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| author | Sanjay Patel <spatel@rotateright.com> | 2017-06-12 14:23:43 +0000 |
|---|---|---|
| committer | Sanjay Patel <spatel@rotateright.com> | 2017-06-12 14:23:43 +0000 |
| commit | 2e33bbaff0904a8568eac4c9329a39834edf2c68 (patch) | |
| tree | 079dc7754c09115ac2d102f63911871b20118f2f /llvm/test/Transforms/InstCombine/lshr.ll | |
| parent | c0112ae8dacc969b828e7ca17251126413bcc8cc (diff) | |
| download | bcm5719-llvm-2e33bbaff0904a8568eac4c9329a39834edf2c68.tar.gz bcm5719-llvm-2e33bbaff0904a8568eac4c9329a39834edf2c68.zip | |
[InstCombine] lshr (sext iM X to iN), N-M --> zext (ashr X, min(N-M, M-1)) to iN
This is a follow-up to https://reviews.llvm.org/D33879 / https://reviews.llvm.org/rL304939 ,
and was discussed in https://reviews.llvm.org/D33338.
We prefer this form because a narrower shift may be cheaper, and we can more easily fold a
zext than a sext.
http://rise4fun.com/Alive/slVe
Name: shz
%s = sext i8 %x to i12
%r = lshr i12 %s, 4
=>
%a = ashr i8 %x, 4
%r = zext i8 %a to i12
llvm-svn: 305190
Diffstat (limited to 'llvm/test/Transforms/InstCombine/lshr.ll')
| -rw-r--r-- | llvm/test/Transforms/InstCombine/lshr.ll | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/llvm/test/Transforms/InstCombine/lshr.ll b/llvm/test/Transforms/InstCombine/lshr.ll index 71b25177162..4cdcb98f730 100644 --- a/llvm/test/Transforms/InstCombine/lshr.ll +++ b/llvm/test/Transforms/InstCombine/lshr.ll @@ -122,10 +122,19 @@ define <2 x i8> @bool_zext_splat(<2 x i1> %x) { ret <2 x i8> %hibit } -; FIXME: The replicated sign bits are all that's left. This could be ashr+zext. - -define i16 @smear_sign_and_widen(i4 %x) { +define i32 @smear_sign_and_widen(i8 %x) { ; CHECK-LABEL: @smear_sign_and_widen( +; CHECK-NEXT: [[TMP1:%.*]] = ashr i8 %x, 7 +; CHECK-NEXT: [[HIBIT:%.*]] = zext i8 [[TMP1]] to i32 +; CHECK-NEXT: ret i32 [[HIBIT]] +; + %sext = sext i8 %x to i32 + %hibit = lshr i32 %sext, 24 + ret i32 %hibit +} + +define i16 @smear_sign_and_widen_should_not_change_type(i4 %x) { +; CHECK-LABEL: @smear_sign_and_widen_should_not_change_type( ; CHECK-NEXT: [[SEXT:%.*]] = sext i4 %x to i16 ; CHECK-NEXT: [[HIBIT:%.*]] = lshr i16 [[SEXT]], 12 ; CHECK-NEXT: ret i16 [[HIBIT]] @@ -137,8 +146,8 @@ define i16 @smear_sign_and_widen(i4 %x) { define <2 x i8> @smear_sign_and_widen_splat(<2 x i6> %x) { ; CHECK-LABEL: @smear_sign_and_widen_splat( -; CHECK-NEXT: [[SEXT:%.*]] = sext <2 x i6> %x to <2 x i8> -; CHECK-NEXT: [[HIBIT:%.*]] = lshr <2 x i8> [[SEXT]], <i8 2, i8 2> +; CHECK-NEXT: [[TMP1:%.*]] = ashr <2 x i6> %x, <i6 2, i6 2> +; CHECK-NEXT: [[HIBIT:%.*]] = zext <2 x i6> [[TMP1]] to <2 x i8> ; CHECK-NEXT: ret <2 x i8> [[HIBIT]] ; %sext = sext <2 x i6> %x to <2 x i8> |
