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