 at yahoo.com
Tue Mar 4 05:37:06 PST 2008

I tried creating  intrinsics which
are to be placeholders for a set of instructions which
should not be executed by the backend.

I want to retain only intrinsic,phi and terminator
instructions in a basic block.
I have taken care of the external dependencies of
basic block.
How do I delete the rest of the instructions?

Thank You


Below is the section of LLVM IR after intrinsic
creation (Instructions to be deleted  have only
internal uses):

define i32 @main() nounwind  {
        %year.i = alloca i32            ; <i32*>
        %tmp2.i = call i32 (i8*, ...)* @printf( i8*
noalias  getelementptr ([15 x i8]* @.str2, i32 0, i32
0) ) nounwind                 ; <i32> [#uses=0]
        %tmp4.i = call i32 (i8*, ...)* @scanf( i8*
noalias  getelementptr ([3 x i8]* @.str3, i32 0, i32
0), i32* %year.i ) nounwind             ; <i32>
        %tmp5.i = load i32* %year.i, align 4          
 ; <i32> [#uses=3]
        %tmp12.i = sitofp i32 %tmp5.i to double       
 ; <double> [#uses=1]
        %tmp3.i = sub double %tmp12.i, 1.000000e+00   
         ; <double> [#uses=3]
        %tmp4.i1 = fdiv double %tmp3.i, 4.000000e+00  
         ; <double> [#uses=1]
        %tmp45.i = fptosi double %tmp4.i1 to i32      
         ; <i32> [#uses=1]
        %tmp9.i = fdiv double %tmp3.i, 1.000000e+02   
         ; <double> [#uses=1]
        %tmp910.i = fptosi double %tmp9.i to i32      
         ; <i32> [#uses=1]
        %tmp14.i = fdiv double %tmp3.i, 4.000000e+02  
         ; <double> [#uses=1]
        %tmp1415.i = fptosi double %tmp14.i to i32    
         ; <i32> [#uses=1]
        %tmp18.i = add i32 %tmp45.i, %tmp5.i          
 ; <i32> [#uses=1]
        %tmp20.i = sub i32 %tmp18.i, %tmp910.i        
 ; <i32> [#uses=1]
        %tmp22.i = add i32 %tmp20.i, %tmp1415.i       
 ; <i32> [#uses=1]
        %tmp23.i = srem i32 %tmp22.i, 7         ;
<i32> [#uses=0]
        %tmp2.i2 = and i32 %tmp5.i, 3           ;
<i32> [#uses=1]
        %tmp3.i3 = icmp eq i32 %tmp2.i2, 0            
 ; <i1> [#uses=0]
        %migrate_begin = call i32 (...)*
@llvm.migrate_begin( )         ; <i32> [#uses=2]
        %migrate_end = call i32
@llvm.migrate_end_1.i32( i32 %migrate_begin )         
 ; <i32> [#uses=5]
        %migrate_end1 = call i1
@llvm.migrate_end_1.i1( i32 %migrate_begin )          
 ; <i1> [#uses=1]
        br i1 %migrate_end1, label %bb.i, label
Section of code used to delete instructions:

for(BasicBlock::iterator i=
	if(!((i->isTerminator()) || (isa<CallInst>(i))))
for(BasicBlock::iterator bi=

(gdb) bt
#0  llvm::AssemblyWriter::printInstruction
(this=0xbfa1a75c, I=@0x877b488) at AsmWriter.cpp:1378
#1  0x085b2ece in llvm::AssemblyWriter::write
(this=0xbfa1a75c, I=0x877b488) at AsmWriter.cpp:741
#2  0x085adb0f in llvm::Instruction::print
(this=0x877b488, o=@0x8794f48, AAW=0x0) at
#3  0x085b5bf2 in llvm::Instruction::print
(this=0x877b488, OS=@0x8794f48) at
#4  0x08357c13 in llvm::operator<< (OS=@0x8794f48,
V=@0x877b488) at
#5  0x0863ceb5 in (anonymous
namespace)::Verifier::WriteValue (this=0x8794f18,
V=0x877b488) at Verifier.cpp:272
#6  0x0863d139 in (anonymous
namespace)::Verifier::CheckFailed (this=0x8794f18,
Message=@0xbfa1a878, V1=0x877b488, V2=0x0, V3=0x0,
V4=0x0) at Verifier.cpp:292
#7  0x08636ba2 in (anonymous
(this=0x8794f18, I=@0x877b488) at Verifier.cpp:1077
#8  0x08637807 in (anonymous
(this=0x8794f18, AI=@0x877b488) at Verifier.cpp:1037
#9  0x0863d75e in llvm::InstVisitor<(anonymous
namespace)::Verifier, void>::visitAllocaInst
(this=0x8794f18, I=@0x877b488) at
#10 0x0863d778 in llvm::InstVisitor<(anonymous
namespace)::Verifier, void>::visitAlloca
(this=0x8794f18, I=@0x877b488) at
#11 0x0863df45 in llvm::InstVisitor<(anonymous
namespace)::Verifier, void>::visit (this=0x8794f18,
I=@0x877b488) at
#12 0x0863e1d1 in llvm::InstVisitor<(anonymous
void>::visit<llvm::ilist_iterator<llvm::Instruction> >
(this=0x8794f18, Start=
= {<> = {<No data fields>}, <No data fields>}, NodePtr
= 0x877b4f8}, End=
= {<> = {<No data fields>}, <No data fields>}, NodePtr
= 0x877b4c8}) at
#13 0x0863e248 in llvm::InstVisitor<(anonymous
namespace)::Verifier, void>::visit (this=0x8794f18,
BB=@0x8776e80) at
#14 0x0863e293 in llvm::InstVisitor<(anonymous
void>::visit<llvm::ilist_iterator<llvm::BasicBlock> >
(this=0x8794f18, Start=
= {<> = {<No data fields>}, <No data fields>}, NodePtr
= 0x8776ee8}, End=
= {<> = {<No data fields>}, <No data fields>}, NodePtr
= 0x8776ea8}) at
#15 0x0863e4b0 in llvm::InstVisitor<(anonymous
namespace)::Verifier, void>::visit (this=0x8794f18,
F=@0x8777638) at
#16 0x0863e4ff in (anonymous
namespace)::Verifier::runOnFunction (this=0x8794f18,
F=@0x8777638) at Verifier.cpp:155
#17 0x0860e692 in llvm::FPPassManager::runOnFunction
(this=0x8793ca8, F=@0x8777638) at PassManager.cpp:1171
#18 0x0860e83e in llvm::FPPassManager::runOnModule
(this=0x8793ca8, M=@0x8773d10) at PassManager.cpp:1191
#19 0x0860e362 in llvm::MPPassManager::runOnModule
(this=0x87731d8, M=@0x8773d10) at PassManager.cpp:1240
#20 0x0860e518 in llvm::PassManagerImpl::run
(this=0x87766b8, M=@0x8773d10) at PassManager.cpp:1313
#21 0x0860e56a in llvm::PassManager::run
(this=0xbfa1ac28, M=@0x8773d10) at
#22 0x0836680d in main (argc=13, argv=0xbfa1ae14) at

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