| ; 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 |
| } |