forked from OSchip/llvm-project
[AMDGPU] Add attribute for target loop unroll threshold default
Summary: Add a function attribute to allow the target specific default loop unroll threshold to be specified on a per-function basis. This allows a front-end to give guidance where it has insight that is not available to the back-end, while still allowing the target specific heuristics to also have an effect. Subscribers: arsenm, kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D68873
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@ -90,7 +90,8 @@ static bool dependsOnLocalPhi(const Loop *L, const Value *Cond,
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void AMDGPUTTIImpl::getUnrollingPreferences(Loop *L, ScalarEvolution &SE,
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TTI::UnrollingPreferences &UP) {
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UP.Threshold = 300; // Twice the default.
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const Function &F = *L->getHeader()->getParent();
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UP.Threshold = AMDGPU::getIntegerAttribute(F, "amdgpu-unroll-threshold", 300);
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UP.MaxCount = std::numeric_limits<unsigned>::max();
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UP.Partial = true;
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@ -0,0 +1,52 @@
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; RUN: opt < %s -S -mtriple=amdgcn-- -basicaa -loop-unroll | FileCheck %s
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; Check that the loop in unroll_default is not fully unrolled using the default
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; unroll threshold
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; CHECK-LABEL: @unroll_default
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; CHECK: entry:
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; CHECK: br i1 %cmp
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; CHECK: ret void
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; Check that the same loop in unroll_full is fully unrolled when the default
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; unroll threshold is increased by use of the amdgpu-unroll-threshold attribute
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; CHECK-LABEL: @unroll_full
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; CHECK: entry:
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; CHECK-NOT: br i1 %cmp
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; CHECK: ret void
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@in = internal unnamed_addr global i32* null, align 8
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@out = internal unnamed_addr global i32* null, align 8
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define void @unroll_default() {
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entry:
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br label %do.body
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do.body: ; preds = %entry
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%i.0 = phi i32 [ 0, %entry ], [ %inc, %do.body ]
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%v1 = load i64, i64* bitcast (i32** @in to i64*), align 8
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store i64 %v1, i64* bitcast (i32** @out to i64*), align 8
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%inc = add nsw i32 %i.0, 1
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%cmp = icmp slt i32 %inc, 100
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br i1 %cmp, label %do.body, label %do.end
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do.end: ; preds = %do.body
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ret void
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}
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define void @unroll_full() #0 {
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entry:
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br label %do.body
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do.body: ; preds = %entry
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%i.0 = phi i32 [ 0, %entry ], [ %inc, %do.body ]
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%v1 = load i64, i64* bitcast (i32** @in to i64*), align 8
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store i64 %v1, i64* bitcast (i32** @out to i64*), align 8
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%inc = add nsw i32 %i.0, 1
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%cmp = icmp slt i32 %inc, 100
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br i1 %cmp, label %do.body, label %do.end
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do.end: ; preds = %do.body
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ret void
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}
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attributes #0 = { "amdgpu-unroll-threshold"="1000" }
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