90ba33099c
This patch canonicalizes getelementptr instructions with constant indices to use the `i8` source element type. This makes it easier for optimizations to recognize that two GEPs are identical, because they don't need to see past many different ways to express the same offset. This is a first step towards https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699. This is limited to constant GEPs only for now, as they have a clear canonical form, while we're not yet sure how exactly to deal with variable indices. The test llvm/test/Transforms/PhaseOrdering/switch_with_geps.ll gives two representative examples of the kind of optimization improvement we expect from this change. In the first test SimplifyCFG can now realize that all switch branches are actually the same. In the second test it can convert it into simple arithmetic. These are representative of common optimization failures we see in Rust. Fixes https://github.com/llvm/llvm-project/issues/69841.
48 lines
1.8 KiB
LLVM
48 lines
1.8 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt < %s -passes=instcombine -S 2>&1 | FileCheck %s
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target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
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; We are really checking that this doesn't loop forever. We would never
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; actually get to the checks here if it did.
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define void @timeout(ptr nocapture readonly %cinfo, ptr %ptr) {
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; CHECK-LABEL: @timeout(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br label [[FOR_BODY:%.*]]
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; CHECK: for.body:
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; CHECK-NEXT: [[ARRAYIDX15:%.*]] = getelementptr inbounds i8, ptr [[CINFO:%.*]], i32 4
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; CHECK-NEXT: [[L:%.*]] = load i16, ptr [[ARRAYIDX15]], align 2
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; CHECK-NEXT: [[CMP17:%.*]] = icmp eq i16 [[L]], 0
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; CHECK-NEXT: [[EXTRACT_T1:%.*]] = trunc i16 [[L]] to i8
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; CHECK-NEXT: br i1 [[CMP17]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
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; CHECK: if.then:
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; CHECK-NEXT: [[DOTPRE:%.*]] = load i16, ptr [[ARRAYIDX15]], align 2
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; CHECK-NEXT: [[EXTRACT_T:%.*]] = trunc i16 [[DOTPRE]] to i8
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; CHECK-NEXT: br label [[IF_END]]
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; CHECK: if.end:
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; CHECK-NEXT: [[P_OFF0:%.*]] = phi i8 [ [[EXTRACT_T]], [[IF_THEN]] ], [ [[EXTRACT_T1]], [[FOR_BODY]] ]
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; CHECK-NEXT: [[SUB:%.*]] = add i8 [[P_OFF0]], -1
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; CHECK-NEXT: store i8 [[SUB]], ptr [[PTR:%.*]], align 1
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; CHECK-NEXT: br label [[FOR_BODY]]
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;
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entry:
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br label %for.body
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for.body:
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%arrayidx15 = getelementptr inbounds i16, ptr %cinfo, i32 2
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%l = load i16, ptr %arrayidx15, align 2
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%cmp17 = icmp eq i16 %l, 0
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br i1 %cmp17, label %if.then, label %if.end
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if.then:
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%.pre = load i16, ptr %arrayidx15, align 2
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br label %if.end
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if.end:
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%p = phi i16 [ %.pre, %if.then ], [ %l, %for.body ]
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%conv19 = trunc i16 %p to i8
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%sub = add i8 %conv19, -1
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store i8 %sub, ptr %ptr, align 1
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br label %for.body
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}
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