https://llvm.org/bugs/show_bug.cgi?id=26024
Bug ID: 26024
Summary: [AArch64] Regression introduced by r255388 (match
min/max if the scalar operation is legal)
Product: tools
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: llc
Assignee: unassignedb...@nondot.org
Reporter: apa...@codeaurora.org
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Hi Matt,
I came across a failure on AArch64 that seems to have been introduced with
commit r255388 - SelectionDAG: Match min/max if the scalar operation is legal.
Here is a reduced test case:
; RUN: llc < %s -mtriple=aarch64-linux-gnu | FileCheck %s
define i8 @test(<4 x i8> %a) {
%low = shufflevector <4 x i8> %a, <4 x i8> undef, <2 x i32> <i32 0, i32 1>
%high = shufflevector <4 x i8> %a, <4 x i8> undef, <2 x i32> <i32 2, i32 3>
%1 = icmp sgt <2 x i8> %low, %high
%2 = select <2 x i1> %1, <2 x i8> %low, <2 x i8> %high
%3 = extractelement <2 x i8> %2, i32 0
ret i8 %3
}
Before your patch, we see the code to extract the byte values from the promoted
vectors before comparing the vectors:
// BB#0:
umov w8, v0.h[0]
umov w9, v0.h[2]
fmov s1, w8
fmov s2, w9
umov w8, v0.h[1]
ins v1.s[1], w8
umov w8, v0.h[3]
ins v2.s[1], w8
shl v0.2s, v1.2s, #24
shl v3.2s, v2.2s, #24
sshr v0.2s, v0.2s, #24
sshr v3.2s, v3.2s, #24
cmgt v0.2s, v0.2s, v3.2s
bsl v0.8b, v1.8b, v2.8b
fmov w0, s0
ret
With your patch, smax is generated directly based on the promoted vector type:
// BB#0:
umov w8, v0.h[0]
umov w9, v0.h[1]
umov w10, v0.h[2]
umov w11, v0.h[3]
fmov s0, w8
fmov s1, w10
ins v0.s[1], w9
ins v1.s[1], w11
smax v0.2s, v0.2s, v1.2s
fmov w0, s0
ret
This is causing some benchmark miscompares in my AArhc64 workloads.
Can you take a look please?
--
You are receiving this mail because:
You are on the CC list for the bug.
_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
