32 lines
1.3 KiB
LLVM
32 lines
1.3 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt < %s -simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s
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; This is the naive implementation of x86 BZHI/BEXTR instruction:
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; it takes input and bit count, and extracts low nbits up to bit width.
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; I.e. unlike shift it does not have any UB when nbits >= bitwidth.
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; Which means we don't need a while PHI here, simple select will do.
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define i32 @extract_low_bits(i32 %input, i32 %nbits) {
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; CHECK-LABEL: @extract_low_bits(
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; CHECK-NEXT: begin:
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; CHECK-NEXT: [[SHOULD_MASK:%.*]] = icmp ult i32 [[NBITS:%.*]], 32
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; CHECK-NEXT: [[MASK_NOT:%.*]] = shl nsw i32 -1, [[NBITS]]
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; CHECK-NEXT: [[MASK:%.*]] = xor i32 [[MASK_NOT]], -1
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; CHECK-NEXT: [[MASKED:%.*]] = and i32 [[MASK]], [[INPUT:%.*]]
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; CHECK-NEXT: [[RES:%.*]] = select i1 [[SHOULD_MASK]], i32 [[MASKED]], i32 [[INPUT]]
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; CHECK-NEXT: ret i32 [[RES]]
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;
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begin:
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%should_mask = icmp ult i32 %nbits, 32
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br i1 %should_mask, label %perform_masking, label %end
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perform_masking: ; preds = %begin
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%mask.not = shl nsw i32 -1, %nbits
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%mask = xor i32 %mask.not, -1
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%masked = and i32 %mask, %input
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br label %end
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end: ; preds = %perform_masking, %begin
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%res = phi i32 [ %masked, %perform_masking ], [ %input, %begin ]
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ret i32 %res
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}
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