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Even though we may not know the value of the shifter operand, it's possible we know the shifter operand is non-zero. This can allow us to infer more known bits - for example:
%1 = load %p !range {1, 5}
%2 = shl %q, %1
We don't know %1, but we do know that it is nonzero so %2[0] is known zero, and importantly %2 is known non-zero.
Calling isKnownNonZero is nontrivially expensive so use an Optional to run it lazily and cache its result.
llvm-svn: 251294
14 lines
365 B
LLVM
14 lines
365 B
LLVM
; RUN: opt -instsimplify -S < %s | FileCheck %s
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; CHECK-LABEL: @test
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define i1 @test(i8 %p, i8* %pq) {
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%q = load i8, i8* %pq, !range !0 ; %q is known nonzero; no known bits
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%1 = shl i8 %p, %q ; because %q is nonzero, %1[0] is known to be zero.
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%2 = and i8 %1, 1
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%x = icmp eq i8 %2, 0
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; CHECK: ret i1 true
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ret i1 %x
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}
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!0 = !{ i8 1, i8 5 }
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