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AMDGPU: Fix runtime unrolling when cascaded GEPs present (#147700)

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Cascaded GEP (i.e. GEP of GEP) are not handled when determining if it is
ok to runtime unroll loops.

This change simply uses `getUnderlyingObjects` to look through cascaded
GEPs.
This commit is contained in:
macurtis-amd
2025-07-10 03:44:04 -05:00
committed by GitHub
parent 2e38beebcf
commit cff4a00d3f
2 changed files with 70 additions and 3 deletions
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9
llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
View File

@@ -216,10 +216,13 @@ void AMDGPUTTIImpl::getUnrollingPreferences(
// a variable, most likely we will be unable to combine it.
// Do not unroll too deep inner loops for local memory to give a chance
// to unroll an outer loop for a more important reason.
if (LocalGEPsSeen > 1 || L->getLoopDepth() > 2 ||
(!isa<GlobalVariable>(GEP->getPointerOperand()) &&
!isa<Argument>(GEP->getPointerOperand())))
if (LocalGEPsSeen > 1 || L->getLoopDepth() > 2)
continue;
const Value *V = getUnderlyingObject(GEP->getPointerOperand());
if (!isa<GlobalVariable>(V) && !isa<Argument>(V))
continue;
LLVM_DEBUG(dbgs() << "Allow unroll runtime for loop:\n"
<< *L << " due to LDS use.\n");
UP.Runtime = UnrollRuntimeLocal;

64
llvm/test/Transforms/LoopUnroll/AMDGPU/unroll-runtime.ll Normal file
View File

@@ -0,0 +1,64 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -mtriple=amdgcn-amd-amdhsa -passes=loop-unroll -S %s -o - | FileCheck %s
%struct.wombat = type { %struct.zot, i32, [16 x i32], [16 x i32], i32, i32, [16 x i32], i32 }
%struct.zot = type { i32, i32, [1024 x i32] }
@global = external addrspace(3) global %struct.wombat
; Ensure that a cascaded GEP for local address space does not inhibit unrolling
;
define amdgpu_kernel void @unroll_when_cascaded_gep(i32 %arg) {
; CHECK-LABEL: @unroll_when_cascaded_gep(
; CHECK-NEXT: bb:
; CHECK-NEXT: [[TMP0:%.*]] = add i32 [[ARG:%.*]], 1
; CHECK-NEXT: [[XTRAITER:%.*]] = and i32 [[TMP0]], 7
; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i32 [[ARG]], 7
; CHECK-NEXT: br i1 [[TMP1]], label [[BB2_UNR_LCSSA:%.*]], label [[BB_NEW:%.*]]
; CHECK: bb.new:
; CHECK-NEXT: [[UNROLL_ITER:%.*]] = sub i32 [[TMP0]], [[XTRAITER]]
; CHECK-NEXT: br label [[BB1:%.*]]
; CHECK: bb1:
; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ 0, [[BB_NEW]] ], [ [[ADD_7:%.*]], [[BB1]] ]
; CHECK-NEXT: [[NITER:%.*]] = phi i32 [ 0, [[BB_NEW]] ], [ [[NITER_NEXT_7:%.*]], [[BB1]] ]
; CHECK-NEXT: [[ADD_7]] = add i32 [[PHI]], 8
; CHECK-NEXT: [[NITER_NEXT_7]] = add i32 [[NITER]], 8
; CHECK-NEXT: [[NITER_NCMP_7:%.*]] = icmp eq i32 [[NITER_NEXT_7]], [[UNROLL_ITER]]
; CHECK-NEXT: br i1 [[NITER_NCMP_7]], label [[BB2_UNR_LCSSA_LOOPEXIT:%.*]], label [[BB1]]
; CHECK: bb2.unr-lcssa.loopexit:
; CHECK-NEXT: [[PHI_UNR_PH:%.*]] = phi i32 [ [[ADD_7]], [[BB1]] ]
; CHECK-NEXT: br label [[BB2_UNR_LCSSA]]
; CHECK: bb2.unr-lcssa:
; CHECK-NEXT: [[PHI_UNR:%.*]] = phi i32 [ 0, [[BB:%.*]] ], [ [[PHI_UNR_PH]], [[BB2_UNR_LCSSA_LOOPEXIT]] ]
; CHECK-NEXT: [[LCMP_MOD:%.*]] = icmp ne i32 [[XTRAITER]], 0
; CHECK-NEXT: br i1 [[LCMP_MOD]], label [[BB1_EPIL_PREHEADER:%.*]], label [[BB2:%.*]]
; CHECK: bb1.epil.preheader:
; CHECK-NEXT: br label [[BB1_EPIL:%.*]]
; CHECK: bb1.epil:
; CHECK-NEXT: [[PHI_EPIL:%.*]] = phi i32 [ [[PHI_UNR]], [[BB1_EPIL_PREHEADER]] ], [ [[ADD_EPIL:%.*]], [[BB1_EPIL]] ]
; CHECK-NEXT: [[EPIL_ITER:%.*]] = phi i32 [ 0, [[BB1_EPIL_PREHEADER]] ], [ [[EPIL_ITER_NEXT:%.*]], [[BB1_EPIL]] ]
; CHECK-NEXT: [[GETELEMENTPTR_EPIL:%.*]] = getelementptr [1024 x i32], ptr addrspace(3) getelementptr inbounds nuw (i8, ptr addrspace(3) @global, i32 8), i32 0, i32 0
; CHECK-NEXT: [[ADD_EPIL]] = add i32 [[PHI_EPIL]], 1
; CHECK-NEXT: [[ICMP_EPIL:%.*]] = icmp eq i32 [[PHI_EPIL]], [[ARG]]
; CHECK-NEXT: [[EPIL_ITER_NEXT]] = add i32 [[EPIL_ITER]], 1
; CHECK-NEXT: [[EPIL_ITER_CMP:%.*]] = icmp ne i32 [[EPIL_ITER_NEXT]], [[XTRAITER]]
; CHECK-NEXT: br i1 [[EPIL_ITER_CMP]], label [[BB1_EPIL]], label [[BB2_EPILOG_LCSSA:%.*]], !llvm.loop [[LOOP0:![0-9]+]]
; CHECK: bb2.epilog-lcssa:
; CHECK-NEXT: br label [[BB2]]
; CHECK: bb2:
; CHECK-NEXT: ret void
;
bb:
br label %bb1
bb1: ; preds = %bb1, %bb
%phi = phi i32 [ 0, %bb ], [ %add, %bb1 ]
%getelementptr = getelementptr [1024 x i32], ptr addrspace(3) getelementptr inbounds nuw (i8, ptr addrspace(3) @global, i32 8), i32 0, i32 0
%add = add i32 %phi, 1
%icmp = icmp eq i32 %phi, %arg
br i1 %icmp, label %bb2, label %bb1
bb2: ; preds = %bb1
ret void
}