[InstCombine] Don't treat undef as poison in demanded element simplification

We can only set PoisonElts if the element is poison, not if it is
undef.

Revert "[InstCombine] Favour `m_Poison` in `SimplifyDemandedVectorElts`"

This reverts commit 318d5bff0b65aa7d52fc7004d49587416f0fb564.

Has incomplete test updates.

[InstCombine] Favour `m_Poison` in `SimplifyDemandedVectorElts`

A miscompilation issue has been addressed with refined checking.

[InstCombine] Replace non-demanded undef vector with poison

If an operand (esp to shufflevector or insertelement) is not
demanded, canonicalize it from undef to poison.

[IR] Change shufflevector undef mask to poison

With this patch an undefined mask in a shufflevector will be printed as poison.
This change is done to support the new shufflevector semantics
for unde

[IR] Change shufflevector undef mask to poison

With this patch an undefined mask in a shufflevector will be printed as poison.
This change is done to support the new shufflevector semantics
for undefined mask elements.

Differential Revision: https://reviews.llvm.org/D149210

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[InstCombine] Regenerate all test checks (NFC)

Due to an improvement to name preservation, a lot of InstCombine
tests now show spurious diffs when regenerated.

Rather than regenerating individual f

[InstCombine] Regenerate all test checks (NFC)

Due to an improvement to name preservation, a lot of InstCombine
tests now show spurious diffs when regenerated.

Rather than regenerating individual files when they get touched,
mass-regenerate all UTC-based InstCombine tests. I have then reset
a number of files showing suspicious diffs where the UTC output
has clearly been manually adjusted. I apologize if I missed
anything in the mass of changes.

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[InstCombine] Fold extractelt with select of constants

An extractelt with a constant index which extracts an element from the
two vector operands of a select can be directly folded into a select.

e

[InstCombine] Fold extractelt with select of constants

An extractelt with a constant index which extracts an element from the
two vector operands of a select can be directly folded into a select.

extractelt (select %x, %vec1, %vec2), %const ->
select %x, %vec1[%const], %vec2[%const]

Note: the implementation currently only works for constant vector operands.

Reviewed By: foad, spatel

Differential Revision: https://reviews.llvm.org/D137934

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[test] Use -passes=instcombine instead of -instcombine in lots of tests. NFC

Another step moving away from the deprecated syntax of specifying
pass pipeline in opt.

Differential Revision: https://r

[test] Use -passes=instcombine instead of -instcombine in lots of tests. NFC

Another step moving away from the deprecated syntax of specifying
pass pipeline in opt.

Differential Revision: https://reviews.llvm.org/D119081

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[instcombine] Canonicalize constant index type to i64 for extractelement/insertelement

The basic idea to this is that a) having a single canonical type makes CSE easier, and b) many of our transform

[instcombine] Canonicalize constant index type to i64 for extractelement/insertelement

The basic idea to this is that a) having a single canonical type makes CSE easier, and b) many of our transforms are inconsistent about which types we end up with based on visit order.

I'm restricting this to constants as for non-constants, we'd have to decide whether the simplicity was worth extra instructions. For constants, there are no extra instructions.

We chose the canonical type as i64 arbitrarily. We might consider changing this to something else in the future if we have cause.

Differential Revision: https://reviews.llvm.org/D115387

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[InstCombine] Update InstCombine to use poison instead of undef for shufflevector's placeholder (2/3)

This patch is for fixing potential shufflevector-related bugs like D93818.
As D93818, this patch

[InstCombine] Update InstCombine to use poison instead of undef for shufflevector's placeholder (2/3)

This patch is for fixing potential shufflevector-related bugs like D93818.
As D93818, this patch change shufflevector's default placeholder to poison.
To reduce risk, it was divided into several patches, and this patch is for InstCombineCompares and InstructionCombining.

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D110227

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[InstCombine] use poison as placeholder for undemanded elems

Currently undef is used as a don’t-care vector when constructing a vector using a series of insertelement.
However, this is problematic b

[InstCombine] use poison as placeholder for undemanded elems

Currently undef is used as a don’t-care vector when constructing a vector using a series of insertelement.
However, this is problematic because undef isn’t undefined enough.
Especially, a sequence of insertelement can be optimized to shufflevector, but using undef as its placeholder makes shufflevector a poison-blocking instruction because undef cannot be optimized to poison.
This makes a few straightforward optimizations incorrect, such as:

```
; https://bugs.llvm.org/show_bug.cgi?id=44185

define <4 x float> @insert_not_undef_shuffle_translate_commute(float %x, <4 x float> %y, <4 x float> %q) {
%xv = insertelement <4 x float> %q, float %x, i32 2
%r = shufflevector <4 x float> %y, <4 x float> %xv, <4 x i32> { 0, 6, 2, undef }
ret <4 x float> %r ; %r[3] is undef
}
=>
define <4 x float> @insert_not_undef_shuffle_translate_commute(float %x, <4 x float> %y, <4 x float> %q) {
%r = insertelement <4 x float> %y, float %x, i32 1
ret <4 x float> %r ; %r[3] = %y[3], incorrect if %y[3] = poison
}

Transformation doesn't verify!
ERROR: Target is more poisonous than source
```

I’d like to suggest
1. Using poison as insertelement’s placeholder value (IRBuilder::CreateVectorSplat should be patched too)
2. Updating shufflevector’s semantics to return poison element if mask is undef

Note that poison is currently lowered into UNDEF in SelDag, so codegen part is okay.
m_Undef() matches PoisonValue as well, so existing optimizations will still fire.

The only concern is hidden miscompilations that will go incorrect when poison constant is given.
A conservative way is copying all tests having `insertelement undef` & replacing it with `insertelement poison` & run Alive2 on it, but it will create many tests and people won’t like it. :(

Instead, I’ll simply locally maintain the tests and run Alive2.
If there is any bug found, I’ll report it.

Relevant links: https://bugs.llvm.org/show_bug.cgi?id=43958 , http://lists.llvm.org/pipermail/llvm-dev/2019-November/137242.html

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D93586

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[InstCombine] Fix miscompile bug in canEvaluateShuffled

Summary:
Add restrictions in canEvaluateShuffled to prevent that we for example
transform

%0 = insertelement <2 x i16> undef, i16 %a, i32 0

[InstCombine] Fix miscompile bug in canEvaluateShuffled

Summary:
Add restrictions in canEvaluateShuffled to prevent that we for example
transform

%0 = insertelement <2 x i16> undef, i16 %a, i32 0
%1 = srem <2 x i16> %0, <i16 2, i16 1>
%2 = shufflevector <2 x i16> %1, <2 x i16> undef, <2 x i32> <i32 undef, i32 0>

into

%1 = insertelement <2 x i16> undef, i16 %a, i32 1
%2 = srem <2 x i16> %1, <i16 undef, i16 2>

as having an undef denominator makes the srem undefined (for all
vector elements).

Fixes: https://bugs.llvm.org/show_bug.cgi?id=43689

Reviewers: spatel, lebedev.ri

Reviewed By: spatel, lebedev.ri

Subscribers: lebedev.ri, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69038

llvm-svn: 375208

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[InstCombine] Pre-commit of test case showing miscompile bug in canEvaluateShuffled

Adding the reproducer from https://bugs.llvm.org/show_bug.cgi?id=43689,
showing that instcombine is doing a bad t

[InstCombine] Pre-commit of test case showing miscompile bug in canEvaluateShuffled

Adding the reproducer from https://bugs.llvm.org/show_bug.cgi?id=43689,
showing that instcombine is doing a bad transform. It transforms

%0 = insertelement <2 x i16> undef, i16 %a, i32 0
%1 = srem <2 x i16> %0, <i16 2, i16 1>
%2 = shufflevector <2 x i16> %1, <2 x i16> undef, <2 x i32> <i32 undef, i32 0>

into

%1 = insertelement <2 x i16> undef, i16 %a, i32 1
%2 = srem <2 x i16> %1, <i16 undef, i16 2>

The undef denominator makes the whole srem undefined.

llvm-svn: 375207

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