fbcf8a8cbb
The constraint system used for ConstraintElimination assumes all varibles to be signed. This can cause missed optimization in the unsigned system, due to missing the information that all variables are unsigned (non-negative). Variables can be marked as non-negative by adding Var >= 0 for all variables. This is done for arguments on ConstraintInfo construction and after adding new variables. This handles cases like the ones outlined in https://discourse.llvm.org/t/why-does-llvm-not-perform-range-analysis-on-integer-values/74341 The original example shared above is now handled without this change, but adding another variable means that instcombine won't be able to simplify examples like https://godbolt.org/z/hTnra7zdY Adding the extra variables comes with a slight compile-time increase https://llvm-compile-time-tracker.com/compare.php?from=7568b36a2bc1a1e496ec29246966ffdfc3a8b87f&to=641a47f0acce7755e340447386013a2e086f03d9&stat=instructions:u stage1-O3 stage1-ReleaseThinLTO stage1-ReleaseLTO-g stage1-O0-g +0.04% +0.07% +0.05% +0.02% stage2-O3 stage2-O0-g stage2-clang +0.05% +0.05% +0.05% https://github.com/llvm/llvm-project/pull/76262
34 lines
1.0 KiB
LLVM
34 lines
1.0 KiB
LLVM
; RUN: opt -passes=constraint-elimination -constraint-elimination-dump-reproducers -pass-remarks=constraint-elimination -debug %s 2>&1 | FileCheck %s
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; REQUIRES: asserts
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target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
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; CHECK: Condition icmp eq ptr %a, null implied by dominating constraints
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; CHECK-NEXT: -1 * %a <= 0
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; CHECK-NEXT: %a <= 0
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; CHECK-NEXT: Creating reproducer for %c.2 = icmp eq ptr %a, null
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; CHECK-NEXT: found external input ptr %a
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; CHECK-NEXT: Materializing assumption icmp eq ptr %a, null
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define i1 @test_ptr_null_constant(ptr %a) {
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; CHECK-LABEL: define i1 @"{{.+}}test_ptr_null_constantrepro"(ptr %a) {
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; CHECK-NEXT: entry:
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; CHECK-NEXT: %0 = icmp eq ptr %a, null
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; CHECK-NEXT: call void @llvm.assume(i1 %0)
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; CHECK-NEXT: %c.2 = icmp eq ptr %a, null
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; CHECK-NEXT: ret i1 %c.2
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; CHECK-NEXT: }
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;
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entry:
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%c.1 = icmp eq ptr %a, null
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br i1 %c.1, label %then, label %else
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then:
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%c.2 = icmp eq ptr %a, null
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ret i1 %c.2
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else:
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ret i1 false
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}
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