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llvm-mirror/test/Transforms/InstCombine/shift-amount-reassociation-with-truncation-lshr.ll
Roman Lebedev 5dbe65e8a0 [NFC][InstCombine] More test for "sign bit test via shifts" pattern (PR43595) 
While that pattern is indirectly handled via
reassociateShiftAmtsOfTwoSameDirectionShifts(),
that incursme one-use restriction on truncation,
which is pointless since we know that we'll produce a single instruction.

Additionally, *if* we are only looking for sign bit,
we don't need shifts to be identical,
which isn't the case in general,
and is the blocker for me in bug in question:

https://bugs.llvm.org/show_bug.cgi?id=43595

llvm-svn: 374726
2019-10-13 17:11:16 +00:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt %s -instcombine -S | FileCheck %s
; Given pattern:
; (trunc (iSrc x l>> Q) to iDst) l>> K
; we should rewrite it as
; (trunc (iSrc x l>> (Q+K)) to iDst)
; iff (Q+K) is bitwidth(iSrc)-1
; THIS FOLD DOES *NOT* REQUIRE ANY 'nuw'/`nsw` FLAGS!
; Basic scalar test
define i16 @t0(i32 %x, i16 %y) {
; CHECK-LABEL: @t0(
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 31
; CHECK-NEXT: [[T5:%.*]] = trunc i32 [[TMP1]] to i16
; CHECK-NEXT: ret i16 [[T5]]
;
%t0 = sub i16 32, %y
%t1 = zext i16 %t0 to i32
%t2 = lshr i32 %x, %t1
%t3 = trunc i32 %t2 to i16
%t4 = add i16 %y, -1
%t5 = lshr i16 %t3, %t4
ret i16 %t5
}
; Basic vector tests
define <2 x i16> @t1_vec_splat(<2 x i32> %x, <2 x i16> %y) {
; CHECK-LABEL: @t1_vec_splat(
; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> [[X:%.*]], <i32 31, i32 31>
; CHECK-NEXT: [[T5:%.*]] = trunc <2 x i32> [[TMP1]] to <2 x i16>
; CHECK-NEXT: ret <2 x i16> [[T5]]
;
%t0 = sub <2 x i16> <i16 32, i16 32>, %y
%t1 = zext <2 x i16> %t0 to <2 x i32>
%t2 = lshr <2 x i32> %x, %t1
%t3 = trunc <2 x i32> %t2 to <2 x i16>
%t4 = add <2 x i16> %y, <i16 -1, i16 -1>
%t5 = lshr <2 x i16> %t3, %t4
ret <2 x i16> %t5
}
define <3 x i16> @t3_vec_nonsplat_undef0(<3 x i32> %x, <3 x i16> %y) {
; CHECK-LABEL: @t3_vec_nonsplat_undef0(
; CHECK-NEXT: [[TMP1:%.*]] = lshr <3 x i32> [[X:%.*]], <i32 31, i32 0, i32 31>
; CHECK-NEXT: [[T5:%.*]] = trunc <3 x i32> [[TMP1]] to <3 x i16>
; CHECK-NEXT: ret <3 x i16> [[T5]]
;
%t0 = sub <3 x i16> <i16 32, i16 undef, i16 32>, %y
%t1 = zext <3 x i16> %t0 to <3 x i32>
%t2 = lshr <3 x i32> %x, %t1
%t3 = trunc <3 x i32> %t2 to <3 x i16>
%t4 = add <3 x i16> %y, <i16 -1, i16 -1, i16 -1>
%t5 = lshr <3 x i16> %t3, %t4
ret <3 x i16> %t5
}
define <3 x i16> @t4_vec_nonsplat_undef1(<3 x i32> %x, <3 x i16> %y) {
; CHECK-LABEL: @t4_vec_nonsplat_undef1(
; CHECK-NEXT: [[TMP1:%.*]] = lshr <3 x i32> [[X:%.*]], <i32 31, i32 0, i32 31>
; CHECK-NEXT: [[T5:%.*]] = trunc <3 x i32> [[TMP1]] to <3 x i16>
; CHECK-NEXT: ret <3 x i16> [[T5]]
;
%t0 = sub <3 x i16> <i16 32, i16 32, i16 32>, %y
%t1 = zext <3 x i16> %t0 to <3 x i32>
%t2 = lshr <3 x i32> %x, %t1
%t3 = trunc <3 x i32> %t2 to <3 x i16>
%t4 = add <3 x i16> %y, <i16 -1, i16 undef, i16 -1>
%t5 = lshr <3 x i16> %t3, %t4
ret <3 x i16> %t5
}
define <3 x i16> @t5_vec_nonsplat_undef1(<3 x i32> %x, <3 x i16> %y) {
; CHECK-LABEL: @t5_vec_nonsplat_undef1(
; CHECK-NEXT: [[TMP1:%.*]] = lshr <3 x i32> [[X:%.*]], <i32 31, i32 0, i32 31>
; CHECK-NEXT: [[T5:%.*]] = trunc <3 x i32> [[TMP1]] to <3 x i16>
; CHECK-NEXT: ret <3 x i16> [[T5]]
;
%t0 = sub <3 x i16> <i16 32, i16 undef, i16 32>, %y
%t1 = zext <3 x i16> %t0 to <3 x i32>
%t2 = lshr <3 x i32> %x, %t1
%t3 = trunc <3 x i32> %t2 to <3 x i16>
%t4 = add <3 x i16> %y, <i16 -1, i16 undef, i16 -1>
%t5 = lshr <3 x i16> %t3, %t4
ret <3 x i16> %t5
}
; One-use tests
declare void @use16(i16)
declare void @use32(i32)
define i16 @t6_extrause0(i32 %x, i16 %y) {
; CHECK-LABEL: @t6_extrause0(
; CHECK-NEXT: [[T0:%.*]] = sub i16 32, [[Y:%.*]]
; CHECK-NEXT: [[T1:%.*]] = zext i16 [[T0]] to i32
; CHECK-NEXT: [[T2:%.*]] = lshr i32 [[X:%.*]], [[T1]]
; CHECK-NEXT: [[T3:%.*]] = trunc i32 [[T2]] to i16
; CHECK-NEXT: call void @use16(i16 [[T3]])
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X]], 31
; CHECK-NEXT: [[T5:%.*]] = trunc i32 [[TMP1]] to i16
; CHECK-NEXT: ret i16 [[T5]]
;
%t0 = sub i16 32, %y
%t1 = zext i16 %t0 to i32
%t2 = lshr i32 %x, %t1
%t3 = trunc i32 %t2 to i16
%t4 = add i16 %y, -1
call void @use16(i16 %t3)
%t5 = lshr i16 %t3, %t4
ret i16 %t5
}
define i16 @t7_extrause1(i32 %x, i16 %y) {
; CHECK-LABEL: @t7_extrause1(
; CHECK-NEXT: [[T4:%.*]] = add i16 [[Y:%.*]], -1
; CHECK-NEXT: call void @use16(i16 [[T4]])
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 31
; CHECK-NEXT: [[T5:%.*]] = trunc i32 [[TMP1]] to i16
; CHECK-NEXT: ret i16 [[T5]]
;
%t0 = sub i16 32, %y
%t1 = zext i16 %t0 to i32
%t2 = lshr i32 %x, %t1
%t3 = trunc i32 %t2 to i16
%t4 = add i16 %y, -1
call void @use16(i16 %t4)
%t5 = lshr i16 %t3, %t4
ret i16 %t5
}
define i16 @t8_extrause2(i32 %x, i16 %y) {
; CHECK-LABEL: @t8_extrause2(
; CHECK-NEXT: [[T0:%.*]] = sub i16 32, [[Y:%.*]]
; CHECK-NEXT: [[T1:%.*]] = zext i16 [[T0]] to i32
; CHECK-NEXT: [[T2:%.*]] = lshr i32 [[X:%.*]], [[T1]]
; CHECK-NEXT: [[T3:%.*]] = trunc i32 [[T2]] to i16
; CHECK-NEXT: [[T4:%.*]] = add i16 [[Y]], -1
; CHECK-NEXT: call void @use16(i16 [[T3]])
; CHECK-NEXT: call void @use16(i16 [[T4]])
; CHECK-NEXT: [[T5:%.*]] = lshr i16 [[T3]], [[T4]]
; CHECK-NEXT: ret i16 [[T5]]
;
%t0 = sub i16 32, %y
%t1 = zext i16 %t0 to i32
%t2 = lshr i32 %x, %t1
%t3 = trunc i32 %t2 to i16
%t4 = add i16 %y, -1
call void @use16(i16 %t3)
call void @use16(i16 %t4)
%t5 = lshr i16 %t3, %t4
ret i16 %t5
}
; No 'nuw'/'nsw' flags are to be propagated!
; But we can't test that, such IR does not reach that code.
; Negative tests
; Can only fold if we are extracting the sign bit.
define i16 @t9_lshr(i32 %x, i16 %y) {
; CHECK-LABEL: @t9_lshr(
; CHECK-NEXT: [[T0:%.*]] = sub i16 32, [[Y:%.*]]
; CHECK-NEXT: [[T1:%.*]] = zext i16 [[T0]] to i32
; CHECK-NEXT: [[T2:%.*]] = lshr i32 [[X:%.*]], [[T1]]
; CHECK-NEXT: [[T3:%.*]] = trunc i32 [[T2]] to i16
; CHECK-NEXT: [[T4:%.*]] = add i16 [[Y]], -2
; CHECK-NEXT: [[T5:%.*]] = lshr i16 [[T3]], [[T4]]
; CHECK-NEXT: ret i16 [[T5]]
;
%t0 = sub i16 32, %y
%t1 = zext i16 %t0 to i32
%t2 = lshr i32 %x, %t1
%t3 = trunc i32 %t2 to i16
%t4 = add i16 %y, -2
%t5 = lshr i16 %t3, %t4
ret i16 %t5
}
; If we have different right-shifts, in general, we can't do anything with it.
define i16 @n10_ashr_lshr(i32 %x, i16 %y) {
; CHECK-LABEL: @n10_ashr_lshr(
; CHECK-NEXT: [[T0:%.*]] = sub i16 32, [[Y:%.*]]
; CHECK-NEXT: [[T1:%.*]] = zext i16 [[T0]] to i32
; CHECK-NEXT: [[T2:%.*]] = ashr i32 [[X:%.*]], [[T1]]
; CHECK-NEXT: [[T3:%.*]] = trunc i32 [[T2]] to i16
; CHECK-NEXT: [[T4:%.*]] = add i16 [[Y]], -1
; CHECK-NEXT: [[T5:%.*]] = lshr i16 [[T3]], [[T4]]
; CHECK-NEXT: ret i16 [[T5]]
;
%t0 = sub i16 32, %y
%t1 = zext i16 %t0 to i32
%t2 = ashr i32 %x, %t1
%t3 = trunc i32 %t2 to i16
%t4 = add i16 %y, -1
%t5 = lshr i16 %t3, %t4
ret i16 %t5
}
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