[llvm-commits] [llvm] r44981 - in /llvm/trunk: lib/Transforms/Scalar/CodeGenPrepare.cpp test/CodeGen/X86/opt-ext-uses.ll

[Chris Lattner]

On Dec 12, 2007, at 7:32 PM, Evan Cheng wrote:

> Author: evancheng
> Date: Wed Dec 12 21:32:53 2007
> New Revision: 44981
>
> URL: http://llvm.org/viewvc/llvm-project?rev=44981&view=rev
> Log:
> Be extra careful with extension use optimation. Now turned on by  
> default.

FYI, on your testcase with -print-isel-input, it looks like multiple  
instructions are sunk:


cond_true188:		; preds = %entry
	trunc i32 %tmp180181 to i16		; <i16>:0 [#uses=1]
	trunc i32 %tmp180181 to i16		; <i16>:1 [#uses=1]
	%tmp195196 = trunc i16 %0 to i8		; <i8> [#uses=0]
	ret i16 %1

Is this desired?

-Chris

>
>
> Modified:
>    llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp
>    llvm/trunk/test/CodeGen/X86/opt-ext-uses.ll
>
> Modified: llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp?rev=44981&r1=44980&r2=44981&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp Wed Dec 12  
> 21:32:53 2007
> @@ -36,7 +36,7 @@
>
> namespace {
>   cl::opt<bool> OptExtUses("optimize-ext-uses",
> -                           cl::init(false), cl::Hidden);
> +                           cl::init(true), cl::Hidden);
> }
>
> namespace {
> @@ -929,6 +929,10 @@
>   if (Src->hasOneUse())
>     return false;
>
> +  // Only do this xform is truncating is free.
> +  if (!TLI->isTruncateFree(I->getType(), Src->getType()))
> +    return false;
> +
>   // Only safe to perform the optimization if the source is also  
> defined in
>   // this block.
>   if (!isa<Instruction>(Src) || DefBB != cast<Instruction>(Src)- 
> >getParent())
> @@ -952,8 +956,11 @@
>   for (Value::use_iterator UI = Src->use_begin(), E = Src->use_end();
>        UI != E; ++UI) {
>     Instruction *User = cast<Instruction>(*UI);
> -    if (User->getParent() == DefBB) continue;
> -    if (isa<PHINode>(User))
> +    BasicBlock *UserBB = User->getParent();
> +    if (UserBB == DefBB) continue;
> +    // Be conservative. We don't want this xform to end up  
> introducing
> +    // reloads just before load / store instructions.
> +    if (isa<PHINode>(User) || isa<LoadInst>(User) ||  
> isa<StoreInst>(User))
>       return false;
>   }
>
>
> Modified: llvm/trunk/test/CodeGen/X86/opt-ext-uses.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/opt-ext-uses.ll?rev=44981&r1=44980&r2=44981&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/test/CodeGen/X86/opt-ext-uses.ll (original)
> +++ llvm/trunk/test/CodeGen/X86/opt-ext-uses.ll Wed Dec 12 21:32:53  
> 2007
> @@ -1,4 +1,4 @@
> -; RUN: llvm-as < %s | llc -march=x86 -optimize-ext-uses=true | grep  
> movw | count 1
> +; RUN: llvm-as < %s | llc -march=x86 | grep movw | count 1
>
> define i16 @t() signext  {
> entry:
>
>
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