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This change, which allows @llvm.assume to be used from within computeKnownBits (and other associated functions in ValueTracking), adds some (optional) parameters to computeKnownBits and friends. These functions now (optionally) take a "context" instruction pointer, an AssumptionTracker pointer, and also a DomTree pointer, and most of the changes are just to pass this new information when it is easily available from InstSimplify, InstCombine, etc. As explained below, the significant conceptual change is that known properties of a value might depend on the control-flow location of the use (because we care that the @llvm.assume dominates the use because assumptions have control-flow dependencies). This means that, when we ask if bits are known in a value, we might get different answers for different uses. The significant changes are all in ValueTracking. Two main changes: First, as with the rest of the code, new parameters need to be passed around. To make this easier, I grouped them into a structure, and I made internal static versions of the relevant functions that take this structure as a parameter. The new code does as you might expect, it looks for @llvm.assume calls that make use of the value we're trying to learn something about (often indirectly), attempts to pattern match that expression, and uses the result if successful. By making use of the AssumptionTracker, the process of finding @llvm.assume calls is not expensive. Part of the structure being passed around inside ValueTracking is a set of already-considered @llvm.assume calls. This is to prevent a query using, for example, the assume(a == b), to recurse on itself. The context and DT params are used to find applicable assumptions. An assumption needs to dominate the context instruction, or come after it deterministically. In this latter case we only handle the specific case where both the assumption and the context instruction are in the same block, and we need to exclude assumptions from being used to simplify their own ephemeral values (those which contribute only to the assumption) because otherwise the assumption would prove its feeding comparison trivial and would be removed. This commit adds the plumbing and the logic for a simple masked-bit propagation (just enough to write a regression test). Future commits add more patterns (and, correspondingly, more regression tests). llvm-svn: 217342
48 lines
1.5 KiB
LLVM
48 lines
1.5 KiB
LLVM
; RUN: opt -domtree -instcombine -loops -S < %s | FileCheck %s
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; Note: The -loops above can be anything that requires the domtree, and is
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; necessary to work around a pass-manager bug.
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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; Function Attrs: nounwind uwtable
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define void @foo(i32* %a, i32* %b) #0 {
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entry:
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%ptrint = ptrtoint i32* %a to i64
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%maskedptr = and i64 %ptrint, 63
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%maskcond = icmp eq i64 %maskedptr, 0
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tail call void @llvm.assume(i1 %maskcond)
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%ptrint1 = ptrtoint i32* %b to i64
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%maskedptr2 = and i64 %ptrint1, 63
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%maskcond3 = icmp eq i64 %maskedptr2, 0
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tail call void @llvm.assume(i1 %maskcond3)
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br label %for.body
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; CHECK-LABEL: @foo
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; CHECK: load i32* {{.*}} align 64
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; CHECK: store i32 {{.*}} align 64
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; CHECK: ret
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for.body: ; preds = %entry, %for.body
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%indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
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%arrayidx = getelementptr inbounds i32* %b, i64 %indvars.iv
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%0 = load i32* %arrayidx, align 4
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%add = add nsw i32 %0, 1
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%arrayidx5 = getelementptr inbounds i32* %a, i64 %indvars.iv
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store i32 %add, i32* %arrayidx5, align 4
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%indvars.iv.next = add nuw nsw i64 %indvars.iv, 16
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%1 = trunc i64 %indvars.iv.next to i32
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%cmp = icmp slt i32 %1, 1648
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br i1 %cmp, label %for.body, label %for.end
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for.end: ; preds = %for.body
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ret void
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}
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; Function Attrs: nounwind
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declare void @llvm.assume(i1) #1
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attributes #0 = { nounwind uwtable }
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attributes #1 = { nounwind }
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