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bccf832eec
Summary: Related to https://bugs.llvm.org/show_bug.cgi?id=37793, https://reviews.llvm.org/D46760#1127287 We'd like to do this canonicalization https://rise4fun.com/Alive/Gmc But it is currently restricted by rL155136 / rL155362, which says: ``` // This is a constant shift of a constant shift. Be careful about hiding // shl instructions behind bit masks. They are used to represent multiplies // by a constant, and it is important that simple arithmetic expressions // are still recognizable by scalar evolution. // // The transforms applied to shl are very similar to the transforms applied // to mul by constant. We can be more aggressive about optimizing right // shifts. // // Combinations of right and left shifts will still be optimized in // DAGCombine where scalar evolution no longer applies. ``` I think these tests show that for *constants*, SCEV has no issues with that canonicalization. Reviewers: mkazantsev, spatel, efriedma, sanjoy Reviewed By: mkazantsev Subscribers: sanjoy, javed.absar, llvm-commits, stoklund, bixia Differential Revision: https://reviews.llvm.org/D48229 llvm-svn: 335101
49 lines
1.7 KiB
LLVM
49 lines
1.7 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
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; RUN: opt -S -analyze -scalar-evolution < %s | FileCheck %s
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; The obvious case.
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define i32 @mul(i32 %val) nounwind {
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; CHECK-LABEL: 'mul'
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; CHECK-NEXT: Classifying expressions for: @mul
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; CHECK-NEXT: %tmp1 = mul i32 %val, 16
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; CHECK-NEXT: --> (16 * %val) U: [0,-15) S: [-2147483648,2147483633)
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; CHECK-NEXT: %tmp2 = udiv i32 %tmp1, 16
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; CHECK-NEXT: --> ((16 * %val) /u 16) U: [0,268435456) S: [0,268435456)
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; CHECK-NEXT: Determining loop execution counts for: @mul
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;
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%tmp1 = mul i32 %val, 16
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%tmp2 = udiv i32 %tmp1, 16
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ret i32 %tmp2
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}
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; Or, it could be any number of equivalent patterns with mask:
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; a) x & (1 << nbits) - 1
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; b) x & ~(-1 << nbits)
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; c) x & (-1 >> (32 - y))
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; d) x << (32 - y) >> (32 - y)
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define i32 @mask_abc(i32 %val) nounwind {
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; CHECK-LABEL: 'mask_abc'
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; CHECK-NEXT: Classifying expressions for: @mask_abc
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; CHECK-NEXT: %masked = and i32 %val, 15
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; CHECK-NEXT: --> (zext i4 (trunc i32 %val to i4) to i32) U: [0,16) S: [0,16)
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; CHECK-NEXT: Determining loop execution counts for: @mask_abc
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;
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%masked = and i32 %val, 15
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ret i32 %masked
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}
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define i32 @mask_d(i32 %val) nounwind {
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; CHECK-LABEL: 'mask_d'
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; CHECK-NEXT: Classifying expressions for: @mask_d
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; CHECK-NEXT: %highbitscleared = shl i32 %val, 4
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; CHECK-NEXT: --> (16 * %val) U: [0,-15) S: [-2147483648,2147483633)
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; CHECK-NEXT: %masked = lshr i32 %highbitscleared, 4
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; CHECK-NEXT: --> ((16 * %val) /u 16) U: [0,268435456) S: [0,268435456)
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; CHECK-NEXT: Determining loop execution counts for: @mask_d
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;
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%highbitscleared = shl i32 %val, 4
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%masked = lshr i32 %highbitscleared, 4
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ret i32 %masked
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}
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