ed3f06b9b3
Add an nneg flag to the zext instruction, which specifies that the argument is non-negative. Otherwise, the result is a poison value. The primary use-case for the flag is to preserve information when sext gets replaced with zext due to range-based canonicalization. The nneg flag allows us to convert the zext back into an sext later. This is useful for some optimizations (e.g. a signed icmp can fold with sext but not zext), as well as some targets (e.g. RISCV prefers sext over zext). Discourse thread: https://discourse.llvm.org/t/rfc-add-zext-nneg-flag/73914 This patch is based on https://reviews.llvm.org/D156444 by @Panagiotis156, with some implementation simplifications and additional tests. --------- Co-authored-by: Panagiotis K <karouzakispan@gmail.com>
33 lines
1.2 KiB
LLVM
33 lines
1.2 KiB
LLVM
; RUN: llvm-as < %s | llvm-dis > %t0
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; RUN: opt -S < %s > %t1
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; RUN: diff %t0 %t1
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; RUN: verify-uselistorder < %s
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; PR6140
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; Make sure the flags are serialized/deserialized properly for both
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; forward and backward references.
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define void @foo() nounwind {
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entry:
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br label %first
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second: ; preds = %first
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%u = add nuw i32 %a, 0 ; <i32> [#uses=0]
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%s = add nsw i32 %a, 0 ; <i32> [#uses=0]
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%us = add nuw nsw i32 %a, 0 ; <i32> [#uses=0]
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%z = add i32 %a, 0 ; <i32> [#uses=0]
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%hh = zext nneg i32 %a to i64
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%ll = zext i32 %s to i64
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unreachable
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first: ; preds = %entry
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%a = bitcast i32 0 to i32 ; <i32> [#uses=8]
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%uu = add nuw i32 %a, 0 ; <i32> [#uses=0]
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%ss = add nsw i32 %a, 0 ; <i32> [#uses=0]
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%uuss = add nuw nsw i32 %a, 0 ; <i32> [#uses=0]
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%zz = add i32 %a, 0 ; <i32> [#uses=0]
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%kk = zext nneg i32 %a to i64
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%rr = zext i32 %ss to i64
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br label %second
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}
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