RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2024-11-22 18:54:02 +01:00
Code Issues Projects Releases Wiki Activity
ff0a7ebbd3
llvm-mirror/test/Transforms/InstCombine/bitcast-vec-canon-inseltpoison.ll
Juneyoung Lee a7f581c4d0 [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
2020-12-28 08:58:15 +09:00

168 lines
5.3 KiB
LLVM
Raw Blame History

; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -instcombine -S | FileCheck %s
define double @a(<1 x i64> %y) {
; CHECK-LABEL: @a(
; CHECK-NEXT: [[BC:%.*]] = bitcast <1 x i64> [[Y:%.*]] to <1 x double>
; CHECK-NEXT: [[C:%.*]] = extractelement <1 x double> [[BC]], i32 0
; CHECK-NEXT: ret double [[C]]
;
%c = bitcast <1 x i64> %y to double
ret double %c
}
define i64 @b(<1 x i64> %y) {
; CHECK-LABEL: @b(
; CHECK-NEXT: [[TMP1:%.*]] = extractelement <1 x i64> [[Y:%.*]], i32 0
; CHECK-NEXT: ret i64 [[TMP1]]
;
%c = bitcast <1 x i64> %y to i64
ret i64 %c
}
define <1 x i64> @c(double %y) {
; CHECK-LABEL: @c(
; CHECK-NEXT: [[C:%.*]] = bitcast double [[Y:%.*]] to <1 x i64>
; CHECK-NEXT: ret <1 x i64> [[C]]
;
%c = bitcast double %y to <1 x i64>
ret <1 x i64> %c
}
define <1 x i64> @d(i64 %y) {
; CHECK-LABEL: @d(
; CHECK-NEXT: [[TMP1:%.*]] = insertelement <1 x i64> poison, i64 [[Y:%.*]], i32 0
; CHECK-NEXT: ret <1 x i64> [[TMP1]]
;
%c = bitcast i64 %y to <1 x i64>
ret <1 x i64> %c
}
define x86_mmx @e(<1 x i64> %y) {
; CHECK-LABEL: @e(
; CHECK-NEXT: [[TMP1:%.*]] = extractelement <1 x i64> [[Y:%.*]], i32 0
; CHECK-NEXT: [[C:%.*]] = bitcast i64 [[TMP1]] to x86_mmx
; CHECK-NEXT: ret x86_mmx [[C]]
;
%c = bitcast <1 x i64> %y to x86_mmx
ret x86_mmx %c
}
define <1 x i64> @f(x86_mmx %y) {
; CHECK-LABEL: @f(
; CHECK-NEXT: [[TMP1:%.*]] = bitcast x86_mmx [[Y:%.*]] to i64
; CHECK-NEXT: [[C:%.*]] = insertelement <1 x i64> undef, i64 [[TMP1]], i32 0
; CHECK-NEXT: ret <1 x i64> [[C]]
;
%c = bitcast x86_mmx %y to <1 x i64>
ret <1 x i64> %c
}
define double @g(x86_mmx %x) {
; CHECK-LABEL: @g(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TMP0:%.*]] = bitcast x86_mmx [[X:%.*]] to double
; CHECK-NEXT: ret double [[TMP0]]
;
entry:
%0 = bitcast x86_mmx %x to <1 x i64>
%1 = bitcast <1 x i64> %0 to double
ret double %1
}
; FP source is ok.
define <3 x i64> @bitcast_inselt_undef(double %x, i32 %idx) {
; CHECK-LABEL: @bitcast_inselt_undef(
; CHECK-NEXT: [[TMP1:%.*]] = insertelement <3 x double> undef, double [[X:%.*]], i32 [[IDX:%.*]]
; CHECK-NEXT: [[I:%.*]] = bitcast <3 x double> [[TMP1]] to <3 x i64>
; CHECK-NEXT: ret <3 x i64> [[I]]
;
%xb = bitcast double %x to i64
%i = insertelement <3 x i64> poison, i64 %xb, i32 %idx
ret <3 x i64> %i
}
; Integer source is ok; index is anything.
define <3 x float> @bitcast_inselt_undef_fp(i32 %x, i567 %idx) {
; CHECK-LABEL: @bitcast_inselt_undef_fp(
; CHECK-NEXT: [[TMP1:%.*]] = insertelement <3 x i32> undef, i32 [[X:%.*]], i567 [[IDX:%.*]]
; CHECK-NEXT: [[I:%.*]] = bitcast <3 x i32> [[TMP1]] to <3 x float>
; CHECK-NEXT: ret <3 x float> [[I]]
;
%xb = bitcast i32 %x to float
%i = insertelement <3 x float> poison, float %xb, i567 %idx
ret <3 x float> %i
}
define <vscale x 3 x float> @bitcast_inselt_undef_vscale(i32 %x, i567 %idx) {
; CHECK-LABEL: @bitcast_inselt_undef_vscale(
; CHECK-NEXT: [[TMP1:%.*]] = insertelement <vscale x 3 x i32> undef, i32 [[X:%.*]], i567 [[IDX:%.*]]
; CHECK-NEXT: [[I:%.*]] = bitcast <vscale x 3 x i32> [[TMP1]] to <vscale x 3 x float>
; CHECK-NEXT: ret <vscale x 3 x float> [[I]]
;
%xb = bitcast i32 %x to float
%i = insertelement <vscale x 3 x float> poison, float %xb, i567 %idx
ret <vscale x 3 x float> %i
}
declare void @use(i64)
; Negative test - extra use prevents canonicalization
define <3 x i64> @bitcast_inselt_undef_extra_use(double %x, i32 %idx) {
; CHECK-LABEL: @bitcast_inselt_undef_extra_use(
; CHECK-NEXT: [[XB:%.*]] = bitcast double [[X:%.*]] to i64
; CHECK-NEXT: call void @use(i64 [[XB]])
; CHECK-NEXT: [[I:%.*]] = insertelement <3 x i64> poison, i64 [[XB]], i32 [[IDX:%.*]]
; CHECK-NEXT: ret <3 x i64> [[I]]
;
%xb = bitcast double %x to i64
call void @use(i64 %xb)
%i = insertelement <3 x i64> poison, i64 %xb, i32 %idx
ret <3 x i64> %i
}
; Negative test - source type must be scalar
define <3 x i64> @bitcast_inselt_undef_vec_src(<2 x i32> %x, i32 %idx) {
; CHECK-LABEL: @bitcast_inselt_undef_vec_src(
; CHECK-NEXT: [[XB:%.*]] = bitcast <2 x i32> [[X:%.*]] to i64
; CHECK-NEXT: [[I:%.*]] = insertelement <3 x i64> poison, i64 [[XB]], i32 [[IDX:%.*]]
; CHECK-NEXT: ret <3 x i64> [[I]]
;
%xb = bitcast <2 x i32> %x to i64
%i = insertelement <3 x i64> poison, i64 %xb, i32 %idx
ret <3 x i64> %i
}
; Negative test - source type must be scalar
define <3 x i64> @bitcast_inselt_undef_from_mmx(x86_mmx %x, i32 %idx) {
; CHECK-LABEL: @bitcast_inselt_undef_from_mmx(
; CHECK-NEXT: [[XB:%.*]] = bitcast x86_mmx [[X:%.*]] to i64
; CHECK-NEXT: [[I:%.*]] = insertelement <3 x i64> poison, i64 [[XB]], i32 [[IDX:%.*]]
; CHECK-NEXT: ret <3 x i64> [[I]]
;
%xb = bitcast x86_mmx %x to i64
%i = insertelement <3 x i64> poison, i64 %xb, i32 %idx
ret <3 x i64> %i
}
; Reduce number of casts
define <2 x i64> @PR45748(double %x, double %y) {
; CHECK-LABEL: @PR45748(
; CHECK-NEXT: [[TMP1:%.*]] = insertelement <2 x double> undef, double [[X:%.*]], i32 0
; CHECK-NEXT: [[TMP2:%.*]] = insertelement <2 x double> [[TMP1]], double [[Y:%.*]], i32 1
; CHECK-NEXT: [[I1:%.*]] = bitcast <2 x double> [[TMP2]] to <2 x i64>
; CHECK-NEXT: ret <2 x i64> [[I1]]
;
%xb = bitcast double %x to i64
%i0 = insertelement <2 x i64> poison, i64 %xb, i32 0
%yb = bitcast double %y to i64
%i1 = insertelement <2 x i64> %i0, i64 %yb, i32 1
ret <2 x i64> %i1
}
Reference in New Issue View Git Blame Copy Permalink