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

[Chris Lattner]

On Jan 12, 2009, at 5:18 PM, Dan Gohman wrote:

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

Absolutely.

-Chris

>
>
> 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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