llvm/test/Transforms/InstCombine/2012-08-28-udiv_ashl.ll
Nadav Rotem 639570c311 It is illegal to transform (sdiv (ashr X c1) c2) -> (sdiv x (2^c1 * c2)),
because C always rounds towards zero.

Thanks Dirk and Ben.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162899 91177308-0d34-0410-b5e6-96231b3b80d8
2012-08-30 11:23:20 +00:00

58 lines
1.2 KiB
LLVM

; RUN: opt -S -instcombine < %s | FileCheck %s
; rdar://12182093
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.8.0"
; CHECK: @udiv400
; CHECK: udiv i32 %x, 400
; CHECK: ret
define i32 @udiv400(i32 %x) {
entry:
%div = lshr i32 %x, 2
%div1 = udiv i32 %div, 100
ret i32 %div1
}
; CHECK: @udiv400_no
; CHECK: ashr
; CHECK: div
; CHECK: ret
define i32 @udiv400_no(i32 %x) {
entry:
%div = ashr i32 %x, 2
%div1 = udiv i32 %div, 100
ret i32 %div1
}
; CHECK: @sdiv400_yes
; CHECK: udiv i32 %x, 400
; CHECK: ret
define i32 @sdiv400_yes(i32 %x) {
entry:
%div = lshr i32 %x, 2
; The sign bits of both operands are zero (i.e. we can prove they are
; unsigned inputs), turn this into a udiv.
; Next, optimize this just like sdiv.
%div1 = sdiv i32 %div, 100
ret i32 %div1
}
; CHECK: @udiv_i80
; CHECK: udiv i80 %x, 400
; CHECK: ret
define i80 @udiv_i80(i80 %x) {
%div = lshr i80 %x, 2
%div1 = udiv i80 %div, 100
ret i80 %div1
}
define i32 @no_crash_notconst_udiv(i32 %x, i32 %notconst) {
%div = lshr i32 %x, %notconst
%div1 = udiv i32 %div, 100
ret i32 %div1
}