Hi all,
I'm writting following LLVM assembly:
; ModuleID = 'structaccess.ll'
%struct._anon0 = type <{ i32, i32, i32 }>
@s = common global %struct._anon0 zeroinitializer
define arm_aapcscc void @foo() nounwind {
L.entry:
store i32 5, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32
0)
store i32 10, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32
1)
%0 = load i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 0)
%1 = load i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 1)
%2 = add i32 %0, %1
store i32 %2, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32
2)
ret void
}
Using 'opt' utility as follows :
opt -O2 structaccess.ll -S -o structaccess-opt.ll
I've got following code for structaccess-opt.ll file:
; ModuleID = 'structaccess.ll'
%struct._anon0 = type <{ i32, i32, i32 }>
@s = common global %struct._anon0 zeroinitializer
define arm_aapcscc void @foo() nounwind {
L.entry:
store i32 5, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32
0)
store i32 10, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32
1)
%0 = load i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 0)
%1 = add i32 %0, 10
store i32 %1, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32
2)
ret void
}
I would have expected constant 5 to be propagated by 'opt' to its use
and
thus LLVM assembly after opt to be :
; ModuleID = 'structaccess.ll'
%struct._anon0 = type <{ i32, i32, i32 }>
@s = common global %struct._anon0 zeroinitializer
define arm_aapcscc void @foo() nounwind {
L.entry:
store i32 5, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32
0)
store i32 10, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32
1)
store i32 15, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32
2)
ret void
}
Can someone explain me why this is not the case ?
Note that C equivalent would be something like:
struct {
int x, y, z;
} s;
void foo()
{
s.x = 5 ;
s.y = 10 ;
s.z = s.x + s.y ;
}
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Duncan Sands
2011-Oct-18 13:42 UTC
[LLVMdev] LLVM constant propagation optimization question
Hi Seb,> I'm writting following LLVM assembly: > > ; ModuleID = 'structaccess.ll' >not having a data layout string in your module disables many optimizations. Ciao, Duncan.> %struct._anon0 = type <{ i32, i32, i32 }> > > @s = common global %struct._anon0 zeroinitializer > > define arm_aapcscc void @foo() nounwind { > L.entry: > store i32 5, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 0) > store i32 10, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 1) > %0 = load i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 0) > %1 = load i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 1) > %2 = add i32 %0, %1 > store i32 %2, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 2) > ret void > } > > Using 'opt' utility as follows : > > opt -O2 structaccess.ll -S -o structaccess-opt.ll > > I've got following code for structaccess-opt.ll file: > > ; ModuleID = 'structaccess.ll' > > %struct._anon0 = type <{ i32, i32, i32 }> > > @s = common global %struct._anon0 zeroinitializer > > define arm_aapcscc void @foo() nounwind { > L.entry: > store i32 5, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 0) > store i32 10, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 1) > %0 = load i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 0) > %1 = add i32 %0, 10 > store i32 %1, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 2) > ret void > } > > I would have expected constant 5 to be propagated by 'opt' to its use and thus > LLVM assembly after opt to be : > > ; ModuleID = 'structaccess.ll' > > %struct._anon0 = type <{ i32, i32, i32 }> > > @s = common global %struct._anon0 zeroinitializer > > define arm_aapcscc void @foo() nounwind { > L.entry: > store i32 5, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 0) > store i32 10, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 1) > store i32 15, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 2) > ret void > } > > Can someone explain me why this is not the case ? > > Note that C equivalent would be something like: > > struct { > int x, y, z; > } s; > > void foo() > { > s.x = 5 ; > s.y = 10 ; > s.z = s.x + s.y ; > } > > > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
Hi Duncan, What do you mean by "a data layout string in your module" ? Best Regards Seb 2011/10/18 Duncan Sands <baldrick at free.fr>> Hi Seb, > > > I'm writting following LLVM assembly: > > > > ; ModuleID = 'structaccess.ll' > > > > not having a data layout string in your module disables many optimizations. > > Ciao, Duncan. > > > %struct._anon0 = type <{ i32, i32, i32 }> > > > > @s = common global %struct._anon0 zeroinitializer > > > > define arm_aapcscc void @foo() nounwind { > > L.entry: > > store i32 5, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, > i32 0) > > store i32 10, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, > i32 1) > > %0 = load i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 > 0) > > %1 = load i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 > 1) > > %2 = add i32 %0, %1 > > store i32 %2, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, > i32 2) > > ret void > > } > > > > Using 'opt' utility as follows : > > > > opt -O2 structaccess.ll -S -o structaccess-opt.ll > > > > I've got following code for structaccess-opt.ll file: > > > > ; ModuleID = 'structaccess.ll' > > > > %struct._anon0 = type <{ i32, i32, i32 }> > > > > @s = common global %struct._anon0 zeroinitializer > > > > define arm_aapcscc void @foo() nounwind { > > L.entry: > > store i32 5, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, > i32 0) > > store i32 10, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, > i32 1) > > %0 = load i32* getelementptr inbounds (%struct._anon0* @s, i32 0, i32 > 0) > > %1 = add i32 %0, 10 > > store i32 %1, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, > i32 2) > > ret void > > } > > > > I would have expected constant 5 to be propagated by 'opt' to its use and > thus > > LLVM assembly after opt to be : > > > > ; ModuleID = 'structaccess.ll' > > > > %struct._anon0 = type <{ i32, i32, i32 }> > > > > @s = common global %struct._anon0 zeroinitializer > > > > define arm_aapcscc void @foo() nounwind { > > L.entry: > > store i32 5, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, > i32 0) > > store i32 10, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, > i32 1) > > store i32 15, i32* getelementptr inbounds (%struct._anon0* @s, i32 0, > i32 2) > > ret void > > } > > > > Can someone explain me why this is not the case ? > > > > Note that C equivalent would be something like: > > > > struct { > > int x, y, z; > > } s; > > > > void foo() > > { > > s.x = 5 ; > > s.y = 10 ; > > s.z = s.x + s.y ; > > } > > > > > > > > _______________________________________________ > > LLVM Developers mailing list > > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20111018/acd09f99/attachment.html>