[LLVMdev] 16bit loads being promoted to 32bit?

[Villmow, Micah]

I have the following function:

define void @test_fc_0_kernel(i16 signext %x, i16 signext %y, i16
addrspace(11)* %input, i32 addrspace(11)* %result) {

entry:

            %call = tail call i32 @get_id(i32 0)                       ;
<i32> [#uses=2]

            %cmp = icmp slt i16 %x, %y                  ; <i1> [#uses=1]

            br i1 %cmp, label %if.then, label %if.end

 

if.end:               ; preds = %entry

            ret void

 

if.then:              ; preds = %entry

            %arrayidx = getelementptr i32 addrspace(11)* %result, i32
%call               ; <i32 addrspace(11)*> [#uses=1]

            %arrayidx7 = getelementptr i16 addrspace(11)* %input, i32
%call              ; <i16 addrspace(11)*> [#uses=1]

            %tmp8 = load i16 addrspace(11)* %arrayidx7
; <i16> [#uses=1]

            %conv9 = sext i16 %tmp8 to i32             ; <i32> [#uses=1]

            store i32 %conv9, i32 addrspace(11)* %arrayidx

            ret void

}

 

This function should read from a memory location from input and write to
result with a promotion from i16 to i32, which seems simple enough. The
problem that I am having is somewhere along the line the 16bit load is
being promoted to a 32bit load and then the lower 16 bits are being sign
extended away with a shl 16 followed by a shr 16. 

 

The problem with this is that 

1)       I'm limited to 32bit aligned loads and llvm is assuming a
16bit/8bit alignment

2)       I have special functions that I need to be called when a load
of sub32bit data type occurs which handles the alignment constraints and
then does the shifting and masking of the data

 

So my questions are:

What bits do I need to flip to stop this optimization from occurring?

What do I need to set to correctly get the loads/stores generated if not
setting the datalayout string in my targetmachine class?

 

Thanks,

Micah Villmow

Systems Engineer

Advanced Technology & Performance

Advanced Micro Devices Inc.

S1-609 One AMD Place

Sunnyvale, CA. 94085

P: 408-749-3966

 

 

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