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07aca076e2
Summary: This implements an optimization described in Hacker's Delight 10-17: when `C` is constant, the result of `X % C == 0` can be computed more cheaply without actually calculating the remainder. The motivation is discussed here: https://bugs.llvm.org/show_bug.cgi?id=35479. One huge caveat: this signed case is only valid for positive divisors. While we can freely negate negative divisors, we can't negate `INT_MIN`, so for now if `INT_MIN` is encountered, we bailout. As a follow-up, it should be possible to handle that more gracefully via extra `and`+`setcc`+`select`. This passes llvm's test-suite, and from cursory(!) cross-examination the folds (the assembly) match those of GCC, and manual checking via alive did not reveal any issues (other than the `INT_MIN` case) Reviewers: RKSimon, spatel, hermord, craig.topper, xbolva00 Reviewed By: RKSimon, xbolva00 Subscribers: xbolva00, thakis, javed.absar, hiraditya, dexonsmith, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D65366 llvm-svn: 368702
40 lines
1.2 KiB
LLVM
40 lines
1.2 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
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; RUN: llc -mtriple=aarch64-unknown-linux-gnu < %s | FileCheck %s
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define i32 @test_minsize(i32 %X) optsize minsize nounwind readnone {
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; CHECK-LABEL: test_minsize:
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; CHECK: // %bb.0:
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; CHECK-NEXT: mov w8, #5
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; CHECK-NEXT: sdiv w8, w0, w8
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; CHECK-NEXT: add w8, w8, w8, lsl #2
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; CHECK-NEXT: mov w9, #-10
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; CHECK-NEXT: cmp w0, w8
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; CHECK-NEXT: mov w8, #42
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; CHECK-NEXT: csel w0, w8, w9, eq
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; CHECK-NEXT: ret
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%rem = srem i32 %X, 5
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%cmp = icmp eq i32 %rem, 0
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%ret = select i1 %cmp, i32 42, i32 -10
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ret i32 %ret
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}
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define i32 @test_optsize(i32 %X) optsize nounwind readnone {
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; CHECK-LABEL: test_optsize:
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; CHECK: // %bb.0:
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; CHECK-NEXT: mov w8, #52429
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; CHECK-NEXT: mov w9, #39321
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; CHECK-NEXT: movk w8, #52428, lsl #16
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; CHECK-NEXT: movk w9, #6553, lsl #16
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; CHECK-NEXT: mov w10, #858993459
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; CHECK-NEXT: madd w8, w0, w8, w9
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; CHECK-NEXT: mov w11, #-10
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; CHECK-NEXT: cmp w8, w10
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; CHECK-NEXT: mov w8, #42
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; CHECK-NEXT: csel w0, w8, w11, lo
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; CHECK-NEXT: ret
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%rem = srem i32 %X, 5
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%cmp = icmp eq i32 %rem, 0
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%ret = select i1 %cmp, i32 42, i32 -10
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ret i32 %ret
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}
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