[llvm] 3c1273d - [AMDGPU] Add amdgpu specific loop threshold metadata
Tim Corringham via llvm-commits
llvm-commits at lists.llvm.org
Thu Oct 22 09:22:58 PDT 2020
Author: Tim Corringham
Date: 2020-10-22T17:21:32+01:00
New Revision: 3c1273d7378e1d51abf9b43c764ccb9828e4a26a
URL: https://github.com/llvm/llvm-project/commit/3c1273d7378e1d51abf9b43c764ccb9828e4a26a
DIFF: https://github.com/llvm/llvm-project/commit/3c1273d7378e1d51abf9b43c764ccb9828e4a26a.diff
LOG: [AMDGPU] Add amdgpu specific loop threshold metadata
Add new loop metadata amdgpu.loop.unroll.threshold to allow the initial AMDGPU
specific unroll threshold value to be specified on a loop by loop basis.
The intention is to be able to to allow more nuanced hints, e.g. specifying a
low threshold value to indicate that a loop may be unrolled if cheap enough
rather than using the all or nothing llvm.loop.unroll.disable metadata.
Differential Revision: https://reviews.llvm.org/D84779
Added:
llvm/test/Transforms/LoopUnroll/AMDGPU/unroll-threshold.ll
Modified:
llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
index 78dc20b0b671..31585ed5b9e4 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
@@ -117,6 +117,26 @@ void AMDGPUTTIImpl::getUnrollingPreferences(Loop *L, ScalarEvolution &SE,
const unsigned MaxAlloca = (256 - 16) * 4;
unsigned ThresholdPrivate = UnrollThresholdPrivate;
unsigned ThresholdLocal = UnrollThresholdLocal;
+
+ // If this loop has the amdgpu.loop.unroll.threshold metadata we will use the
+ // provided threshold value as the default for Threshold
+ if (MDNode *LoopUnrollThreshold =
+ findOptionMDForLoop(L, "amdgpu.loop.unroll.threshold")) {
+ if (LoopUnrollThreshold->getNumOperands() == 2) {
+ ConstantInt *MetaThresholdValue = mdconst::extract_or_null<ConstantInt>(
+ LoopUnrollThreshold->getOperand(1));
+ if (MetaThresholdValue) {
+ // We will also use the supplied value for PartialThreshold for now.
+ // We may introduce additional metadata if it becomes necessary in the
+ // future.
+ UP.Threshold = MetaThresholdValue->getSExtValue();
+ UP.PartialThreshold = UP.Threshold;
+ ThresholdPrivate = std::min(ThresholdPrivate, UP.Threshold);
+ ThresholdLocal = std::min(ThresholdLocal, UP.Threshold);
+ }
+ }
+ }
+
unsigned MaxBoost = std::max(ThresholdPrivate, ThresholdLocal);
for (const BasicBlock *BB : L->getBlocks()) {
const DataLayout &DL = BB->getModule()->getDataLayout();
diff --git a/llvm/test/Transforms/LoopUnroll/AMDGPU/unroll-threshold.ll b/llvm/test/Transforms/LoopUnroll/AMDGPU/unroll-threshold.ll
new file mode 100644
index 000000000000..5c551afdc4bf
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/AMDGPU/unroll-threshold.ll
@@ -0,0 +1,113 @@
+; RUN: opt < %s -S -mtriple=amdgcn-- -loop-unroll | FileCheck %s
+
+; Check the handling of amdgpu.loop.unroll.threshold metadata which can be used to
+; set the default threshold for a loop. This metadata overrides both the AMDGPU
+; default, and any value specified by the amdgpu-unroll-threshold function attribute
+; (which sets a threshold for all loops in the function).
+
+; Check that the loop in unroll_default is not fully unrolled using the default
+; unroll threshold
+; CHECK-LABEL: @unroll_default
+; CHECK: entry:
+; CHECK: br i1 %cmp
+; CHECK: ret void
+
+ at in = internal unnamed_addr global i32* null, align 8
+ at out = internal unnamed_addr global i32* null, align 8
+
+define void @unroll_default() {
+entry:
+ br label %do.body
+
+do.body: ; preds = %entry
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %do.body ]
+ %v1 = load i64, i64* bitcast (i32** @in to i64*), align 8
+ store i64 %v1, i64* bitcast (i32** @out to i64*), align 8
+ %inc = add nsw i32 %i.0, 1
+ %cmp = icmp slt i32 %inc, 100
+ br i1 %cmp, label %do.body, label %do.end
+
+do.end: ; preds = %do.body
+ ret void
+}
+
+; Check that the same loop in unroll_full is fully unrolled when the default
+; unroll threshold is increased by use of the amdgpu.loop.unroll.threshold metadata
+; CHECK-LABEL: @unroll_full
+; CHECK: entry:
+; CHECK-NOT: br i1 %cmp
+; CHECK: ret void
+
+define void @unroll_full() {
+entry:
+ br label %do.body
+
+do.body: ; preds = %entry
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %do.body ]
+ %v1 = load i64, i64* bitcast (i32** @in to i64*), align 8
+ store i64 %v1, i64* bitcast (i32** @out to i64*), align 8
+ %inc = add nsw i32 %i.0, 1
+ %cmp = icmp slt i32 %inc, 100
+ br i1 %cmp, label %do.body, label %do.end, !llvm.loop !1
+
+do.end: ; preds = %do.body
+ ret void
+}
+
+; Check that the same loop in override_no_unroll is not unrolled when a high default
+; unroll threshold specified using the amdgpu-unroll-threshold function attribute
+; is overridden by a low threshold using the amdgpu.loop.unroll.threshold metadata
+
+; CHECK-LABEL: @override_no_unroll
+; CHECK: entry:
+; CHECK: br i1 %cmp
+; CHECK: ret void
+
+define void @override_no_unroll() #0 {
+entry:
+ br label %do.body
+
+do.body: ; preds = %entry
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %do.body ]
+ %v1 = load i64, i64* bitcast (i32** @in to i64*), align 8
+ store i64 %v1, i64* bitcast (i32** @out to i64*), align 8
+ %inc = add nsw i32 %i.0, 1
+ %cmp = icmp slt i32 %inc, 100
+ br i1 %cmp, label %do.body, label %do.end, !llvm.loop !3
+
+do.end: ; preds = %do.body
+ ret void
+}
+
+; Check that the same loop in override_unroll is fully unrolled when a low default
+; unroll threshold specified using the amdgpu-unroll-threshold function attribute
+; is overridden by a high threshold using the amdgpu.loop.unroll.threshold metadata
+
+; CHECK-LABEL: @override_unroll
+; CHECK: entry:
+; CHECK-NOT: br i1 %cmp
+; CHECK: ret void
+
+define void @override_unroll() #1 {
+entry:
+ br label %do.body
+
+do.body: ; preds = %entry
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %do.body ]
+ %v1 = load i64, i64* bitcast (i32** @in to i64*), align 8
+ store i64 %v1, i64* bitcast (i32** @out to i64*), align 8
+ %inc = add nsw i32 %i.0, 1
+ %cmp = icmp slt i32 %inc, 100
+ br i1 %cmp, label %do.body, label %do.end, !llvm.loop !1
+
+do.end: ; preds = %do.body
+ ret void
+}
+
+attributes #0 = { "amdgpu-unroll-threshold"="1000" }
+attributes #1 = { "amdgpu-unroll-threshold"="100" }
+
+!1 = !{!1, !2}
+!2 = !{!"amdgpu.loop.unroll.threshold", i32 1000}
+!3 = !{!3, !4}
+!4 = !{!"amdgpu.loop.unroll.threshold", i32 100}
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