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llvm-mirror/test/CodeGen/X86/shift-i256.ll

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Fix generic shift expansion when shift amount is 0 Summary: This fixes http://llvm.org/bugs/show_bug.cgi?id=16439. This is one possible way to approach this. The other would be to split InL>>(nbits-Amt) into (InL>>(nbits-1-Amt))>>1, which is also valid since since we only need to care about Amt up nbits-1. It's hard to tell which one is better since the shift might be expensive if this stage of expansion is not yet a legal machine integer, whereas comparisons with zero are relatively cheap at all sizes, but more expensive than a shift if the shift is on a legal machine type. Patch by Keno Fischer! Test Plan: regression test from http://reviews.llvm.org/D7752 Reviewers: chfast, resistor Reviewed By: chfast, resistor Subscribers: sanjoy, resistor, chfast, llvm-commits Differential Revision: http://reviews.llvm.org/D4978 llvm-svn: 235370
2015-04-21 08:28:36 +02:00
; RUN: llc < %s -march=x86 | FileCheck %s
; RUN: llc < %s -march=x86-64 -O0 | FileCheck %s -check-prefix=CHECK-X64
; RUN: llc < %s -march=x86-64 -O2 | FileCheck %s -check-prefix=CHECK-X64
Fully general expansion of integer shift of any size. llvm-svn: 68134
2009-03-31 21:39:24 +02:00
Fix generic shift expansion when shift amount is 0 Summary: This fixes http://llvm.org/bugs/show_bug.cgi?id=16439. This is one possible way to approach this. The other would be to split InL>>(nbits-Amt) into (InL>>(nbits-1-Amt))>>1, which is also valid since since we only need to care about Amt up nbits-1. It's hard to tell which one is better since the shift might be expensive if this stage of expansion is not yet a legal machine integer, whereas comparisons with zero are relatively cheap at all sizes, but more expensive than a shift if the shift is on a legal machine type. Patch by Keno Fischer! Test Plan: regression test from http://reviews.llvm.org/D7752 Reviewers: chfast, resistor Reviewed By: chfast, resistor Subscribers: sanjoy, resistor, chfast, llvm-commits Differential Revision: http://reviews.llvm.org/D4978 llvm-svn: 235370
2015-04-21 08:28:36 +02:00
; CHECK-LABEL: shift1
define void @shift1(i256 %x, i256 %a, i256* nocapture %r) nounwind readnone {
Fully general expansion of integer shift of any size. llvm-svn: 68134
2009-03-31 21:39:24 +02:00
entry:
%0 = ashr i256 %x, %a
store i256 %0, i256* %r
ret void
}
Fix generic shift expansion when shift amount is 0 Summary: This fixes http://llvm.org/bugs/show_bug.cgi?id=16439. This is one possible way to approach this. The other would be to split InL>>(nbits-Amt) into (InL>>(nbits-1-Amt))>>1, which is also valid since since we only need to care about Amt up nbits-1. It's hard to tell which one is better since the shift might be expensive if this stage of expansion is not yet a legal machine integer, whereas comparisons with zero are relatively cheap at all sizes, but more expensive than a shift if the shift is on a legal machine type. Patch by Keno Fischer! Test Plan: regression test from http://reviews.llvm.org/D7752 Reviewers: chfast, resistor Reviewed By: chfast, resistor Subscribers: sanjoy, resistor, chfast, llvm-commits Differential Revision: http://reviews.llvm.org/D4978 llvm-svn: 235370
2015-04-21 08:28:36 +02:00
; CHECK-LABEL: shift2
define i256 @shift2(i256 %c) nounwind
{
%b = shl i256 1, %c ; %c must not be a constant
; Special case when %c is 0:
; CHECK-X64: testb [[REG:%r[0-9]+b]], [[REG]]
; CHECK-X64: cmoveq
ret i256 %b
}
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