ad25f8a556
This is a re-commit ofe2c7ee0743which was reverted ina2a58d91e8andea81cea816. This includes a fix to consistently check for EFLAGS being live-out. See phabricator review. Original Summary: This extends `optimizeCompareInstr` to re-use previous comparison results if the previous comparison was with an immediate that was 1 bigger or smaller. Example: CMP x, 13 ... CMP x, 12 ; can be removed if we change the SETg SETg ... ; x > 12 changed to `SETge` (x >= 13) removing CMP Motivation: This often happens because SelectionDAG canonicalization tends to add/subtract 1 often when optimizing for fallthrough blocks. Example for `x > C` the fallthrough optimization switches true/false blocks with `!(x > C)` --> `x <= C` and canonicalization turns this into `x < C + 1`. Differential Revision: https://reviews.llvm.org/D110867
57 lines
1.5 KiB
LLVM
57 lines
1.5 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
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; RUN: llc -o - %s -mtriple=x86_64-- | FileCheck %s
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; Example of a decref operation with "immortal" objects.
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; void decref(long* refcount) {
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; long count = *refcount;
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; if (count == 1) { free_object() }
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; else if (count > 1) { *refcount = count - 1; }
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; else { /* immortal */ }
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; }
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; Resulting assembly should share flags from single CMP instruction for both
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; conditions!
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define void @decref(i32* %p) {
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; CHECK-LABEL: decref:
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; CHECK: # %bb.0:
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; CHECK-NEXT: pushq %rax
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; CHECK-NEXT: .cfi_def_cfa_offset 16
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; CHECK-NEXT: movl (%rdi), %eax
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; CHECK-NEXT: cmpl $1, %eax
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; CHECK-NEXT: jne .LBB0_2
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; CHECK-NEXT: # %bb.1: # %bb_free
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; CHECK-NEXT: callq free_object@PLT
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; CHECK-NEXT: .LBB0_4: # %end
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; CHECK-NEXT: popq %rax
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; CHECK-NEXT: .cfi_def_cfa_offset 8
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; CHECK-NEXT: retq
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; CHECK-NEXT: .LBB0_2: # %bb2
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; CHECK-NEXT: .cfi_def_cfa_offset 16
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; CHECK-NEXT: jle .LBB0_4
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; CHECK-NEXT: # %bb.3: # %bb_dec
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; CHECK-NEXT: decl %eax
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; CHECK-NEXT: movl %eax, (%rdi)
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; CHECK-NEXT: popq %rax
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; CHECK-NEXT: .cfi_def_cfa_offset 8
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; CHECK-NEXT: retq
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%count = load i32, i32* %p, align 4
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%cmp0 = icmp eq i32 %count, 1
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br i1 %cmp0, label %bb_free, label %bb2
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bb2:
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%cmp1 = icmp sgt i32 %count, 1
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br i1 %cmp1, label %bb_dec, label %end
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bb_dec:
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%dec = add nsw i32 %count, -1
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store i32 %dec, i32* %p, align 4
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br label %end
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bb_free:
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call void @free_object()
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br label %end
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end:
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ret void
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}
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declare void @free_object()
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