Trunk Clang fails to build Chromium with "Instruction does not dominate all uses"

[zmodem]

Bugzilla Link	35497
Version	trunk
OS	Linux
Blocks	llvm/llvm-project#30135
CC	@dtemirbulatov,@RKSimon,@rotateright

Extended Description

The regression was introduced somewhere in the 319524:319532 range.

See https://bugs.chromium.org/p/chromium/issues/detail?id=791046#c2 for preprocessed source and invocation.

[rotateright]

There's a lot of debug output spew from SLP, but I don't understand it yet. I've tried to keep the lanes straight by renaming things here. The placement of the unused instruction is important - that seems to be an anchor that causes the misplaced instructions:

define void @​#35497 ([15 x i64] %inptr) { %arrayidx1 = getelementptr [15 x i64], [15 x i64] %inptr, i64 0, i64 0 %arrayidx2 = getelementptr [15 x i64], [15 x i64] %inptr, i64 0, i64 1 %arrayidx3 = getelementptr [15 x i64], [15 x i64] %inptr, i64 0, i64 4 %arrayidx4 = getelementptr [15 x i64], [15 x i64]* %inptr, i64 0, i64 5

%ld1 = load i64, i64 %arrayidx1, align 8 %ld2 = load i64, i64 %arrayidx2, align 8

%a1 = add i64 %ld1, -9 %uu2 = add i64 undef, undef %uu4 = add i64 undef, undef

%unused = add i64 undef, %uu4

%p3 = shl i64 %uu2, 12 %p4 = shl i64 %uu4, 12

%q1 = lshr i64 undef, 16 %q3 = add i64 %p3, 2 %q4 = add i64 %p4, 2

%r1 = add i64 %q1, undef %r2 = add i64 %ld2, 9 %r3 = add i64 undef, %q3 %r4 = add i64 undef, %q4

%s1 = add i64 %a1, %r1 %s2 = add i64 %r2, %uu2 %s3 = add i64 undef, %r3 %s4 = add i64 undef, %r4

store i64 %s1, i64 %arrayidx1, align 8 store i64 %s2, i64 %arrayidx2, align 8 store i64 %s3, i64 %arrayidx3, align 8 store i64 %s4, i64 %arrayidx4, align 8 ret void }

[rotateright]

Bugpoint reduced (too much undef for my taste) IR test:

target triple = "x86_64-unknown-linux-gnu"

define void @​#35497 ([15 x i64] %inptr) { %arrayidx1 = getelementptr inbounds [15 x i64], [15 x i64] %inptr, i64 0, i64 0 %arrayidx2 = getelementptr inbounds [15 x i64], [15 x i64] %inptr, i64 0, i64 1 %t0 = load i64, i64 %arrayidx1, align 8 %t1 = load i64, i64 %arrayidx2, align 8 %add = add i64 %t0, -9223372002495037440 %add.1 = add i64 %t1, 9223372002495037440 %arrayidx3 = getelementptr inbounds [15 x i64], [15 x i64] %inptr, i64 0, i64 4 %arrayidx4 = getelementptr inbounds [15 x i64], [15 x i64] %inptr, i64 0, i64 5 %add24 = add i64 undef, undef %add24.1 = add i64 undef, undef %shr.2 = lshr i64 undef, 16 %add24.2 = add i64 %shr.2, undef %sub12.4 = sub i64 undef, %add24 %and.4 = shl i64 %add24, 12 %shl.4 = and i64 %and.4, 268431360 %add18.4 = add i64 undef, %shl.4 %sub12.5 = sub i64 %add.1, %add24.1 store i64 %sub12.5, i64 %arrayidx2, align 8 %and.5 = shl i64 %add24.1, 12 %shl.5 = and i64 %and.5, 268431360 %add18.5 = add i64 undef, %shl.5 %add24.5 = add i64 undef, %add18.4 store i64 %add24.5, i64 %arrayidx4, align 8 %sub12.6 = sub i64 %add, %add24.2 store i64 %sub12.6, i64 %arrayidx1, align 8 %add24.6 = add i64 undef, %add18.5 store i64 %add24.6, i64* %arrayidx3, align 8 ret void }

[zmodem]

Reverted in r319550

[zmodem]

Reverting the following makes the error go away:

---

r319531 | dinar | 2017-12-01 03:10:47 -0800 (Fri, 01 Dec 2017) | 22 lines

[SLPVectorizer] Failure to beneficially vectorize 'copyable' elements in integer binary ops.

        Patch tries to improve vectorization of the following code:

        void add1(int * __restrict dst, const int * __restrict src) {
          *dst++ = *src++;
          *dst++ = *src++ + 1;
          *dst++ = *src++ + 2;
          *dst++ = *src++ + 3;
        }
        Allows to vectorize even if the very first operation is not a binary add, but just a load.

        Fixed issues related to previous commit.

        Reviewers: spatel, mzolotukhin, mkuper, hfinkel, RKSimon, filcab, ABataev

        Reviewed By: ABataev, RKSimon

        Subscribers: llvm-commits, RKSimon

        Differential Revision: https://reviews.llvm.org/D28907

---

[zmodem]

assigned to @dtemirbulatov