[llvm-commits] [llvm] r61985 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/cast.ll test/Transforms/InstCombine/icmp.ll

[Dan Gohman]

Hi Chris,

The recent 176.gcc JIT regression on darwin x86-32 isolated down to
this commit. Can you investigate?

Thanks,

Dan

On Jan 8, 2009, at 11:47 PM, Chris Lattner wrote:

> Author: lattner
> Date: Fri Jan  9 01:47:06 2009
> New Revision: 61985
>
> URL: http://llvm.org/viewvc/llvm-project?rev=61985&view=rev
> Log:
> Implement rdar://6480391, extending of equality icmp's to avoid a  
> truncation.
> I noticed this in the code compiled for a routine using std::map,  
> which produced
> this code:
> 	%25 = tail call i32 @memcmp(i8* %24, i8* %23, i32 6) nounwind  
> readonly
> 	%.lobit.i = lshr i32 %25, 31		; <i32> [#uses=1]
> 	%tmp.i = trunc i32 %.lobit.i to i8		; <i8> [#uses=1]
> 	%toBool = icmp eq i8 %tmp.i, 0		; <i1> [#uses=1]
> 	br i1 %toBool, label %bb3, label %bb4
> which compiled to:
>
> 	call	L_memcmp$stub
> 	shrl	$31, %eax
> 	testb	%al, %al
> 	jne	LBB1_11	##
>
> with this change, we compile it to:
>
> 	call	L_memcmp$stub
> 	testl	%eax, %eax
> 	js	LBB1_11
>
> This triggers all the time in common code, with patters like this:
>
> 	%169 = and i32 %ply, 1		; <i32> [#uses=1]
> 	%170 = trunc i32 %169 to i8		; <i8> [#uses=1]
> 	%toBool = icmp ne i8 %170, 0		; <i1> [#uses=1]
>
> 	%7 = lshr i32 %6, 24		; <i32> [#uses=1]
> 	%9 = trunc i32 %7 to i8		; <i8> [#uses=1]
> 	%10 = icmp ne i8 %9, 0		; <i1> [#uses=1]
>
> etc
>
>
> Modified:
>    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
>    llvm/trunk/test/Transforms/InstCombine/cast.ll
>    llvm/trunk/test/Transforms/InstCombine/icmp.ll
>
> Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=61985&r1=61984&r2=61985&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp  
> (original)
> +++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Fri  
> Jan  9 01:47:06 2009
> @@ -6343,6 +6343,28 @@
>   const APInt &RHSV = RHS->getValue();
>
>   switch (LHSI->getOpcode()) {
> +  case Instruction::Trunc:
> +    if (ICI.isEquality() && LHSI->hasOneUse()) {
> +      // Simplify icmp eq (trunc x to i8), 42 -> icmp eq x, 42| 
> highbits if all
> +      // of the high bits truncated out of x are known.
> +      unsigned DstBits = LHSI->getType()->getPrimitiveSizeInBits(),
> +             SrcBits = LHSI->getOperand(0)->getType()- 
> >getPrimitiveSizeInBits();
> +      APInt Mask(APInt::getHighBitsSet(SrcBits, SrcBits-DstBits));
> +      APInt KnownZero(SrcBits, 0), KnownOne(SrcBits, 0);
> +      ComputeMaskedBits(LHSI->getOperand(0), Mask, KnownZero,  
> KnownOne);
> +
> +      // If all the high bits are known, we can do this xform.
> +      if ((KnownZero|KnownOne).countLeadingOnes() >= SrcBits- 
> DstBits) {
> +        // Pull in the high bits from known-ones set.
> +        APInt NewRHS(RHS->getValue());
> +        NewRHS.zext(SrcBits);
> +        NewRHS |= KnownOne;
> +        return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0),
> +                            ConstantInt::get(NewRHS));
> +      }
> +    }
> +    break;
> +
>   case Instruction::Xor:         // (icmp pred (xor X, XorCST), CI)
>     if (ConstantInt *XorCST = dyn_cast<ConstantInt>(LHSI- 
> >getOperand(1))) {
>       // If this is a comparison that tests the signbit (X < 0) or  
> (x > -1),
>
> Modified: llvm/trunk/test/Transforms/InstCombine/cast.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/cast.ll?rev=61985&r1=61984&r2=61985&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/test/Transforms/InstCombine/cast.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/cast.ll Fri Jan  9  
> 01:47:06 2009
> @@ -1,7 +1,5 @@
> ; Tests to make sure elimination of casts is working correctly
> -; RUN: llvm-as < %s | opt -instcombine | llvm-dis | \
> -; RUN:    grep %c | notcast
> -; END.
> +; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep %c | notcast
>
> @inbuf = external global [32832 x i8]           ; <[32832 x i8]*>  
> [#uses=1]
>
> @@ -238,3 +236,21 @@
>         ret i16 %c2
> }
>
> +; icmp sgt i32 %a, -1
> +; rdar://6480391
> +define i1 @test36(i32 %a) {
> +        %b = lshr i32 %a, 31
> +        %c = trunc i32 %b to i8
> +        %d = icmp eq i8 %c, 0
> +        ret i1 %d
> +}
> +
> +; ret i1 false
> +define i1 @test37(i32 %a) {
> +        %b = lshr i32 %a, 31
> +        %c = or i32 %b, 512
> +        %d = trunc i32 %c to i8
> +        %e = icmp eq i8 %d, 11
> +        ret i1 %e
> +}
> +
>
> Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=61985&r1=61984&r2=61985&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Fri Jan  9  
> 01:47:06 2009
> @@ -1,5 +1,4 @@
> ; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep icmp
> -; END.
>
> define i32 @test1(i32 %X) {
> entry:
>
>
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